P0687

ECM/PCM Power Relay Sense Circuit Open

ECM/PCM Power Relay Sense Circuit Open: the circuit is open. Likely a broken wire, disconnected connector, or failed component.

Check engine light: Yes
Emissions related: Yes
Repair difficulty: medium

Symptoms

Check engine light on
Possible limp mode or no-start
Multiple follow-up faults across modules
Reset/relearn may be needed after repair

Common causes

Ordered by how often each turns out to be the cause.

Main relay contacts faultyCommon
Sense wire openPossible
Pin pushed back out of connector bodyLess likely

Parts involved

ECM
Main Relay

P0687 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.