Powertrain, generic · Computer and auxiliary outputs

P0688 ECM/PCM Power Relay Sense Circuit/Open

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

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.

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

Symptoms

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

Repair estimate

DifficultyMediumDIY possible

Parts and labour€10–350

Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

ecm power relayrelay control circuitengine control module

Related codes

P0689 P0690 P0685 P0687 P0562

References: law.cornell.edu, static.nhtsa.gov.