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.
Test Procedure
- AF1 PRELIMINARY DIAGNOSIS
- Clear the PCM DTCs.
- Carry out the KOER Glow Plug Monitor self-test.
Are DTCs P066A, P066B, P066C, P066D, P066E, P066F, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P067A, P067B, P067C, P067D, P067E, P067F, P068C, P068D, P068E, P068F, P06B9, P06BA, P06BB, P06BC, P06BD, P06BE, P06BF, P06C0, P06DF, P06E5, P138B, P263C, U0074 or U0106 present?
Yes No For DTCs U0074 or U0106, GO to AF10.
For DTCs P06DF or P06E5, GO to AF13.
For all others, GO to AF2.For symptoms without DTCs, GO to AF2.
For all others, RETURN to SYMPTOM CHARTS for further direction. - AF2 REPROGRAM THE GPCM OR UPDATE THE GPCM CALIBRATION NOTE: Wait for 2 minutes before disconnecting the GPCM connectors.
- Ignition OFF.
- For Transit,
- GPCM-A connector disconnected.
- GPCM-B connector disconnected.
- Visually inspect for:
- pushed out pins
- corrosion
- damaged seals
- GPCM-A connector connected.
- GPCM-B connector connected.
- Make sure the GPCM connectors are seated correctly.
- Ignition ON, engine OFF.
- Clear the PCM DTCs.
- Carry out the PCM self-test.
- If any glow plug DTCs are retrieved again, turn the ignition OFF and wait for 2 minutes.
- Clear the PCM DTCs.
- Carry out the PCM self-test.
- For all others,
- GPCM-A connector disconnected.
- GPCM-B connector disconnected.
- GPCM-C connector disconnected.
- Visually inspect for:
- pushed out pins
- corrosion
- damaged seals
- GPCM-A connector connected.
- GPCM-B connector connected.
- GPCM-C connector connected.
- Make sure the GPCM connectors are seated correctly.
- Ignition ON, engine OFF.
- Clear the PCM DTCs.
- Carry out the KOER Glow Plug Monitor self-test.
- If any glow plug DTCs are retrieved again, turn the ignition OFF and wait for 2 minutes.
- Reprogram the GPCM or update the GPCM calibration.
- Clear the PCM DTCs.
- Carry out the KOER Glow Plug Monitor self-test.
Are any glow plug DTCs retrieved again?
Yes No For DTCs P138B and P263C, GO to AF4.
For all others, GO to AF3.The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. - AF3 CHECK THE SUSPECT GLOW PLUG RESISTANCE NOTE: Use the component connector information to match the connector pins with the DTCs.
- Ignition OFF.
- Glow Plug connector disconnected.
- Check for loose, damaged, or backed out terminals.
- Measure the resistance between:
(+) Glow Plug Connector, Component Side (-) Suspect Glow Plug Ground
Is the resistance less than 2 ohms?
Yes No GO to AF4. For Transit, INSTALL a new Glow Plug.
REFER to the appropriate Glow Plug System.
Clear the PCM DTCs. REPEAT the self-test.
For all others, INSTALL a new Glow Plug.
REFER to the appropriate Glow Plug System. Carry out the KOER Glow Plug Monitor self-test.
Clear the PCM DTCs. REPEAT the self-test. - AF4 CHECK THE VBATT CIRCUIT FOR VOLTAGE NOTE: Wait for 2 minutes before disconnecting the GPCM connectors.
- Ignition OFF.
- GPCM-A connector disconnected.
- Ignition ON, engine OFF.
- Measure the voltage between:
(+) GPCM-A Connector, Harness Side (-) VBATT Ground
Is the voltage greater than 10.5 V?
Yes No For DTCs P138B and P263C, GO to AF8.
For all others, GO to AF5.REPAIR the open circuit. Clear the PCM DTCs.
REPEAT the self-test. - AF5 CHECK THE GLOW PLUG CIRCUIT FOR AN OPEN NOTE: Wait for 2 minutes before disconnecting the GPCM connectors.
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.