Dodge Code P1389: Explanations, Causes and Solutions

The P1389 code is a specific code for Dodge vehicles (Stellantis group), related to the ASD (Auto Shutdown Relay) relay circuit. This relay is essential for supplying electricity to critical engine components, such as the injectors, ignition coil, or crankshaft sensor. Here is a complete guide to understanding and resolving this issue.

Meaning of Code P1389

The ASD relay acts as a safety switch controlled by the Powertrain Control Module (PCM). It cuts off the engine’s electrical power if anomalies are detected (e.g., absence of signal from the crankshaft sensor). Code P1389 is triggered when the PCM detects a malfunction in the ASD relay circuit, such as irregular voltage or a missing signal.

Possible Causes

  1. Faulty ASD Relay:
    • Oxidized, stuck, or worn internal contacts.
  2. Electrical Issues:
    • Blown fuse (often in the under-hood fuse box).
    • Cut wires, short to ground, or corroded connectors.
  3. Crankshaft Sensor Failure (related to the ASD circuit):
    • An incorrect signal from the sensor can disrupt the relay’s operation.
  4. PCM Failure (rare).

Common Symptoms

  • 🚨 Engine light on (Check Engine message).
  • 🔌 Engine stalling abruptly or not starting.
  • ⚡ No spark or fuel injection (diagnosed via OBD2 scanner).

Diagnosis and Repairs

Verification Steps

  1. Check the ASD Fuse:
    • Locate the fuse associated with the ASD relay (consult the Dodge manual). Replace it if blown.
  2. Test the ASD Relay:
    • Swap it with an identical relay (e.g., headlight relay) to check its operation.
    • Use a multimeter to test continuity and resistance (expected values: ~50-120 ohms).
  3. Inspect the Crankshaft Sensor:
    • Check its connector and wiring. Test its resistance (typically 200-1000 ohms depending on the model).
  4. Check the Electrical Circuit:
    • Look for exposed wires, melted insulation, or oxidized connectors between the PCM, ASD relay, and battery.

Common Solutions

  1. Replace the ASD Relay:
    • Cost: €15 to €50. Choose a compatible part (e.g., Mopar or equivalent).
  2. Repair the Wiring:
    • Use heat shrink tubing to insulate damaged wires.
  3. Replace the Crankshaft Sensor (if necessary).

Code Reset

  • Use an OBD2 scanner to clear the P1389 code after repair. Perform a driving test to confirm resolution.

Affected Dodge Models

This code is common on Dodge vehicles equipped with 2.4L, 3.3L, 3.8L, or 5.7L HEMI engines, including:

  • Dodge Grand Caravan
  • Dodge Durango
  • Dodge Ram 1500
  • Dodge Charger/Challenger (certain years).

Safety Tips

  • 🔋 Disconnect the battery before any electrical work to avoid short circuits.
  • 🔧 Consult a repair manual specific to your Dodge model to accurately locate the ASD relay and crankshaft sensor.

When to Consult a Professional?

If the code persists after replacing the ASD relay and checking the circuit, a garage can:

  • Diagnose a possible PCM failure.
  • Analyze the crankshaft sensor signal in depth with an oscilloscope.

In summary: The P1389 code on Dodge indicates a problem with the ASD relay circuit, often resolved by replacing the relay or repairing the wiring. Prompt action prevents unpredictable engine failures. 🔧⚡

Ford Code P1389: Explanations, Causes and Solutions

Code P1389 is a specific code for Ford vehicles, related to a malfunction of the ignition coil primary circuit (usually associated with cylinder No. 1). This code indicates an electrical problem in the coil control circuit, essential for generating the spark needed for combustion. Here is a comprehensive guide to diagnosing and fixing this fault.

Meaning of Code P1389

The ignition coil converts the battery’s low voltage into high voltage to create the spark in the spark plugs. The Powertrain Control Module (PCM) monitors the coil’s primary circuit. Code P1389 is triggered when the PCM detects:

  • An abnormal resistance (open circuit or short circuit).
  • An irregular voltage in the ignition coil primary circuit (cylinder 1).

Possible Causes

  1. Faulty ignition coil (cylinder 1):
    • Damaged internal windings, overheating, or moisture.
  2. Electrical issues:
    • Cut wires, oxidized connectors, or short circuit to ground.
    • Blown fuse related to the ignition circuit.
  3. PCM failure (rare):
    • Signal error or hardware failure.

Common Symptoms

  • 🚨 Engine light on (Check Engine).
  • 💥 Engine shaking or misfires (especially at idle).
  • 🐌 Loss of power or hesitant acceleration.
  • ⛽ Increased fuel consumption.

Diagnosis and Repairs

Inspection Steps

  1. Inspect the ignition coil (cylinder 1):
    • Look for cracks, burn marks, or corrosion.
    • Compare its primary resistance with Ford specifications (typically 0.5 to 2 ohms) using a multimeter.
  2. Check the electrical circuit:
    • Check the fuse associated with ignition (refer to the Ford manual).
    • Test the supply voltage (12V) and the coil ground.
    • Inspect connectors and wires for signs of oxidation or damage.
  3. Test the PCM signal:
    • Use an oscilloscope to check the control signal sent by the PCM to the coil.

Common Solutions

  1. Replace the ignition coil:
    • Choose a compatible part (e.g., Motorcraft for Ford). Cost: 50 to 150 €.
  2. Repair the wiring:
    • Repair damaged wires with heat shrink tubing. Clean oxidized connectors.
  3. Replace the blown fuse:
    • Use a fuse with the same amperage (e.g., 15A or 20A depending on the model).

Affected Ford Models

This code is common on Ford vehicles with 4-cylinder (EcoBoost), V6, or V8 engines, including:

  • Ford F-150
  • Ford Focus
  • Ford Escape
  • Ford Explorer

Safety Tips

  • 🔋 Disconnect the battery before handling electrical components.
  • 🔧 Use insulated tools to avoid short circuits.

Resetting the Code

  • Use an OBD2 scanner to clear the P1389 code after repair. Perform a driving test to confirm the fault does not reappear.

When to Consult a Professional?

  • If the code persists after replacing the coil and checking the circuit.
  • To diagnose a possible PCM failure or related CKP (crankshaft) sensor issue.

In summary: Code P1389 on Ford points to a problem with the ignition coil primary circuit (cylinder 1). Prompt action prevents misfires and preserves engine performance.

Jeep Code P1389: Explanations, Causes and Solutions

The P1389 code on Jeep vehicles (Stellantis group) is related to the ASD (Auto Shutdown Relay) relay circuit, a key component that supplies electricity to essential engine elements such as the injectors, ignition coil, or crankshaft sensor. Here is a complete guide to diagnose and resolve this issue.

Meaning of the P1389 Code

The ASD relay acts as a safety switch controlled by the Powertrain Control Module (PCM). It cuts off electrical power in case of a critical anomaly (e.g., absence of signal from the crankshaft sensor). The P1389 code is stored when the PCM detects a malfunction in the ASD relay circuit, such as irregular voltage or a missing signal.

Possible Causes

  1. Faulty ASD Relay:
    • Oxidized, stuck, or worn internal contacts.
  2. Electrical Issues:
    • Blown fuse (often in the under-hood fuse box).
    • Cut wires, short circuit to ground, or corroded connectors.
  3. Crankshaft Sensor Failure:
    • An erroneous signal disrupts the ASD relay operation.
  4. PCM Failure (rare).

Common Symptoms

  • 🚨 Engine light on (Check Engine).
  • 🔌 Engine stalling abruptly or not starting.
  • ⚡ No spark or fuel injection (diagnosed via OBD2 scanner).

Diagnosis and Repairs

Verification Steps

  1. Check the ASD Fuse:
    • Locate the fuse associated with the ASD relay (refer to the Jeep manual). Replace it if blown.
  2. Test the ASD Relay:
    • Swap it with an identical relay (e.g., headlight relay) to check its operation.
    • Test continuity and resistance with a multimeter (expected: ~50-120 ohms).
  3. Inspect the Crankshaft Sensor:
    • Check its connector and wiring. Test its resistance (generally 200-1000 ohms depending on the model).
  4. Check the Electrical Circuit:
    • Look for exposed wires, melted insulation, or oxidized connectors between the PCM, ASD relay, and battery.

Common Solutions

  1. Replace the ASD Relay:
    • Cost: €15 to €50. Opt for a compatible part (e.g., Mopar for Jeep).
  2. Repair the Wiring:
    • Insulate damaged wires with heat shrink tubing.
  3. Replace the Crankshaft Sensor (if necessary).

Affected Jeep Models

This code is common on Jeeps equipped with 3.7L, 4.0L, or 4.7L engines, including:

  • Jeep Grand Cherokee (WJ/WK)
  • Jeep Wrangler (TJ/JK)
  • Jeep Liberty (KJ/KK).

Safety Tips

  • 🔋 Disconnect the battery before any electrical work.
  • 🔧 Consult a repair manual specific to your Jeep model to locate the ASD relay (often in the PDC box under the hood).

Resetting the Code

  • Use an OBD2 scanner to clear the P1389 code after repair. Perform a test drive to confirm resolution.

When to Consult a Professional?

If the code persists after replacing the ASD relay and checking the circuit, a garage can:

  • Diagnose a possible PCM failure.
  • Analyze the crankshaft sensor signal with an oscilloscope.

In summary: The P1389 code on Jeep indicates a problem with the ASD relay circuit. Prompt action prevents unpredictable engine failures and ensures vehicle reliability.

Volkswagen Code P1389: Explanations, Causes and Solutions

The P1389 code on Volkswagen vehicles is a manufacturer-specific code, typically related to a malfunction in the fuel pump relay control circuit or an anomaly in the engine management system. This code can affect fuel supply or the engine’s electrical communication. Here is a detailed guide to diagnose and resolve this issue.

Meaning of Code P1389

The P1389 code indicates that the Engine Control Module (ECM) has detected an anomaly in the fuel pump relay circuit or another critical system controlled by the ECM. Depending on the VW model, this code may also be associated with:

  • A fault in the injector circuit (e.g., electrical resistance outside specifications).
  • A communication error with the injection system.
  • A voltage issue in the ECM power supply circuit.

Possible Causes

  1. Faulty Fuel Pump Relay:
    • Oxidized contacts, relay stuck in open/closed position.
  2. Electrical Issues:
    • Blown fuse (often in the fuse box under the hood or inside the cabin).
    • Damaged wires, corroded connectors, or short circuit to ground.
  3. Fuel Pump Failure:
    • Internal wear, seized pump motor, or abnormal resistance.
  4. ECM Malfunction (rare):
    • Software or hardware issue in the control module.

Common Symptoms

  • 🚨 Engine light on (Check Engine).
  • 🔌 Engine hard to start or sudden stalling.
  • ⛽ Silent fuel pump at startup (no humming).
  • 🐌 Loss of power or jerking during acceleration.

Diagnosis and Repairs

Verification Steps

  1. Check the Fuel Pump Fuse:
    • Consult the Volkswagen manual to locate the fuse (e.g., 15A or 20A). Replace if blown.
  2. Test the Fuel Pump Relay:
    • Locate the relay (often in the electrical box near the steering wheel).
    • Swap it with an identical relay (e.g., headlight relay) to check its function.
  3. Check the Fuel Pump:
    • Disconnect the pump connector and measure its resistance with a multimeter (expected: 1 to 5 ohms).
    • Listen for a hum at startup (if the pump is silent, it is likely faulty).
  4. Inspect the Electrical Circuit:
    • Look for exposed wires, melted insulation, or corroded connectors between the ECM, relay, and pump.

Common Solutions

  1. Replace the Fuel Pump Relay:
    • Cost: €20 to €60. Choose a compatible part (e.g., Bosch or VW OEM).
  2. Repair the Wiring:
    • Insulate damaged wires with heat-shrink tubing. Clean connectors with contact spray.
  3. Replace the Fuel Pump:
    • If faulty, opt for a new or remanufactured pump.

Affected Volkswagen Models

This code is common in the following models (depending on the engine):

  • Volkswagen Golf (Mk5 to Mk7)
  • Volkswagen Passat (B6 to B8)
  • Volkswagen Tiguan
  • Volkswagen Jetta

Safety Tips

  • 🔋 Disconnect the battery before any electrical work.
  • ⚠️ Avoid sparks near the fuel tank during repairs.

Resetting the Code

  • Use a VW-compatible OBD2 scanner (e.g., VCDS) to clear the P1389 code after repair.

When to Consult a Professional?

  • If the code persists despite replacing the relay and pump.
  • To diagnose a potential ECM failure or related sensors (e.g., fuel pressure sensor).

In summary: The P1389 code on Volkswagen often points to an issue with the fuel pump circuit or its relay. Prompt action prevents unexpected breakdowns and restores engine performance.

Ford Code P138A: Explanations, Causes and Solutions

The P138A code is an OBD-II code specific to Ford, typically associated with a malfunction in the ignition coil primary circuit (often related to cylinder #1). This code indicates that the Powertrain Control Module (PCM) has detected an electrical anomaly in the ignition coil control circuit, which can disrupt the generation of the spark needed for combustion. Here is a comprehensive guide for diagnosing and resolving this issue.

Meaning of Code P138A

The ignition coil converts the battery’s low voltage into high voltage to power the spark plugs. The PCM monitors the resistance and voltage of the coil’s primary circuit. Code P138A is triggered when:

  • The primary circuit resistance is outside specifications (open circuit or short circuit).
  • The PCM detects abnormal voltage or an irregular signal.

Possible Causes

  1. Faulty Ignition Coil (cylinder 1):
    • Damaged internal windings, cracks, moisture, or overheating.
  2. Electrical Issues:
    • Cut wires, oxidized connectors, or short circuit to ground.
    • Blown fuse in the ignition circuit.
  3. PCM Failure (rare):
    • Communication error or hardware failure.

Common Symptoms

  • 🚨 Check Engine Light On.
  • 💥 Engine Misfires (engine shaking, especially at idle).
  • 🐌 Loss of Power or hesitant acceleration.
  • ⛽ Increased Fuel Consumption.

Diagnosis and Repairs

Inspection Steps

  1. Inspect the Ignition Coil (cylinder 1):
    • Remove the coil and check for cracks, burn marks, or corrosion.
    • Measure the primary resistance with a multimeter:
      • Normal Value: 0.5 to 2 ohms (depending on Ford model).
      • If resistance is infinite (open circuit) or too low (< 0.5 Ω) → Faulty coil.
  2. Check the Electrical Circuit:
    • Check the fuse associated with the ignition circuit (refer to Ford manual).
    • Test the supply voltage (12V) and ground at the coil connector.
    • Look for exposed wires or oxidized connectors.
  3. Test the PCM Signal:
    • Use an oscilloscope to check the control signal sent by the PCM to the coil.

Common Solutions

  1. Replace the Ignition Coil:
    • Choose a compatible part (e.g., Motorcraft for Ford). Cost: €50 to €150.
  2. Repair the Wiring:
    • Repair damaged wires with heat shrink tubing. Clean connectors with contact spray.
  3. Replace the Blown Fuse:
    • Use a fuse with the same amperage (e.g., 15A or 20A).

Affected Ford Models

This code is common on Ford vehicles equipped with EcoBoost, Duratec, or V8 engines, including:

  • Ford F-150
  • Ford Focus
  • Ford Escape
  • Ford Mustang

Safety Tips

  • 🔋 Disconnect the battery before any electrical work.
  • 🔧 Use insulated gloves to avoid electric shocks.

Code Reset

  • Use an OBD2 scanner to clear the P138A code after repair. Perform a drive test to ensure the fault does not reappear.

When to Consult a Professional?

  • If the code persists after replacing the coil and checking the circuit.
  • To diagnose a possible PCM failure or a crankshaft position sensor (CKP) issue.

In summary: The P138A code on Ford indicates a problem with the ignition coil primary circuit (cylinder 1). Prompt action prevents misfires and preserves engine performance.

Understanding and Resolving Ford Fault Code P138A

The default code P138A is an OBD-II code specific to Ford, Lincoln, and Mercury vehicles. It indicates a problem related to the Variable Camshaft Timing (VCT) system or its control circuit, specifically concerning the VCT system’s oil pressure sensor. This fault can lead to a loss of performance, increased fuel consumption, and illumination of the check engine light (⚠️).

1. Meaning of Code P138A

  • Official Definition:
    * “P138A – VCT System Oil Pressure Sensor – Circuit ‘B’ Range/Performance.” *
    This code signals an anomaly in the electrical circuit or operating range of the oil pressure sensor associated with the VCT system (typically on the “B” side of the engine, often corresponding to cylinders 2, 3, and 6).
  • Role of the VCT System:
    The VCT system adjusts the camshaft’s advance or retard in real-time to optimize:
    • Power and torque.
    • Energy efficiency.
    • Reduction of polluting emissions.

2. Common Symptoms

  • 🚨 Check engine light illuminated (MIL).
  • ⚠️ Noticeable loss of power during acceleration.
  • 🔥 Rough idle (engine shaking at idle).
  • ⛽ Increased fuel consumption (up to 15-20%).
  • 🐌 Delayed throttle response.
  • ⚠️ Engine stalling or operation in degraded mode (“Limp Mode”).

3. Possible Causes

Here are the most frequent causes listed in order of probability:

Order Cause Description
1 Oil level/pressure issue Low level, aging oil, clogged oil filter, weak oil pump.
2 Faulty oil pressure sensor Internal failure, damaged electrical circuit (wires, connectors).
3 VCT solenoid problem Solenoid stuck (open/closed) or clogged by deposits.
4 Unsuitable engine oil Incorrect viscosity (e.g., 5W-20 required but 10W-40 used).
5 Wiring/connector issue Broken wires, oxidation, short circuits.
6 PCM module failure Rare, but possible (faulty electronic management).

4. Step-by-Step Diagnosis

Required Tools:

  • OBD-II scanner (with advanced functions for Ford).
  • Digital multimeter.
  • Oil pressure gauge.

Steps:

  1. Check the oil level and condition:
    • Check the level with the dipstick.
    • If the oil is black or viscous, perform an oil change.
  2. Test the oil pressure:
    • Use a pressure gauge (expected value: 20-80 PSI depending on RPM).
    • Low pressure = pump/filter problem.
  3. Inspect the sensor and its circuit:
    • Disconnect the sensor connector.
    • Test the supply voltage (typically 5V or 12V).
    • Check for continuity and absence of short circuits.
  4. Check the VCT solenoid:
    • Measure the resistance (typical value: 5–15 Ω).
    • Clean the solenoid with a specific degreaser.
  5. Analyze live data:
    • With a scanner, compare the oil pressure sensor values with manufacturer specifications.
    • Observe the status of the VCT solenoids (% activation).

5. Repair Solutions

  • If oil degraded/low level:
    ➡️ Complete oil change + new filter + oil compliant with the manual (e.g., 5W-20).
  • Faulty sensor:
    ➡️ Replace the sensor (average cost: 80–150 €).
    Affected models: Focus, Fiesta, Escape, Explorer (2010–2020).
  • Stuck VCT solenoid:
    ➡️ Clean or replace (cost: 100–250 €).
  • Damaged wiring:
    ➡️ Repair wires or replace the connector.
  • Persistent low oil pressure:
    ➡️ Check the oil pump or clogged filter.

6. Average Repair Costs

Item Part Price Labor Total
Oil pressure sensor 80–150 € 50–100 € 130–250 €
VCT solenoid 90–200 € 100–150 € 190–350 €
Complete oil change 40–70 € 30–50 € 70–120 €

7. Prevention

  • ✅ Regular oil changes (follow the maintenance schedule).
  • ✅ Use the recommended engine oil by Ford.
  • ✅ Check the oil level monthly.
  • ✅ Avoid repeated short trips (promotes clogging).

Conclusion

The P138A code on Ford vehicles is often related to a mechanical or electrical problem in the VCT system, generally easy to resolve if diagnosed early. Clean and suitable oil is the first lead to check. Ignoring this fault can damage the VCT system, leading to costly repairs (e.g., camshaft replacement). If in doubt, consult a Ford specialist mechanic equipped with appropriate diagnostic tools.

Decoding the Ford P138B Fault Code

1. Meaning of Code P138B

  • Official Definition:
    *”P138B – VCT System Oil Pressure Sensor – Circuit ‘A’ Range/Performance.”*
    This code indicates an electrical or hydraulic anomaly in the oil pressure sensor circuit related to the VCT system, specifically on the “A” side of the engine (typically cylinders 1, 4, and 5 on V6/V8 engines).
  • Key Role:
    The VCT system (“Variable Camshaft Timing“) adjusts camshaft timing in real-time to optimize:
    ▶️ Combustion,
    ▶️ Performance,
    ▶️ Fuel consumption.

2. Common Symptoms

  • ✅ Check Engine Light (MIL) illuminated.
  • ⚠️ Abnormal vibrations at idle (rough idle).
  • 🔻 Noticeable power loss during acceleration.
  • ⛽ Increased fuel consumption (+15-25%).
  • ⚠️ Hard starting in cold weather.
  • 🚫 Limp mode activation (limited power).

3. Probable Causes (by frequency)

# Cause Technical Details
1 Inadequate engine oil Incorrect viscosity (e.g., 5W-20 required but 10W-40 used), oxidized oil.
2 Hydraulic issue Low level, clogged oil filter, worn oil pump.
3 Faulty pressure sensor Internal failure, sensor clogged with deposits.
4 VCT solenoid failure Circuit “A” stuck/open, burnt coil (resistance out of specification).
5 Wiring problem Damaged wires, oxidized connectors, short circuit/poor ground.
6 Faulty PCM Rare (diagnosed after eliminating other causes).

4. Step-by-Step Diagnosis

Required tools: Advanced OBD-II scanner (e.g., FORScan), multimeter, oil pressure gauge.

Step Action
1 Check the oil : Level, viscosity, color. Change if necessary.
2 Test oil pressure (at idle/3,000 RPM): Normal value: 20-80 PSI.
3 Scan live data :
– Compare oil pressure on side “A” with manufacturer specifications.
– Observe VCT solenoid “A” status (% activation).
4 Inspect sensor/wiring :
– Measure supply voltage (5V/12V).
– Test continuity and resistance (typical value: 800-1200 Ω).
5 Check VCT solenoid “A” :
– Expected resistance: 5-15 Ω.
– Clean using specific degreaser.

5. Repair Solutions

  • Incorrect oil/low level :
    → Oil change + new filter + 5W-20/5W-30 synthetic oil (as per manual).
  • Faulty sensor :
    → Replace sensor on side “A” (cost: €70-160).
  • Faulty VCT solenoid :
    → Clean or replace (€120-220 part + labor).
  • Damaged wiring :
    → Repair wires/connectors (variable cost).
  • Low oil pressure :
    → Check oil pump/filter (total cost: €300-600).

Affected Ford models: F-150 (2015+), Explorer (2011-2020), Mustang (EcoBoost), Edge, Transit.

6. Average Repair Costs

Intervention Parts Labor Total
Sensor replacement €70-160 €50-90 €120-250
VCT solenoid replacement €100-200 €80-150 €180-350
Complete oil change €40-70 €30-60 €70-130

7. Prevention Tips

  • 🔧 Regular oil changes every 10,000-15,000 km (follow maintenance schedule).
  • ⚠️ Use only recommended oil by Ford (avoid mixtures).
  • 🔍 Monthly oil level check (cold engine, flat surface).
  • 🧼 Clean VCT system every 60,000 km to prevent clogging.

Conclusion

Code P138B indicates a malfunction in the “A” circuit of the VCT system, often resolved by an oil change or replacing the pressure sensor/solenoid. Prompt action is crucial to prevent:

  • Camshaft degradation,
  • Chronic overconsumption,
  • Turbocharger damage (on EcoBoost engines).

⚠️ Important : This code can be triggered by a simple drop in oil pressure. Consult a Ford specialist equipped with appropriate diagnostic tools (IDS/FDRS) for accurate troubleshooting.

Code P138C: Glow Plug Circuit/Performance Problem (Cylinder 3)

Common Signs

  • 🚩 Hard starting (especially in cold/damp weather),
  • ⚠️ Engine shaking or stalling at idle,
  • ⚡ Combustion issues (misfires),
  • 💡 Engine fault light (ESP/Check Engine) illuminated,
  • 📉 Increased fuel consumption.

Probable Causes

  1. Faulty glow plug (cylinder 3): Internal failure or resistance out of specification.
  2. Electrical issue:
    • Damaged/oxidized/short-circuited wires (between the module and glow plug #3),
    • Loose or corroded connectors.
  3. Control module failure (GPCM): Malfunction in the circuit managing cylinder 3.
  4. Failed glow plug relay: Unable to power the circuit.
  5. Blown fuse: In the glow plug power circuit.

Recommended Diagnosis

  1. Check glow plug #3 resistance (typical value: 0.1–2 Ω). Infinite resistance = faulty plug.
  2. Visually inspect wiring: Look for burns, cuts, or corrosion on cylinder 3’s circuit.
  3. Test power supply: Use a multimeter to check voltage at the glow plug terminals during startup.
  4. Check relay and fuses: Ensure they are functioning properly.
  5. Scan the GPCM module: Look for other related fault codes (e.g., P138A, P138B, P138D).

⚠️ Important: A faulty glow plug can damage the control module. Always test both!

Repair

  • Replace glow plug #3 (average cost: €20–80 per unit),
  • Repair damaged wires/connectors,
  • Replace GPCM module or relay if faulty.

Good to Know

  • Repeated forced starting with a faulty glow plug can damage the engine (premature wear, fouling).
  • After repair, reset the engine computer to turn off the warning light.

If you don’t have the necessary equipment, consult a specialized diesel mechanic! 🔧

P138D Code: Glow Plug Circuit/Performance Problem (Cylinder 4)

Common Symptoms

  • ❄️ Hard starting in cold weather (engine cranks for a long time before starting),
  • 🚗 Unstable idle or vibrations at startup,
  • ⚡ Misfires (especially when cold),
  • 💡 Engine fault light (Check Engine/ESP) illuminated,
  • 📉 White smoke from exhaust (unburned fuel).

Possible Causes

  1. 🔧 Faulty glow plug (cylinder 4): Internal failure (80% of cases).
  2. 🔌 Electrical issue in cylinder 4 circuit:
    • Cut/oxidized wires between GPCM and glow plug,
    • Defective or corroded connector.
  3. 💻 Control Module (GPCM) failure: Failure of the circuit dedicated to cylinder 4.
  4. ⚡ Faulty power supply:
    • Defective glow plug relay,
    • Blown fuse (check fuse box).

Step-by-Step Diagnosis

  1. 📏 Test glow plug #4:
    • Disconnect its connector,
    • Measure its resistance with a multimeter:
      • Normal value: 0.1 – 2 Ω (check manufacturer specification),
      • Infinite resistance = dead glow plug.
    • Alternative: Use a glow plug tester (red glow = OK).
  2. 🔍 Inspect wiring:
    • Follow the wire from GPCM to cylinder 4,
    • Look for burn marks, cuts, or corrosion.
  3. 🔋 Check power supply:
    • Test voltage at glow plug terminals during startup (should be ~10-12V for 2-10 sec).
  4. 🧩 Check GPCM and relay:
    • Scan the module for associated fault codes (e.g., P138A, P138B, P138C),
    • Test the relay (audible click + continuity).

Recommended Repairs

Faulty Component Action Average Cost
Glow plug #4 faulty Replace glow plug 20-80 €
Damaged wiring Repair wires/connectors 50-150 € (labor)
GPCM failure Replace module 150-400 € (part)
Relay/fuse faulty Replace part 10-40 €

⚠️ Important:

  • Never force start if a glow plug is faulty → risk of damaging the GPCM!
  • Replace glow plugs in sets (if >100,000 km) to avoid repeated failures.
  • Reset ECU after repair (using diagnostic tool).

Common Mistakes to Avoid

  • Neglecting connector sealing (causing oxidation),
  • Forgetting to calibrate GPCM after replacement (requires reprogramming).

ℹ️ Pro tip: If multiple P138x codes appear (e.g., P138C + P138D), the failure likely comes from the GPCM or relay, not the glow plugs!

If diagnosis exceeds your skills, consult a diesel mechanic 🔧. A specific diagnostic tool (e.g., Delphi, Snap-on) is often essential!

Sources: Manufacturer data (PSA, Renault, VAG), WSM, ETKA.

P138E Code: Glow Plug Circuit Problem – Cylinder 5

Key Symptoms

  • 🥶 Very difficult starting (especially below 10°C),
  • 🌫️ Thick white smoke from the exhaust (unburned fuel),
  • 📳 Idle vibrations or intermittent stalling,
  • ⚠️ Check Engine light on (+ possible glow plug light).

Probable Causes (by frequency)

  1. Faulty glow plug (cylinder 5):
    • Resistance out of specification (normal value: 0.1 – 2 Ω),
    • Internal short circuit or open circuit.
  2. Wiring problem (cylinder 5):
    • Cut, chafed, or oxidized wires (especially near the exhaust manifold),
    • Loose/corroded connector.
  3. GPCM Module Failure:
    • Failure of the circuit dedicated to cylinder 5,
    • Module overvoltage/overheating (often caused by a faulty glow plug).
  4. General power supply issue:
    • Stuck/faulty glow plug relay,
    • Blown fuse (check amperage ≥ 40A).

Step-by-Step Diagnosis

1. Test glow plug #5:

  • Disconnect the connector,
  • Measure the resistance between the + terminal and the glow plug ground: ∞ Ω (infinity) → Dead glow plug < 0.1 Ω → Short circuit > 2 Ω → Resistance too high
  • Alternative: Use a glow plug tester (should glow red in 5 sec max).

2. Inspect wiring (priority!):

  • Visually check the wire from GPCM to cylinder 5 (look for melted insulation, corrosion),
  • Test continuity wire by wire (multimeter in Ω mode),
  • Check the supply voltage: 10-12V during glow plug activation.

3. Check GPCM/Relay:

  • Scan the module: associated codes (P138A to P138D) indicate GPCM failure,
  • Test the relay:
    • Audible click upon activation,
    • Continuity between terminals 30-87 when powered.

Recommended Repairs

Failure Solution Estimated Cost
Glow plug #5 faulty Replace the glow plug 25-90 €
Damaged wiring Repair the harness 60-200 €
Defective GPCM Replace + reprogram* 200-500 €
Faulty relay/fuse Replace the part 10-50 €

* Some vehicles require GPCM pairing with the ECU (professional diagnostic tool required).

Common Mistakes to Avoid

  • Replacing the glow plug without checking the wiring → New fault code within 48h,
  • Forgetting to check the circuit ground (corrosion on chassis ground point),
  • Forcing the start with a faulty glow plug → Accelerated GPCM deterioration.

Technical Tips

  1. 🔧 Replace in sets: If >150,000 km, change all glow plugs (avoids cascade failures).
  2. ⚡ GPCM Protection: Always disconnect the battery before working on the circuit.
  3. 💡 Reset: Clear codes after repair + perform a glow plug cycle (without starting) for verification.

⚠️ Warning: On some engines (e.g., BMW M57, Mercedes OM642), accessing cylinder 5 often requires removing parts (particulate filter, piping).

ℹ️ If the code reappears after replacement: Have the GPCM timing/calibration checked (parameter setting via diagnostic tool) or check for a compression leak at cylinder 5 (weakens the glow plug effect).

Consult a diesel specialist if the diagnosis is complex! 🔧