The P0686: ECM/PCM Power Relay Control Circuit Low code indicates that the control module has detected low voltage in the power relay control circuit for the ECM (Engine Control Module) or PCM (Powertrain Control Module). This can lead to issues with starting the vehicle, improper module operation, or engine performance problems. Low voltage in the circuit could be caused by a faulty relay, wiring issues, or a control circuit malfunction.
P0686 – Quick Overview
| Code | Information |
|---|---|
| Meaning | P0686: ECM/PCM Power Relay Control Circuit Low |
| Is it serious? | Yes, as it can affect engine starting and performance. |
| Possible causes | – Low 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 |
P0686 Meaning
The P0686 code means that the ECM or PCM is receiving a lower-than-expected voltage in the power relay control circuit. This relay controls the power supplied to the control modules, and a low voltage can prevent the modules from functioning properly, leading to starting difficulties and other performance issues.
Step-by-step diagnostic guide
| Action | Description | Tools Needed |
|---|---|---|
| Check for Other Codes | Use an OBD-II scanner to check for any other related codes, especially those affecting the ECM or PCM, to gather more context about 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 voltage readings to the manufacturer’s specifications. | Multimeter |
| Inspect Wiring and Connectors | Inspect the wiring and connectors leading to the ECM/PCM power relay for any signs of damage, corrosion, or loose connections that could cause low voltage. | Flashlight, Multimeter |
| Test the Power Relay | Test the ECM/PCM power relay to ensure it is functioning properly. If the relay is faulty, replace it to restore proper operation of the control modules. | Diagnostic Tool, Multimeter |
| Replace the Relay if Necessary | If the power relay is found to be faulty and causing low voltage, replace it to ensure the control modules receive the correct power supply. | 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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