P0690 ECM/PCM Power Relay Sense Circuit High

The P0690 – ECM/PCM Power Relay Sense Circuit High diagnostic trouble code (DTC) indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected higher-than-expected voltage in the power relay sense circuit.

The ECM/PCM power relay supplies electrical power to the engine and powertrain control system. The control module also monitors the relay circuit to confirm that the expected voltage is present.

When the voltage detected in the relay's monitoring or sense circuit is higher than the programmed limit, the module can store P0690.

What Does P0690 Mean?

In simple terms:

The ECM/PCM is detecting too much voltage on its power-relay sense circuit.

A simplified system can be represented as:

Battery → Fuse → ECM/PCM Power Relay → ECM/PCM

The control module monitors the relay circuit.

If the voltage on the monitored circuit does not behave as expected, the ECM/PCM can set a fault code.

With P0690, the detected voltage is specifically higher than expected.

What Is the ECM/PCM Power Relay?

The ECM/PCM power relay is an electrically controlled switch that supplies power to the engine or powertrain control module and, depending on the vehicle, other related components.

It allows the vehicle to switch high-current electrical circuits using a relatively small control signal.

The relay may supply power to:

• ECM/PCM

• Sensors

• Fuel injectors

• Ignition components

• Solenoids

• Emission-control components

• Other engine-management circuits

The exact circuits controlled by the relay vary by vehicle.

What Is the Relay Sense Circuit?

The sense circuit allows the ECM/PCM to monitor what is happening on the relay's power side.

The module can compare the expected voltage with the voltage it actually detects.

For example:

Relay commanded ON → Expected voltage detected

If the module sees an abnormal voltage instead, it can set a diagnostic code.

With P0690, the voltage is detected as too high.

What Causes P0690?

Possible causes include:

• Short to battery voltage

• Faulty ECM/PCM power relay

• Incorrect relay

• Damaged relay wiring

• Incorrect wiring repair

• Faulty relay socket

• Corroded connector

• Poor electrical connection

• Charging-system overvoltage

• Internal ECM/PCM problem

• Aftermarket electrical modification

The exact cause depends on the vehicle's circuit design.

Can a Bad Relay Cause P0690?

Yes.

A defective relay can cause abnormal voltage behavior.

Possible relay problems include:

• Internal contact failure

• Incorrect switching

• Stuck contacts

• Internal electrical damage

• Incorrect relay installed in the socket

The relay should be tested against the manufacturer's specifications.

Can a Short to Battery Cause P0690?

Yes.

A relay sense wire that becomes connected to battery voltage can cause the ECM/PCM to detect a voltage higher than expected.

Possible sources include:

• Chafed wiring

• Melted insulation

• Pinched harness

• Incorrect previous repair

• Aftermarket electrical equipment

This is an important area to inspect.

Can an Incorrect Relay Cause P0690?

Yes.

Relays that physically fit the same socket do not necessarily have the same electrical configuration.

Installing the wrong relay can change:

• Contact behavior

• Coil operation

• Output voltage

• Control logic

Always verify the relay part number and pin configuration.

Can a Bad Alternator Cause P0690?

Yes, potentially.

If the charging system produces excessive voltage, the ECM/PCM may see higher-than-normal voltage on circuits that should remain within a specific range.

Check for:

• Alternator overcharging

• Voltage regulator failure

• Poor battery connection

• Ground problems

If system voltage is excessively high, the charging system should be repaired before diagnosing the ECM/PCM.

Can a Bad Battery Cause P0690?

A weak battery is more commonly associated with low-voltage problems rather than a high relay-sense voltage condition.

However, a damaged battery or unstable electrical system can contribute to abnormal voltage behavior.

The battery and charging system should still be checked.

Can a Bad Ground Cause P0690?

Potentially.

A poor ground can change the voltage reference used by the ECM/PCM and cause unusual electrical readings.

Inspect:

• Battery negative connection

• Engine ground strap

• Chassis grounds

• ECM/PCM ground connections

A voltage-drop test is preferable to relying only on continuity.

Can the ECM/PCM Cause P0690?

Yes.

The ECM/PCM itself monitors the relay sense circuit.

An internal circuit or input-driver failure can potentially cause an incorrect voltage reading.

However, the ECM/PCM should be considered only after external causes have been eliminated.

Symptoms of P0690

Possible symptoms include:

Check Engine Light

The MIL may illuminate.

Starting problems

If the ECM/PCM does not receive stable power, the engine may be difficult or impossible to start.

Engine stalling

An interruption in ECM power can cause the engine to shut down.

No-start condition

A severe relay or power-supply fault can prevent the ECM from operating.

Intermittent electrical problems

The vehicle may start and run normally at one moment and fail at another.

Transmission problems

If the PCM controls the transmission, an electrical power problem can affect shifting.

Multiple warning lights

Several systems may report faults if communication with the ECM/PCM is interrupted.

Can P0690 Cause a No-Start Condition?

Yes.

The ECM/PCM requires stable electrical power to control the engine.

If the power relay circuit is malfunctioning, the control module may not operate correctly.

A possible sequence is:

Relay problem → ECM/PCM power problem → No engine control → No-start

However, P0690 itself does not prove that the ECM has lost power completely.

Can P0690 Cause Stalling?

Yes, potentially.

If power to the ECM/PCM is interrupted while driving, the engine can stall.

An intermittent relay, poor connection, or damaged power circuit can cause intermittent stalling.

Can P0690 Cause Limp Mode?

Potentially.

If the PCM detects an electrical problem affecting critical control circuits, it may enter a fail-safe operating mode.

The exact response depends on the manufacturer.

Can P0690 Cause Transmission Problems?

Yes.

On vehicles where the PCM also controls transmission functions, an unstable PCM power supply can affect:

• Gear shifting

• Solenoid operation

• Torque-converter control

• Transmission communication

Transmission-related DTCs may also be stored.

How Is P0690 Diagnosed?

A systematic electrical diagnosis is important.

1. Scan all control modules

Record all:

• Stored DTCs

• Pending DTCs

• Communication codes

• Voltage-related codes

Other codes can help identify the source.

2. Check battery voltage

Verify battery condition and voltage.

3. Check charging voltage

Make sure the alternator is not producing excessive voltage.

4. Identify the ECM/PCM power relay

Use the vehicle-specific fuse and relay diagram.

5. Inspect the relay

Check for:

• Burn marks

• Melted plastic

• Corrosion

• Incorrect relay

• Loose terminals

6. Test the relay

Check the coil and switching contacts according to manufacturer specifications.

7. Measure the relay sense voltage

Compare the actual voltage with the specified value.

8. Check for battery voltage on the sense wire

Determine whether the sense circuit is receiving unwanted voltage.

9. Inspect the harness

Look for:

• Chafing

• Pinching

• Melted wiring

• Poor repairs

• Aftermarket connections

10. Check ECM/PCM grounds

Perform voltage-drop testing where appropriate.

11. Check the relay socket

A damaged terminal inside the fuse box can create an abnormal electrical condition.

12. Evaluate the ECM/PCM

Only after the external circuit has been verified should internal module failure be considered.

Can a Multimeter Diagnose P0690?

Yes.

A multimeter can be used to measure:

• Battery voltage

• Charging voltage

• Relay coil resistance

• Relay output voltage

• Sense-circuit voltage

• Voltage drop

• Continuity

• Short circuits

The readings should always be compared with the manufacturer's specifications.

Can a Scan Tool Help?

Yes.

A scan tool can provide useful information such as:

• ECM/PCM communication status

• System voltage

• Stored and pending DTCs

• Freeze-frame data

If the vehicle intermittently loses communication with the ECM, that can be an important clue toward a power-supply problem.

What If P0690 Appears With Many U-Codes?

This is an important diagnostic clue.

If several modules suddenly report communication errors, do not immediately assume that multiple modules have failed.

A common power problem can produce:

ECM/PCM power problem → Network communication interruption → Multiple U-codes

Check the ECM/PCM power supply, grounds, battery, and relay circuit first.

What If P0690 Appears After Battery Replacement?

Check:

• Battery terminals

• Battery polarity

• Ground connections

• Fuse box connections

• ECM/PCM power relay

• System voltage

If the problem appeared immediately after battery service, inspect the electrical connections that were disturbed.

What If P0690 Appears After Jump-Starting?

This is worth investigating carefully.

A jump-start event can involve:

• Voltage fluctuations

• Incorrect connection

• Electrical surges

• Weak battery conditions

Check the battery, charging system, relay circuit, and module power supply.

What If P0690 Appears After Electrical Modification?

Inspect any recently installed equipment, such as:

• Remote starters

• Alarms

• Audio systems

• Tracking devices

• Additional lighting

• Other aftermarket electronics

Poorly installed accessories can interfere with ECM/PCM power circuits.

Is P0690 a Serious Code?

It can be serious.

The ECM/PCM is one of the most important control units in the vehicle.

A power-relay problem can result in:

• No-start

• Stalling

• Reduced engine performance

• Transmission problems

• Intermittent electrical failures

If the vehicle is stalling or losing power unexpectedly, the problem should be diagnosed promptly.

Can You Drive With P0690?

If the vehicle runs normally and the code is stored without symptoms, a short trip to a repair facility may be possible.

However, driving is not recommended if you experience:

• Engine stalling

• No-start conditions

• Sudden loss of power

• Multiple electrical warning lights

• Repeated ECM communication loss

An intermittent power-supply problem can cause the engine to shut down unexpectedly.

How Is P0690 Repaired?

The repair depends on the confirmed cause.

Possible repairs include:

• Replacing the ECM/PCM power relay

• Correcting an incorrect relay

• Repairing a shorted sense wire

• Repairing damaged wiring

• Repairing relay-socket terminals

• Cleaning or replacing corroded connectors

• Repairing ECM/PCM power or ground circuits

• Repairing charging-system overvoltage

• Removing an incorrect aftermarket electrical connection

• Repairing or replacing the ECM/PCM when an internal failure is confirmed

Does P0690 Require Relay Replacement?

Not automatically.

The relay is a possible cause, but the control and sense circuits should also be tested.

A short to battery voltage can produce the same code even when the relay itself is functioning correctly.

Does P0690 Require ECM Replacement?

Usually not.

The ECM should be the last major component considered after verifying:

Battery → Alternator → Fuses → Relay → Relay socket → Sense circuit → Wiring → Grounds → ECM

Replacing the ECM without finding an external electrical fault can result in unnecessary expense.

Common Diagnostic Mistakes

Replacing the ECM immediately

The fault is often related to the relay or wiring.

Replacing the relay without testing the circuit

A shorted sense wire can cause the replacement relay to produce the same code.

Ignoring charging voltage

An overcharging alternator can create high-voltage electrical faults.

Ignoring grounds

Poor grounds can create misleading voltage readings.

Installing a relay based only on physical fit

The relay must have the correct electrical configuration.

Ignoring aftermarket accessories

Incorrect electrical modifications can interfere with the ECM power supply.

P0685 vs. P0689 vs. P0690

These codes all relate to ECM/PCM power-relay circuits but describe different conditions.

P0685 – ECM/PCM Power Relay Control Circuit/Open

Indicates a general open or control-circuit problem.

P0689 – ECM/PCM Power Relay Sense Circuit Low

Indicates that the monitored relay-sense voltage is lower than expected.

P0690 – ECM/PCM Power Relay Sense Circuit High

Indicates that the monitored relay-sense voltage is higher than expected.

The key difference is:

P0689 → Sense circuit voltage too low

P0690 → Sense circuit voltage too high

How Do You Clear P0690?

The correct procedure is:

Scan all modules → Record all DTCs → Check battery → Check charging system → Identify ECM/PCM relay → Inspect relay and socket → Measure sense voltage → Check for short to battery → Inspect wiring → Check grounds → Verify ECM/PCM operation → Repair the confirmed fault → Clear codes → Start vehicle → Road test → Rescan

If P0690 returns, the high-voltage condition in the ECM/PCM power-relay sense circuit has not been resolved.

Final Thoughts on P0690

P0690 – ECM/PCM Power Relay Sense Circuit High indicates that the ECM or PCM has detected higher-than-expected voltage in the circuit it uses to monitor its power relay.

Possible causes include a faulty relay, incorrect relay, short to battery voltage, damaged wiring, relay-socket problem, charging-system overvoltage, poor electrical connections, or, less commonly, an internal ECM/PCM fault.

The most important point is that P0690 does not automatically mean the ECM/PCM is defective.

A proper diagnostic sequence is:

Check battery → Check alternator → Inspect relay → Test relay socket → Measure sense circuit → Check for unwanted battery voltage → Inspect wiring → Check grounds → Evaluate ECM/PCM.

If the vehicle has starting problems, intermittent stalling, or sudden loss of engine power, the fault should be addressed promptly because an ECM/PCM power-supply problem can potentially cause the engine to shut down unexpectedly.