ECM/PCM Power Relay Sense Circuit High
Code P0690 indicates the PCM has detected an abnormally high voltage signal in the ECM/PCM power relay sense circuit. This circuit monitors the relay's switching function, and a high voltage reading suggests a fault in the relay itself, its power supply, or the wiring connecting them.
What You Might Notice
- Engine fails to start or starts with significant delay
- Electrical accessories not functioning properly
- Engine drivability issues or rough running
- Check Engine Light illuminated
- Multiple electrical system malfunctions
Most Common Causes
- 1
Defective PCM Power Relay
The power relay itself has failed internally, preventing proper voltage regulation to the sense circuit. This is the most common cause and requires relay replacement.
- 2
Blown Fuse or Fusible Link
A fuse or fusible link protecting the relay circuit has blown, interrupting power supply and causing the high voltage sense signal. Check the fuse box for blown fuses related to the PCM power supply.
- 3
Open or Shorted Wiring
An open circuit between the relay and PCM or a short to ground/voltage in the sense circuit wire creates abnormal voltage levels. Damaged, corroded, or improperly connected wiring is often responsible.
- 4
PCM Connector Issues
Loose, corroded, or damaged connector pins at the PCM or relay can create poor electrical contact and sense circuit voltage faults. Oxidation and connection problems accumulate over time.
How to Diagnose It
- 1
Check Defective PCM Power Relay — The power relay itself has failed internally, preventing proper voltage regulation to the sense circuit. This is the most common cause and requires relay replacement.
- 2
Check Blown Fuse or Fusible Link — A fuse or fusible link protecting the relay circuit has blown, interrupting power supply and causing the high voltage sense signal. Check the fuse box for blown fuses related to the PCM power supply.
- 3
Check Open or Shorted Wiring — An open circuit between the relay and PCM or a short to ground/voltage in the sense circuit wire creates abnormal voltage levels. Damaged, corroded, or improperly connected wiring is often responsible.
- 4
Check PCM Connector Issues — Loose, corroded, or damaged connector pins at the PCM or relay can create poor electrical contact and sense circuit voltage faults. Oxidation and connection problems accumulate over time.
How to Fix It
- 1
Replace PCM Power Relay
Locate the PCM power relay in the engine bay fuse/relay box using the vehicle service manual. Unplug the old relay and install a new OEM-equivalent relay, ensuring proper seating. Test that the engine starts normally and the code clears.
- 2
Inspect and Replace Blown Fuses
Open the main fuse box and locate the fuse or fusible link protecting the PCM power relay circuit using the fuse diagram. Replace any blown fuses with the correct amperage rating and verify proper operation.
- 3
Test and Repair Wiring
Using a digital multimeter, test the sense circuit wire for continuity and shorts between the relay and PCM connector. Look for damaged insulation, corrosion, or loose connections. Repair or replace damaged wiring segments as needed.
- 4
Clean and Reseat PCM Connectors
Disconnect the PCM and relay connectors and inspect for corrosion or bent pins. Clean connector contacts with electronics-safe cleaner, reseat connections firmly, and ensure proper seating. Clear the code and retest.
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