The OBD2 code P0380 indicates a malfunction within the glow plug/heater circuit “A,” highlighting issues with the system responsible for warming the engine’s cylinders in diesel vehicles. This pre-heating is essential for cold starts by improving combustion efficiency when the engine is cold. Faults in this circuit can lead to starting difficulties, especially in cold weather, and may trigger the “check engine” light.
P0380 quick overview
| Meaning | P0380: Glow Plug/Heater Circuit “A” Malfunction |
| Is it serious? | Yes, it can significantly affect the vehicle’s ability to start in cold temperatures and impact overall engine performance. |
| Possible causes | – Faulty glow plugs – Malfunctioning glow plug relay or module – Wiring or connector issues in the glow plug circuit – Problems with the engine control module (ECM) |
| How to diagnose? | Inspect glow plugs for proper operation and replace if necessary Test the glow plug relay/module for correct functioning Check the wiring and connectors for damage, corrosion, or loose connections Evaluate the ECM for any related fault codes or issues |
P0380 Meaning
For those who might not be as familiar with diesel engines, think of glow plugs as small electric heaters that warm up the engine’s combustion chambers, making it easier to start the engine in cold weather. When you see a P0380 code, it means there’s a problem in the electrical system that controls these heaters, which could make your car hard to start on chilly mornings.
Fixing this issue might involve replacing one or more glow plugs, fixing a relay that controls them, or repairing damaged wires in the circuit. It’s a bit like repairing a faulty electric heating system in your house to ensure it’s ready to keep you warm when winter comes.
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How to fix P0380 – learn from mechanics
I looked into P0380 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Mercedes with P0380
Vehicle Information 1998 Mercedes-Benz E300 3.0L
Issue + Repair History
- “Check engine” warning lamp illuminated.
- Glow plug lamp lights, then goes out at start, but comes back on after running for a few seconds.
- No starting or drivability symptoms reported.
- Scanner used: Launch x-431 scanner, Snap-On brick under OBD-II generic.
- P0380 code detected, undefined.
- Previous scanner lacked diesel engine capability.
- Glow plug relay replaced.
- All 6 glow plugs replaced.
Other OBD2 Codes + Test Results
- P0380: Undocumented code/undefined.
- Diagnostic tests performed:
- Resistance test of glow plugs.
- Check for voltage at glow plug module connector.
Mechanic Suggestions
- Replace glow plugs and pre-glow relay as both can cause the symptoms observed.
- Conduct resistance test on glow plugs individually.
- Test for voltage at pin 3 of the glow plug module connector.
- Check for communication wire between engine control module and preglow control module.
- Consider using specialized diagnostic tools for European cars.
Final Fix
- Replaced all 6 glow plugs and pre-glow relay, resolving both “check engine” and glow plug warning lamps.
Case #2: Volkswagen P0380
Vehicle Information 2000 Volkswagen Jetta TDI 1.9L
Issue + Repair History
- MIL lamp illuminated.
- Fault code P0380 detected.
- MAF sensor replaced approximately 20k miles ago.
- Recent service: air, fuel filters replaced.
Other OBD2 Codes + Test Results
- P0380: Undocumented code.
- Glow plug circuit fault detected.
- Glow plug relay and glow plugs tested.
- Glow plug resistance test conducted.
- Power at glow plug wires confirmed.
Mechanic Suggestions
- Check glow plug relay and glow plugs for faults.
- Use test light to check continuity of glow plugs.
- Verify voltage at glow plug module connector.
- Consider using specialized diagnostic tools for Volkswagen.
- Check for communication wire between engine control module and glow plug control module.
Final Fix
- Replaced all glow plugs after finding slight resistance variation in one of them.
- The MIL lamp was off for 1 week following the repair.
Case #3: Chevrolet P0380
Vehicle Information 2001 Chevrolet Silverado 2500 HD LS 6.6L
Issue + Repair History
- Check engine light illuminated with code P0380.
- No starting problems experienced throughout the winter.
- Voltage checked at large red wire at controller – good.
- Other two large terminals checked for power.
- One terminal powers up with key on and when intake heater is activated with scan tool.
- Other terminal has no power even when glow plugs are activated with scan tool.
Other OBD2 Codes + Test Results
- P0380: Glow plug feedback circuit fault.
- Glow plug controller replaced.
- Continuity tested through each glow plug to ground, 7 out of 8 glow plugs had continuity, one did not.
- Cylinder #3 glow plug found to be faulty.
- Glow plug replaced and PCM cleared.
- Test drive conducted with no codes returned.
Mechanic Suggestions
- Check continuity through each glow plug to ground.
- Replace any faulty glow plugs detected during continuity test.
- Check 175-amp battery fuse and circuit 506 for open circuits.
- Investigate potential wiring issues in the glow plug circuit or a faulty PCM.
- Ohm test the glow plugs for proper resistance.
- Consider air leaks in the fuel injection control module (FICM) causing extended crank or no start conditions.
Final Fix
- Replaced glow plug controller.
- Replaced faulty glow plug in cylinder #3.
- PCM cleared and test drive conducted without codes returning.
How to diagnose P0380
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Explanation |
|---|---|
| Inspect glow plugs | Check for wear or damage and replace as necessary. |
| Test the glow plug relay/module | Ensure it activates the glow plugs appropriately. |
| Check the wiring and connectors | Look for signs of damage or loose connections in the circuit. |
| Evaluate the ECM | Check for any fault codes that might indicate a related issue. |
Addressing a P0380 code involves a thorough examination of the glow plug system, ensuring all components function correctly to facilitate smooth engine starts in cold conditions. Given the importance of glow plugs in diesel engines, particularly during the colder months, resolving this issue promptly is crucial for reliable vehicle operation.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko