P0690
ECM/PCM Power Relay Sense Circuit HighP0690 is a generic OBD-II powertrain diagnostic trouble code: ECM/PCM Power Relay Sense Circuit High. It is logged by the engine control unit when the glow monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0690 means
P0690 is set when the ECM/PCM detects that the voltage on its main power relay sense circuit is above the expected threshold. The sense line is a feedback wire that lets the ECM confirm whether the relay controlling its own supply voltage is actually open or closed. A high reading means the ECM sees battery-level voltage on that line even when it has not commanded the relay to close — indicating that the relay contacts are welded shut, the sense wire is shorted to battery voltage, or the relay is being energised by an external source.
Because the main power relay feeds the ECM and other critical control circuits, a relay stuck closed creates a condition where the vehicle's electrical system remains partially energised after the ignition is switched off. This causes a constant battery drain that can lead to a no-start condition, and in some cases the ECM itself may be damaged by sustained uncontrolled voltage. The MIL illuminates and the code is stored; on some platforms a hard fault can prevent the ECM from entering low-power sleep mode.
Diagnosis begins by distinguishing whether the relay is physically welded, the harness has a short to battery, or the ECM's internal sense circuitry has failed. Checking for battery drain after key-off and measuring voltage on the sense wire with the relay disconnected will quickly narrow down the fault path. Corroded relay sockets and chafed wiring near the fuse box are common culprits.
Common causes
Most-frequently reported root causes when P0690 is logged.
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1
Main power relay contacts welded closed, keeping the sense line at battery voltage permanently.
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2
Sense circuit wire shorted to battery voltage due to chafed or pinched harness.
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3
Faulty relay that activates without an ECM command (e.g. coil or driver failure).
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4
Corroded or contaminated relay socket causing unintended continuity between terminals.
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5
Failed power distribution module or fusible link feeding uncontrolled voltage to the sense line.
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6
ECM internal sense-circuit failure (moisture intrusion or damaged input driver).
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7
Aftermarket accessory wired incorrectly feeding voltage into the relay output circuit.
Symptoms drivers notice
How to diagnose P0690
A typical diagnostic flow when this code is present.
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1
Retrieve all stored codes and record freeze frame data to establish conditions when P0690 was set.
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2
Perform a key-off battery drain test: if current draw remains above normal after 10 minutes, the relay circuit is staying energised.
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3
Disconnect the main power relay and check whether voltage is still present on the sense terminal — if yes, the harness has a direct short to battery.
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4
With the relay disconnected, measure resistance between the sense wire and battery positive to locate any short in the harness.
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5
Inspect the relay socket, connector pins, and nearby harness routing for corrosion, chafing, or heat damage.
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6
If the harness tests clean, substitute a known-good relay and retest; a welded original relay will show continuity between its switch terminals when unpowered.
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7
If the fault persists with a new relay and a sound harness, suspect ECM internal sense-circuit failure and seek manufacturer-specific guidance before replacing the module.
Vehicles where we've handled P0690
Platforms in our catalogue with confirmed P0690 coverage.
Related powertrain codes
Frequently asked questions
Can I drive with a P0690 code?
Short trips are usually possible since the engine will start, but you risk battery drain leading to a no-start, and the relay staying closed may keep circuits energised when they should be off. Have it diagnosed promptly.
Will P0690 clear itself if the relay stops sticking?
If the fault is intermittent and does not recur within the PCM's monitoring window, it can self-clear after a set number of warm-up cycles — but the underlying cause should still be addressed to prevent repeat failures and potential battery damage.
Is P0690 the same as a bad ECM?
Not necessarily. ECM internal failure is one possible cause, but a welded relay or a shorted harness wire is far more common and should be ruled out first before condemning the ECM.
What relay does P0690 specifically refer to?
It refers to the main power relay that supplies operating voltage directly to the ECM/PCM — sometimes called the EFI main relay or PCM power relay — not the fuel pump or starter relay.
Disabling P0690 in software
RaceTune can permanently disable P0690 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P0690 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch MD1CP002 verified 1 software version
- Bosch MD1CS001 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P0690 in your scan?
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