ECM/PCM Power Relay Sense Circuit Intermittent

Possible causes

• CommonFailed power relay with worn or sticking contacts
• CommonCorroded relay socket or fuse box connections
• CommonWater ingress into the fuse box
• PossibleWiring fault on the sense circuit
• PossibleWeak battery making relay operation marginal
• RareFailed module input

What you might notice

• Occasional limp mode that clears after a restart
• Engine occasionally dead at start-up
• Fault linked to wet weather
• Check engine light coming and going

What to check, in order

1. Note whether it happens in the wet. Water in the fuse box is a very common cause of intermittent relay faults and is easily missed.
2. Swap the relay with an identical one from elsewhere in the box and see whether the fault follows it. It costs nothing and is the fastest test available.
3. Inspect the relay socket for corrosion and heat damage - a discoloured socket means the relay has been running hot.
4. Check the fuse box for water ingress, particularly if it is mounted low or in the engine bay.
5. Check battery voltage - a weak battery makes a marginal relay behave like a failing one.
6. If the battery goes flat overnight, investigate this rather than replacing the battery. A relay that will not release keeps the module powered all night.