P0688: ECM/PCM Power Relay Sense Circuit/Open

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. P0688 means the expected switched voltage does not arrive on the sense line – the line is open, a fuse in the monitored path has blown or the contact does not close. Chrysler (Stellantis) calls the relay 'auto shutdown (ASD) relay'; a service case for intermittent no-starts with P0688 points first to spread or pushed-back terminals in the ASD circuit connector. GM does not use P0688 and reports an open sense line as P0689. The former obdex title (a duplicate of P0690) was a shifted entry.

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 cranks but intermittently does not start (Stellantis)
Engine stalls while driving

Most likely causes

Terminal in the sense or ASD circuit connector bent, pushed back or spread
Blown fuse in the monitored load circuit (e.g. shorted ignition coil)
Relay contact does not close
Module input faulty

What to check, in order

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

Check the battery and grounds
Check the continuity of the wire between the component and the control module.
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 P0688 means

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

Frequently asked questions

Can I keep driving with code P0688?

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 P0688?

The most common causes are: terminal in the sense or ASD circuit connector bent, pushed back or spread; blown fuse in the monitored load circuit (e.g. shorted ignition coil); relay contact does not close.

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.