What Does P0689 Mean?
The PCM has detected a low voltage condition on the ECM/PCM power relay sense circuit. The sense circuit is reading lower voltage than expected, indicating the relay contacts may be degraded, there is excessive resistance in the power feed, or the sense wire has a short to ground. The PCM may incorrectly believe it is losing power, leading to erratic engine behavior.
Safety Warning
Low sense voltage may cause the PCM to enter a degraded operating mode or shut down unexpectedly. This can result in a stall while driving. Repair promptly, especially if intermittent stalling or no-start symptoms are occurring.
Common Causes
30%
Degraded relay contacts causing voltage drop (arcing/pitting)
25%
Short to ground in the sense circuit wiring
20%
Excessive resistance in power feed to the relay (corroded terminals)
15%
Low system voltage due to weak battery or charging system fault
10%
Corroded PCM connector pin at the sense circuit input
Diagnostic Steps
1
Measure battery voltage at the battery terminals with the engine running; it should be 13.5-14.5V. Low charging voltage can cause this code.
2
With the relay engaged, measure voltage at the relay sense output pin and at the PCM sense input pin; compare the two. More than 0.5V difference indicates resistance in the sense wire.
3
Perform a voltage drop test across the relay contacts while the PCM is powered; more than 0.2V drop indicates worn/pitted contacts requiring relay replacement.
4
Check the sense wire for shorts to ground by disconnecting both ends and measuring resistance to chassis ground; it should read OL.
5
Inspect the fuse box power feed terminals for corrosion or heat damage that could reduce the voltage available to the relay and sense circuit.
Estimated Repair Cost
$50 - $500
Parts + labor, varies by vehicle and location
The PCM has detected a low voltage condition on the ECM/PCM power relay sense circuit. The sense circuit is reading lower voltage than expected, indicating the relay contacts may be degraded, there is excessive resistance in the power feed, or the sense wire has a short to ground. The PCM may incorr...
The most common cause of P0689 (ECM/PCM Power Relay Sense Circuit Low) is: Degraded relay contacts causing voltage drop (arcing/pitting)
Typical repair costs for P0689 range from $50 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Low sense voltage may cause the PCM to enter a degraded operating mode or shut down unexpectedly. This can result in a stall while driving. Repair promptly, especially if intermittent stalling or no-start symptoms are occurring.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0689 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Control Module Power Supply
Difficulty
Type
Generic (SAE)
Recommended Tools
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