What is the P0115 Code?

The generic diagnostic trouble code (DTC) P0115 indicates a malfunction in the Engine Coolant Temperature (ECT) sensor circuit. This code applies to all vehicles equipped with the OBD-II standard (from 1996 onwards). Troubleshooting procedures may vary slightly depending on the make and model.

ECT Sensor Operation

The ECT (Engine Coolant Temperature) sensor is a thermistor whose resistance changes with temperature. It is typically a two-wire sensor: one wire receives a 5-volt reference voltage from the Powertrain Control Module (PCM), and the other sends a return signal to the PCM.

Note: This sensor is separate from the temperature sender that powers the dashboard gauge, although their operating principle is similar.

When the engine is cold, the sensor’s resistance is high. When it is hot, the resistance is low. The PCM continuously monitors this value. If the signal voltage falls outside the expected ranges (too high or too low), the P0115 code is stored and the Malfunction Indicator Lamp (MIL) illuminates.

Symptoms of the P0115 Code

A P0115 code may present with several symptoms:

• Illumination of the Malfunction Indicator Lamp (MIL)
• Difficult vehicle starting
• Excessive black smoke from the exhaust (overly rich mixture)
• Unstable idle, stalling
• Poor cooling fan operation (continuous running or failure to operate)
• Possible increase in NOx emissions (detectable with a gas analyzer)

Possible Causes of the Fault

The most common causes of a P0115 code are:

• Faulty ECT sensor
• Damaged wiring or corroded/faulty connector
• Short circuit or open circuit in the reference (5V) wire or signal (ground) wire
• Internal PCM problem (less common)

How to Diagnose and Repair the P0115 Code?

Here is a step-by-step troubleshooting procedure to identify and resolve the cause of the P0115 code.

Step 1: Visual Inspection

Visually inspect the sensor, its connector, and the wiring. Look for signs of damage, corrosion, or loose wires. Repair or replace as necessary.

Step 2: Verification with a Diagnostic Tool

Using an OBD-II scanner, read the displayed coolant temperature.

• If the reading is abnormally high (e.g., ~140°C / 280°F): Disconnect the sensor connector. If the reading drops sharply (e.g., to -45°C / -50°F), the sensor is likely internally shorted and should be replaced. If the reading remains high, there is a short to ground in the signal wiring.
• If the reading is abnormally low (e.g., -45°C / -50°F): Check for the presence of the 5V reference voltage at the sensor connector (engine off, ignition on). If it is absent, check the circuit back to the PCM. If it is present, the sensor or the signal circuit may be open.

Step 3: Electrical Tests

To confirm the sensor’s condition, measure its resistance with a multimeter and compare it to the manufacturer’s reference values for the current engine temperature. Infinite resistance (open circuit) or zero resistance (short circuit) indicates a faulty sensor.

Step 4: PCM Verification

If all circuits and the sensor are in good condition, an internal PCM fault is possible, although rare.

Conclusion and Call to Action

The P0115 code is often resolved by replacing the ECT sensor, a typically inexpensive part. However, accurate diagnosis helps avoid unnecessary part replacements.

Experiencing this issue? If you do not have the necessary tools or skills, it is recommended to entrust the diagnosis to a professional mechanic for a reliable repair.

Related codes: P0115, P0116, P0117, P0118, P0119, P0125, P0128

Code P0116: Definition and Explanations

The error code P0116 is a generic powertrain code. It indicates a problem with the range or performance of the ECT (Engine Coolant Temperature) sensor circuit. This generic code applies to most vehicles built after 1996 (Ford, Hyundai, Kia, Mazda, Mercedes-Benz, etc.). Although common, specific diagnostic procedures may vary depending on the vehicle’s make and model.

Role and Operation of the ECT Sensor

The ECT sensor is a thermistor, a component whose electrical resistance varies depending on the temperature of the coolant it is in contact with. It is typically located in the engine block or on a coolant passage. It is usually a two-wire sensor:

• One wire receives a 5-volt reference voltage from the PCM (Powertrain Control Module).
• The other wire provides a ground signal to the PCM.

When the temperature changes, the sensor’s resistance changes, thus altering the voltage of the signal sent back to the PCM. The PCM interprets this voltage to determine the engine’s exact temperature, a crucial piece of information for managing fuel, ignition, and idle.

The PCM expects a slow and gradual change in this signal, consistent with the engine’s normal warming up. The P0116 code is triggered when the PCM detects a voltage variation that is too rapid, illogical, or shows no variation at all, which does not match the engine’s thermal reality.

Symptoms of Code P0116

Symptoms may be absent if the problem is intermittent, but they generally include:

• Illumination of the Malfunction Indicator Lamp (MIL) on the dashboard.
• Poor drivability and loss of engine performance.
• Black smoke from the exhaust (overly rich mixture).
• Increased fuel consumption.
• Problems with unstable idle or engine stalling.
• Engine misfires.

Possible Causes of the P0116 Fault

Several elements can be the cause of this code:

• A faulty, missing, or stuck-open thermostat.
• A faulty ECT sensor.
• A short circuit or open circuit in the signal or ground wire.
• Oxidized, loose, or corroded electrical connections.
• An internal problem with the PCM (rare).

Diagnosis and Solutions for Resolving P0116

Warning: If other codes related to the ECT sensor (such as P0115, P0117, P0118, P0119, P0125, P0128) are present, diagnose them first.

Step 1: Checking Live Data

Using an OBD2 diagnostic tool, observe the live data reading of the coolant temperature on a cold engine. It should be close to the ambient temperature and roughly match the reading from the Intake Air Temperature (IAT) sensor.

Step 2: Analyzing Freeze Frame Data

Check the data recorded at the time of the fault (Freeze Frame). This will tell you the precise value of the ECT sensor when the code was stored.

• If the indicated value is extremely low (e.g., -40°C / -40°F): This suggests an excessively high and intermittent resistance. Check the signal circuit for an open circuit or poor connection. If the wiring is intact, the ECT sensor is likely faulty.
• If the indicated value is extremely high (e.g., > 150°C / 300°F): This suggests an excessively low resistance. Look for a short to ground on the signal circuit. If the wiring is good, replace the ECT sensor.

Step 3: Testing the Sensor and Circuit

To confirm:

1. Measure the resistance of the ECT sensor when cold and when hot using a multimeter. Compare the obtained values with those specified by the manufacturer.
2. Visually inspect the sensor’s connector and wiring for any signs of corrosion, damage, or looseness.
3. Check the condition and operation of the thermostat.

Conclusion and Call to Action

The P0116 code is often resolved by replacing a faulty ECT sensor or repairing a damaged wire. Accurate diagnosis with a scan tool is essential to avoid replacing parts unnecessarily.

Experiencing this issue? Share your experience or ask your questions in the comments below. For complex diagnostics, do not hesitate to consult a professional mechanic equipped with the appropriate tools.

What is the P0117 Code?

The P0117 trouble code is a generic powertrain code that indicates a low input from the Engine Coolant Temperature (ECT) sensor circuit. It applies to most vehicles built after 1996 (Honda, Toyota, Volkswagen, Ford, etc.). Although generic, specific diagnostic procedures may vary by make and model.

Role and Operation of the ECT Sensor

The Engine Coolant Temperature (ECT) sensor is a thermistor located in the engine block or a coolant passage. Its electrical resistance varies with the coolant temperature. It is typically a two-wire sensor: one receives a 5-volt reference voltage from the Powertrain Control Module (PCM), and the other serves as ground.

When the engine is cold, the sensor’s resistance is high. When it is hot, its resistance is low. The P0117 code is triggered when the PCM detects an abnormally low signal voltage, indicating an excessively “hot” condition.

Symptoms of the P0117 Code

• Malfunction Indicator Lamp (MIL) illuminated
• Poor fuel economy
• Engine misfiring or stalling
• Rough or impossible idling
• Black smoke from the exhaust
• Hard starting or stalling after starting

Possible Causes

• Faulty ECT sensor
• Short to ground in the signal circuit
• Oxidized, damaged, or loose connectors
• Damaged or chafed wiring harness
• 5V reference issue from the PCM
• Engine overheating (rare)
• Faulty PCM (very rare)

Diagnosis and Solutions

The P0117 code indicates an abnormal “hot” condition. The first step is to determine whether the problem is with the sensor, the wiring, or, more rarely, actual overheating.

Step 1: Verification with a Diagnostic Tool

With the ignition on (engine off, KOEO), observe the ECT sensor temperature reading on the diagnostic tool. On a cold engine, it should be close to ambient temperature and match the Intake Air Temperature (IAT) sensor reading. A significant discrepancy indicates a likely issue with the ECT sensor.

Step 2: Testing the Sensor and Wiring

If the reading shows an excessively hot temperature (e.g., > 125°C), disconnect the ECT sensor connector. The reading on the diagnostic tool should drop to an extreme cold value (e.g., -40°C).

• If the reading drops: The ECT sensor has an internal short circuit. It must be replaced.
• If the reading does not change: There is a short to ground in the wiring between the sensor and the PCM. Visually inspect the harness for signs of wear, chafing, or melting. Repair or replace the damaged wiring.

Step 3: Checking the 5V Reference Circuit

If the wiring appears intact, check the voltage at the signal wire pin on the PCM connector. An absent or low voltage may indicate a PCM issue or a short on the 5-volt reference circuit shared with other sensors. If other sensor codes are present, disconnect the sensors one by one to identify the one causing the short.

Step 4: Intermittent Issue

If the reading seems normal, the problem may be intermittent. Shake the wiring harness and manipulate the connectors while monitoring the ECT reading. Use the “freeze frame data” function of your diagnostic tool to see the value recorded at the time of the fault.

Related Codes

P0115, P0116, P0118, P0119, P0125, P0128

What is the P0118 Code?

The P0118 trouble code is a generic powertrain code. It indicates that the Powertrain Control Module (PCM) has detected an abnormally high voltage in the Engine Coolant Temperature (ECT) sensor circuit. This code applies to most vehicles built from 1996 onwards (Honda, Toyota, Volkswagen, Ford, BMW, etc.). Although generic, specific diagnostic procedures may vary by make and model.

ECT Sensor Operation

The ECT sensor is a thermistor located in a coolant passage, typically on the engine cylinder head. Its principle is simple: its electrical resistance is high when the engine is cold and decreases as the coolant temperature rises.

The PCM sends a 5-volt reference voltage to the sensor and monitors the return voltage. This measurement allows it to calculate the temperature in real-time. If the received signal indicates a constantly very low temperature (below freezing) when the engine is hot, or if the resistance is out of specifications, the PCM logs the P0118 code and illuminates the Malfunction Indicator Lamp (MIL).

Symptoms of the P0118 Code

A fault in the ECT sensor circuit can cause several symptoms:

• ⛽ Poor fuel economy: The PCM, receiving incorrect information, excessively enriches the air-fuel mixture.
• 🚗 Starting problems: Difficulty starting when cold or hot.
• ⚡ Poor engine performance: Rough idle, hesitation, misfires, and black smoke emissions.
• ⚠️ Warning light: Illumination of the check engine light on the dashboard.

Possible Causes of the Fault

Several elements can be the cause of the P0118 code:

• 🔌 Connection problem: Loose, corroded, or oxidized sensor connector.
• ⚡ Circuit problem: Short to voltage in the signal wire between the sensor and the PCM, or an open ground circuit.
• 🔧 Faulty sensor: Internally shorted ECT sensor (most common cause).
• 🤖 PCM failure: An internal problem with the control module is rare but possible.

Diagnosis and Solutions

To diagnose and resolve a P0118 code, follow this step-by-step procedure:

1. Verification with a Diagnostic Tool

Connect an OBD2 scan tool and observe the live temperature value displayed. If it is logical (increases gradually as the engine warms up), the problem is likely intermittent. Wiggle the sensor harness and connector while monitoring the scan tool. A sudden drop in the reading confirms a bad connection.

2. Sensor Test

If the reading is illogical (e.g., constant -40°C), unplug the sensor and measure its resistance with a multimeter. Compare the measured value to the manufacturer’s specifications for ambient temperature. An out-of-spec resistance indicates a faulty sensor that needs replacement.

3. Circuit Test

If the sensor seems good, the problem is in the circuit. With the engine off, disconnect the sensor connector. Using a jumper wire, short the two pins of the connector on the harness side. If the scan tool now displays a very high temperature (above 120°C), the circuit and PCM are functional, confirming the sensor is faulty.

4. Voltage and Ground Check

With the ignition on, use the multimeter to check for the presence of the 5V reference voltage and a good ground at the sensor connector (wires disconnected).

• If the 5V and ground are absent at the connector, check for their presence directly at the PCM connector.
• If they are present at the PCM, there is a break or short in the wiring that needs repair.
• If the 5V is absent at the PCM even after disconnecting the connector, the PCM is likely faulty.

Important Note: Although a bad sensor is the most common cause of the P0118 code, it is essential to check the circuit before replacing it to avoid an ineffective repair. If you are not comfortable with these electrical procedures, entrust the diagnosis to a professional mechanic.

Related Codes

Codes related to the engine coolant temperature sensor circuit: P0115, P0116, P0117, P0119, P0125, P0128.

Definition of Code P0119

The trouble code P0119 is a generic OBD-II code from the powertrain group. It indicates a problem with the Engine Coolant Temperature (ECT) sensor circuit, manifesting as an intermittent or erratic signal sent to the engine control module (PCM or ECU).

Role of the Engine Coolant Temperature Sensor

• Function: Precisely measure the coolant temperature to allow the PCM to regulate essential functions:
  • The air-fuel mixture (rich when cold, lean when hot).
  • Ignition timing.
  • Idle speed.
  • Activation and speed of the cooling fan.
  • Regeneration of the diesel particulate filter (DPF) or EGR valve on some engines.
• Technical Principle: It is a Negative Temperature Coefficient (NTC) thermistor. Its electrical resistance decreases as the coolant temperature increases. The PCM sends a reference voltage (usually 5V) and interprets the returned voltage to determine the temperature.
• Sensor Types:
  • 2-wire: Reference voltage (5V) and ground (signal for the PCM).
  • 3-wire: Adds a dedicated wire to power the dashboard gauge.

Symptoms of Code P0119

• 🚨 Check Engine Light illuminated (MIL) on the dashboard.
• ❄️ Very unstable idle, especially during a cold start.
• ⚠️ Hesitation, stumbling, and power loss during acceleration.
• ⛽ Excessive fuel consumption and smell of gasoline (overly rich mixture).
• 🌡️ Cooling system malfunction: Cooling fan running continuously or not at all, risk of engine overheating.
• ⚠️ Difficulty starting in cold weather.

Possible Causes of Code P0119

Electrical and Mechanical Problems

1. Faulty ECT Sensor: The thermistor is damaged, providing a resistance value outside the manufacturer’s specifications.
2. Wiring Problems:
   • Cut, frayed, or chafed electrical wires.
   • Short circuits or faulty ground connections.
   • Oxidized, loose, or corroded connectors (caused by coolant leaks).
3. Low Coolant Level: A leak in the system can prevent the sensor from being properly immersed, skewing its reading.
4. Faulty Thermostat: If it remains stuck open, the engine never reaches its optimal operating temperature, disrupting the system.
5. Problem with the PCM: Although rare, an internal fault in the control module can be the cause.

Diagnosis and Repair Procedure

Required Tools

• OBD2 scanner to read codes and live data.
• Digital multimeter (DVOM) to measure resistance and voltage.
• Infrared thermometer to check the actual engine temperature.
• Basic tool kit, coolant, and contact cleaner spray.

Diagnostic Steps

1. Preliminary Checks: Check the coolant level and condition. Look for any obvious signs of leaks.
2. Visual Inspection: Carefully inspect the ECT sensor wiring and connector along their entire length. Look for physical damage, corrosion, or loose pins. Clean the connectors.
3. Test with OBD2 Scanner:
   • Read the live data. Compare the temperature value displayed by the sensor with the actual engine temperature measured with the infrared thermometer on the thermostat or radiator.
   • A significant discrepancy or an erratic, jumping value indicates a problem.
4. Electrical Tests (engine cold and disconnected):
   • Resistance Test: Measure the resistance between the sensor pins. Compare it to the manufacturer’s reference values (e.g., ~2000-3000 Ω at 20°C). An infinite value (open circuit) or zero (short circuit) confirms a faulty sensor.
   • Voltage Test: Reconnect the connector, ignition on. Measure the voltage between the signal wire and ground. It should be around 3V when cold and gradually decrease as the engine warms up.

Repair

• Replacing the ECT Sensor:
  1. Locate its position (usually on the engine block, cylinder head, intake manifold, or thermostat housing).
  2. Turn the ignition OFF. Disconnect the electrical connector.
  3. Carefully unscrew the old sensor. A small coolant leak is normal; catch it.
  4. Screw in the new sensor (use a new seal if necessary). Reconnect the connector.
• Repairing the Wiring: Solder and use heat-shrink tubing or replace damaged wire sections.
• Refilling Coolant: After replacement, top up the level with the appropriate mixture (often 50/50) and bleed the system of air.

Validating Repairs

1. Clear the trouble codes with the scanner.
2. Start the cold engine and let it warm up to normal operating temperature.
3. Monitor the scanner data: the temperature should rise progressively and stabilize around 90°C.
4. Perform a road test to verify that the symptoms (unstable idle, hesitation) have disappeared and that the Check Engine Light does not come back on.

Important Recommendations and Precautions

• 🔧 Priority: Do not ignore this code. A faulty signal can lead to severe overheating, damage the catalytic converter, and increase engine wear.
• ⚠️ Quality Parts: Prefer OEM quality or reputable brand sensors. Low-end parts often have an imprecise resistance curve and can cause the code to reappear.
• 🧤 Safety: Never open a radiator cap on a hot engine. Risk of severe burns. Handle coolant with gloves.
• 📄 Related Codes: Also diagnose codes P0115, P0116, P0117, or P0118 if present, as they relate to the same circuit.

References: Always consult your vehicle’s repair manual for precise resistance values and specifications.