Code P0671: Explanations, Symptoms, and Solutions
Meaning of Code P0671
Code P0671 is a generic OBD-II code related to a malfunction in the glow plug circuit for cylinder #1 in diesel engines. This code indicates that the Powertrain Control Module (PCM) has detected a problem in the electrical circuit or an abnormal resistance of the glow plug in cylinder 1.
Role of Glow Plugs:
- 🔥 Heat the cylinder head to facilitate cold starts by increasing combustion temperature.
- ⚡ Assist in fuel ignition in diesel engines, which rely on compression to ignite the fuel.
Severity of Code P0671
| Severity Level | Potential Risks |
|---|---|
| Moderate |
- ❄️ Difficult starting in cold weather.
- 📉 Loss of power or misfires.
- ⚠️ Engine damage if multiple glow plugs are faulty.
Recommended Action:
Although a single faulty glow plug may not prevent starting, prompt diagnosis is necessary to avoid worsening problems.
Common Symptoms
- 🚨 Illuminated check engine light.
- ❄️ Difficult or impossible starting in cold weather.
- 📉 Reduced power until the engine warms up.
- 🔧 Misfires or hesitation during acceleration.
- ⚡ Inactive glow plug light (does not turn off).
Possible Causes
- Faulty glow plug: Resistance out of specification (0.5 to 2.0 Ω).
- Electrical problem:
- Damaged wires, cracked insulation, or oxidized connectors.
- Short circuit or open circuit in the wiring harness.
- Control module failure: Faulty relay or glow plug module.
- Corrosion: Due to moisture or extreme conditions.
Diagnostic and Repair Steps
Required Tools:
- 📟 OBD2 scan tool to clear codes.
- 🔌 Digital multimeter (DVOM) to measure resistance and continuity.
- 🔧 Appropriate wrenches to remove the glow plug (depending on the model).
Step 1: Check for Related Codes
- If code P0670 (glow plug control circuit malfunction) is present, diagnose it first.
Step 2: Visual Inspection
- Locate the glow plug for cylinder #1.
- Check the connector and wire:
- Look for signs of corrosion, burning, or disconnection.
- Ensure the wire is not chafed or damaged.
Step 3: Measure Glow Plug Resistance
- Disconnect the glow plug connector.
- Set the multimeter to ohmmeter (Ω) mode.
- Measure the resistance between the glow plug terminal and ground:
- Normal value: 0.5 to 2.0 Ω (check manufacturer specifications).
- If out of range: Replace the glow plug.
Step 4: Test the Electrical Circuit
- Check continuity between the relay bus bar and the glow plug:
- Place one probe on the bus bar (relay side) and the other on the glow plug wire.
- Resistance should be ≤ 2 Ω. If higher, replace the wire.
- Inspect the fuse links on the bus bar.
Step 5: Test the Control Module
- Use an advanced diagnostic tool to activate the glow plug relay.
- Check the supply voltage (typically 12 V) on the circuit.
- If the module does not respond, suspect an internal failure.
Step 6: Reset and Test
- Clear the code with the OBD2 tool.
- Perform a road test in cold weather to confirm the repair.
Good to Know
- ⚠️ Do not overload the glow plugs: Prolonged activation can cause them to melt.
- 🔄 Group replacement: On high-mileage vehicles, replace all glow plugs to avoid imbalances.
- 🌡️ Cold weather impact: This code is more common in winter. A faulty glow plug will make starting nearly impossible at -10°C or lower.
Conclusion
Code P0671 is often related to a worn glow plug or an electrical circuit issue. Although the engine may start with one faulty glow plug, prompt diagnosis is crucial to maintain performance and reliability. If you are not comfortable with electrical testing, consult a certified diesel mechanic.
🔧 Recommended Parts: OEM glow plugs, replacement wiring harness if necessary.