P0687: ECM/PCM Power Relay Control Circuit High

The engine module switches its main relay coil to ground (control circuit), reads the switched voltage back on a sense line and keeps the relay on briefly after ignition off to save learned values. P0687 means the control line is shorted to voltage: when the driver switches on and should pull it to ground, it stays high (0.5 Ω or less to positive) or the driver goes into overcurrent protection, so the relay does not pull in – no supply to the loads, no start or stalling. GM checks with run/crank voltage above 11 V and sets the code after 8 of 10 samples at 250 ms, with the lamp after two trips. The former obdex title (a sense-circuit wording) was a shifted entry; P0687 is the 'high' code of the control circuit. A high voltage on the sense line is P0690.

Medium severity. Can I keep driving?It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

Symptoms

Check engine light
Engine does not start or stalls
Relay does not click

Most likely causes

Control wire shorted to positive (harness, external voltage)
Relay coil shorted (very low resistance)
Module driver faulty

What to check, in order

Start with the simplest. You can tick off each step.

Check the battery and grounds
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Clear the code and see if it returns
If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
Check whether a software update is available
Do not replace the control module without a full diagnosis

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P0687 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
6: Control modules and outputs
87: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0687?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P0687?

The most common causes are: control wire shorted to positive (harness, external voltage); relay coil shorted (very low resistance); module driver faulty.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.