P0688 code meaning
ECM/PCM Power Relay Sense Circuit/Open
Powertrain system Generic code P06xx codes Check engine light
What P0688 means
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.
P0688 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0688
- Check engine light
- Engine cranks but intermittently does not start (Stellantis)
- Engine stalls while driving
Common causes of P0688
- Most 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
- Less likelyModule input faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
ECM power relayRelay control circuitEngine control module
What each part of P0688 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 88 | The exact fault in that area. |
What to do next
- Note P0688 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0688
What does P0688 mean?
P0688 means "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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0688?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0688 fail an emissions test?
Yes, it can. P0688 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0688 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0688 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.