Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Glow Plugs And Glow Plug Control Module (GPCM)
The diesel engine uses glow plugs to assist with cold weather starting and combustion until the cylinder is warm enough to operate normally. The glow plugs are duty cycle controlled and will overheat if constant 12V is applied.
The glow plugs are operated by the Glow Plug Control Module (GPCM). It contains 8 high current smart MOSFET drivers, one for each glow plug. Glow time and intensity are calculated on the basis of CAN signals (rpm, torque, engine coolant temp, air temp and BARO.) The module also contains 3 drivers for the DEF (NOx reductant) heating and thawing system.
Glow Plug and Glow Plug Control Module (GPM)
The GPCM is connected to the ECU via Diesel high speed CAN. All data and diagnostics pass over this nonpublic communication bus. The standard operating voltages for the GPCM are 6.5 volts to 16 volts. Limited operation between 5.5v and 6.5v on the lower range and no operation below 5.5v. Glow function is disabled below 6.5v and above 16.5v.
| DTCs | U0106 - Lost Communication with GPCM P0381 - Glow Plug/Heater Indicator Circuit P064C - Glow Plug Control Module P06DF - Glow Plug Module Memory Checksum Error P138B - Glow Plug Module System Voltage P20C2 - Reductant Heater "C" Control Performance P263C - Glow Plug Driver Performance P06E5 - Glow Plug Control Module 1 Performance P263E - Glow Plug Control Module 1 Over Temperature |
| Monitor Execution | P06DF, P0381 at power up, otherwise continuous |
| Monitor Sequence | None |
| Sensors OK | None |
| Monitoring Duration | ~1 second to register a malfunction |
| Communication lost for > 5 seconds Cluster detects wait to start lamp in wrong state (off when commanded on) Any internal driver circuits detect fault (not switching or over temp) > 1 sec (glow plugs, DEF heaters or relay) RAM checksums do not match expected GPCM main power feed voltage too low / too high / open circuit (< 6.5 volts or > 16 volts) Low voltage detected on the Reductant Heater Circuit "C" < 5 volts |
| DTCs | P0671 - Cylinder 1 Glow Plug Circuit / Open P0672 - Cylinder 2 Glow Plug Circuit / Open P0673 - Cylinder 3 Glow Plug Circuit / Open P0674 - Cylinder 4 Glow Plug Circuit / Open P0675 - Cylinder 5 Glow Plug Circuit / Open P0676 - Cylinder 6 Glow Plug Circuit / Open P0677 - Cylinder 7 Glow Plug Circuit / Open P0678 - Cylinder 8 Glow Plug Circuit / Open P20B9 - Reductant Heater "A" Control Circuit / Open P20BD - Reductant Heater "B" Control Circuit / Open P20C1 - Reductant Heater "C" Control Circuit / Open |
| Monitor Execution | Glow plugs in heating mode. Heaters operational |
| Monitor Sequence | None |
| Sensors OK | None |
| Monitoring Duration | ~1 second to register a malfunction |
| Individual glow plug circuit current < 1 A, Individual reductant heater circuit current <.2 A |
| DTCs | P066B - Cylinder 1 Glow Plug Circuit High P066D - Cylinder 2 Glow Plug Circuit High P066F - Cylinder 3 Glow Plug Circuit High P067B - Cylinder 4 Glow Plug Circuit High P067D - Cylinder 5 Glow Plug Circuit High P067F - Cylinder 6 Glow Plug Circuit High P068D - Cylinder 7 Glow Plug Circuit High P068F - Cylinder 8 Glow Plug Circuit High P20BC - Reductant Heater "A" Control Circuit High P20C0 - Reductant Heater "B" Control Circuit High P20C4 - Reductant Heater "C" Control Circuit High |
| Monitor Execution | Glow plugs in heating mode. Heaters operational |
| Monitor Sequence | None |
| Sensors OK | None |
| Monitoring Duration | ~1 second to register a malfunction for glow plugs 250 ms to register a malfunction for the reductant heaters |
| Individual glow plug circuit = 0 Amps current, Individual reductant heater circuit = 0 Amps current |
| DTCs | P066A - Cylinder 1 Glow Plug Circuit Low P066C - Cylinder 2 Glow Plug Circuit Low P066E - Cylinder 3 Glow Plug Circuit Low P067A - Cylinder 4 Glow Plug Circuit Low P067C - Cylinder 5 Glow Plug Circuit Low P067E - Cylinder 6 Glow Plug Circuit Low P068C - Cylinder 7 Glow Plug Circuit Low P068E - Cylinder 8 Glow Plug Circuit Low P20BB - Reductant Heater "A" Control Circuit Low P20BF - Reductant Heater "B" Control Circuit Low P20C3 - Reductant Heater "C" Control Circuit Low |
| Monitor Execution | Glow plugs heating mode. Heaters operational. |
| Monitor Sequence | None |
| Sensors OK | None |
| Monitoring Duration | ~3 second to register a malfunction for glow plugs 250 ms to register a malfunction for the reductant heaters |
| Individual glow plug circuit > 20 Amps current > 1 second Individual glow plug circuit > 70 Amps current for >.2 ms Reductant heater relay (circuit "A" & "B") > 15 Amps current > 250 ms Reductant heater relay (circuit "C") > 6 Amps current > 250 ms |
| DTCs | P06B9 - Cylinder 1 Glow Plug Circuit Range / Performance P06BA - Cylinder 2 Glow Plug Circuit Range / Performance P06BB - Cylinder 3 Glow Plug Circuit Range / Performance P06BC - Cylinder 4 Glow Plug Circuit Range / Performance P06BD - Cylinder 5 Glow Plug Circuit Range / Performance P06BE - Cylinder 6 Glow Plug Circuit Range / Performance P06BF - Cylinder 7 Glow Plug Circuit Range / Performance P06C0 - Cylinder 8 Glow Plug Circuit Range / Performance |
| Monitor Execution | Glow plugs in heating mode. |
| Monitor Sequence | After open circuit, short to battery and short to ground testing |
| Sensors OK | None |
| Monitoring Duration | ~ 3 seconds to register a malfunction |
| Individual circuit > 2 ohms resistance |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.