P0688ECM/PCM Power Relay Sense Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine light
- Engine cranks but intermittently does not start (Stellantis)
- Engine stalls while driving
- Likely causes
- LikelyTerminal in the sense or ASD circuit connector bent, pushed back or spread
- PossibleBlown fuse in the monitored load circuit (e.g. shorted ignition coil)
- PossibleRelay contact does not close
- RareModule input faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €10 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.