The P0684: Glow Plug Control Module to PCM Communication Circuit Range/Performance code indicates a performance issue in the communication circuit between the Glow Plug Control Module and the Powertrain Control Module (PCM). This communication ensures that the glow plugs are activated correctly, particularly during cold starts. If the communication circuit is not functioning properly, it may result in hard starts or failure to start.
P0684 – Quick Overview
| Code | Information |
|---|---|
| Meaning | P0684: Glow Plug Control Module to PCM Communication Circuit Range/Performance |
| Is it serious? | Yes, as improper communication between the PCM and Glow Plug Control Module can lead to engine starting problems, especially in cold weather. |
| Possible causes | – Performance issue in the communication circuit between glow plug control module and PCM – Faulty communication circuit – Faulty glow plug control module or PCM |
| How to diagnose? | – Test performance of communication circuit between glow plug control module and PCM – Inspect wiring and connectors – Replace glow plug control module or PCM if necessary |
P0684 Meaning
The P0684 code indicates that the communication circuit between the Glow Plug Control Module and PCM is not performing as expected. This issue can cause the glow plugs to function improperly, leading to engine starting difficulties, especially in colder climates. The problem may be caused by poor signal quality, wiring issues, or malfunctioning control modules.
Step-by-step diagnostic guide
| Action | Description | Tools Needed |
|---|---|---|
| Check for Other Codes | Use an OBD-II scanner to check for additional related codes, especially those related to the PCM or Glow Plug Control Module that could provide more insight. | OBD-II Scanner |
| Test the Communication Circuit for Performance | Use a multimeter to measure the performance of the communication circuit between the Glow Plug Control Module and the PCM. Verify that the voltage and signal range are within manufacturer specifications. | Multimeter |
| Inspect Wiring and Connectors | Inspect all wiring and connectors between the Glow Plug Control Module and PCM for damage, corrosion, or loose connections that could impact performance. | Flashlight, Multimeter |
| Test the Glow Plug Control Module | Use a diagnostic tool to ensure that the Glow Plug Control Module is communicating properly with the PCM. Replace the module if it is underperforming or faulty. | Diagnostic Tool, Multimeter |
| Test the PCM | If necessary, test the PCM to confirm it is receiving and sending proper signals to the Glow Plug Control Module. Replace the PCM if it is not functioning correctly. | Diagnostic Tool, Multimeter |
| Replace the Glow Plug Control Module or PCM if Necessary | If the Glow Plug Control Module or PCM is malfunctioning and cannot be repaired, replace the necessary component to restore proper communication and performance. | Replacement Module, Tools |
| Clear the Code and Test | After repairs, clear the code using an OBD-II scanner and test the vehicle to ensure the Glow Plug Control Module and PCM are communicating properly. | OBD-II Scanner, Vehicle Manual |
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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