The P0687: ECM/PCM Power Relay Control Circuit High code indicates that the control module has detected a higher-than-expected voltage in the power relay control circuit for the ECM (Engine Control Module) or PCM (Powertrain Control Module). This can cause issues with proper control module function, leading to engine performance problems. High voltage may result from a faulty relay, wiring issues, or a malfunction in the control circuit.
P0687 – Quick Overview
| Code | Information |
|---|---|
| Meaning | P0687: ECM/PCM Power Relay Control Circuit High |
| Is it serious? | Yes, as it can lead to improper ECM/PCM function and engine performance issues. |
| Possible causes | – High voltage in ECM/PCM power relay control circuit – Faulty relay – Wiring issue |
| How to diagnose? | – Test ECM/PCM power relay control circuit for voltage – Inspect wiring and connectors – Replace relay if necessary |
P0687 Meaning
The P0687 code means that the ECM or PCM is receiving a higher-than-expected voltage in the power relay control circuit. This high voltage can cause the control modules to malfunction, resulting in poor engine performance or failure to start. High voltage in the circuit can be caused by a faulty power relay or wiring issues.
Step-by-step diagnostic guide
| Action | Description | Tools Needed |
|---|---|---|
| Check for Other Codes | Use an OBD-II scanner to check for other related codes, especially those involving the ECM or PCM, which may provide more context for the issue. | OBD-II Scanner |
| Test the ECM/PCM Power Relay Control Circuit for Voltage | Use a multimeter to measure the voltage in the ECM/PCM power relay control circuit. Compare the readings with the manufacturer’s specifications to check for high voltage. | Multimeter |
| Inspect Wiring and Connectors | Inspect the wiring and connectors leading to the ECM/PCM power relay for signs of damage, corrosion, or loose connections that could cause excessive voltage. | Flashlight, Multimeter |
| Test the Power Relay | Test the ECM/PCM power relay to ensure it is functioning correctly. Replace the relay if it is faulty and causing the high voltage condition. | Diagnostic Tool, Multimeter |
| Replace the Relay if Necessary | If the power relay is found to be malfunctioning and causing high voltage, replace it to restore proper control module operation. | Replacement Relay, Tools |
| Clear the Code and Test | After repairs, clear the code using an OBD-II scanner and test the vehicle to ensure the ECM/PCM power relay control circuit is functioning correctly. | 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