EN

Severity: Low Code type: Generic (all makes)

P0690 Code: ECM/PCM Power Relay Sense Circuit High

The ECM still sees power coming through its main relay when the relay should be off – often stuck contacts.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
ECM/PCM Power Relay Sense Circuit High
System
ECU & Outputs · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$0–$1,800
DIY difficulty
Easy

Besides switching its main power relay, the ECM reads back the relay's output through a sense circuit to confirm the relay really did what it was told. P0690 means that sense line showed voltage at a moment when the relay was supposed to be open. Many ECMs make this check at key-on, just before energizing the relay, and again at the end of the after-run once the key is off. The classic cause is a relay whose contacts have welded or stuck closed, often because a shorted load downstream pulled a heavy current through them. A sense wire touching a live circuit, or aftermarket equipment tapped into a fuse on the relay's output, can back-feed the same voltage. The engine usually runs normally, but with the relay stuck on, the ECM and its loads may stay powered after shutdown.

Can I keep driving? The car is normally fine to drive. Keep an eye on the battery: if it's weak after the car sits, pull the main relay or disconnect the battery when parking until it's fixed.

How to read P0690

How to read P0690P10263904
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 6 Computer & outputs
  4. 90 Specific fault

Symptoms

  • Check engine light, often with no drivability change
  • Code sets right at key-on or shortly after the engine is switched off
  • Main relay stays clicked in after the after-run should have ended
  • Battery weak after the car sits for a day or two
  • Idle quality or throttle adaptations lost after each restart because the after-run never completes properly

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Main relay contacts welded or sticking closed 34%
  2. Sense wire shorted to a battery-powered circuit 18%
  3. Aftermarket device, such as a dash-cam hardwire kit, tapped into a fuse fed by the relay and back-feeding it 14%
  4. Shorted load on the relay's output that welded the contacts 14%
  5. Wrong relay type fitted, such as a changeover relay wired incorrectly 10%
  6. Faulty sense input in the ECM 10%

Diagnosis step by step

Diagnostic flow: P06901Find out when the code sets2Measure the relay output with thekey off3Pull the relay and measure again4Hunt for back-feed if voltageremains5Check the loads that welded thecontacts6Verify over several key cycles

  1. Find out when the code sets

    Check freeze frame data and clear the code, then cycle the key on and off a few times while watching for it to return. A code that comes back at key-on means the ECM found power on the sense line before it even energized the relay.

    Tools: OBD-II scanner

  2. Measure the relay output with the key off

    Wait until the after-run is over, then measure the relay's output terminal and the ECM sense pin. Both should read 0 V. Battery voltage on either one confirms what the ECM is reporting.

    Tools: Multimeter

  3. Pull the relay and measure again

    Remove the relay and check the output terminal in the socket. If the voltage vanishes, the relay is stuck: on the bench, the switched contacts must read open with the coil unpowered. Tapping a stuck relay sometimes frees it briefly, but it should be replaced.

    Tools: Multimeter, Pliers

  4. Hunt for back-feed if voltage remains

    With the relay out and voltage still present, something else is powering that line. Remove fuses on the relay's output side one by one, and look for add-on wiring such as fuse taps for dash cams, lighting or trackers. Those often connect to an ECM or injector fuse and feed voltage backward.

    Tools: Multimeter, Flashlight

  5. Check the loads that welded the contacts

    If the relay was stuck, find out why. Measure the resistance of the injectors, coils and sensor heaters it feeds, and check whether a fuse on its output was upgraded. A shorted load will weld a new relay the same way.

    Tools: Multimeter

  6. Verify over several key cycles

    Fit the correct relay, clear codes and do several key-on, key-off cycles, listening for the relay to release after the after-run. The code should not return, and the battery should hold charge overnight.

    Tools: OBD-II scanner

Where the parts are

Charging system and control modules – P06901234567
Charging system and control modules
  1. 1Battery
  2. 2Alternator
  3. 3Engine computer (ECM)
  4. 4CAN bus
  5. 5Transmission
  6. 6Wheel speed sensor
  7. 7High-voltage battery

Repair options & costs

RepairDIY?Estimated cost
Replace stuck main relay Yes $25–$120
Remove aftermarket fuse tap and rewire correctly Yes $0–$150
Repair sense wire shorted to power No $120–$380
Replace shorted injector, coil or heater circuit component No $100–$450
Repair or replace ECM No $300–$1,800

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Depends

Not every vehicle turns on the check engine light for P0690. If it's on, the car fails an OBD emissions test; if a stuck relay has been draining the battery, readiness monitors may also be reset and need several drive cycles.

Frequently asked questions

Is P0690 serious?

Usually not for driving – the engine runs normally. The real risks are a battery that goes flat because the ECM and its loads stay powered, and a relay that could also fail open later and stop the engine.

I just installed a dash cam. Could that cause P0690?

Yes, if its hardwire kit was tapped into a fuse on the ECM or injector circuit. With the key off, the dash cam's own supply can back-feed voltage into the relay's output, and the ECM reads that as a stuck relay. Move the tap to a proper accessory circuit.

Why do relays weld shut?

A heavy current surge across the contacts, such as from a shorted injector, coil or fan motor, can melt the contact surfaces together. Replacing the relay without finding that load often means the new one welds too.

What's the difference between P0690 and P0687?

P0690 is about the relay's output side, which the ECM monitors to confirm the contacts opened. P0687 is about the control wire the ECM uses to energize the coil. Stuck contacts point to P0690; a live control wire points to P0687.

Sources