P0688 — ASD / ECM-PCM Power Relay Sense Circuit Open
CAUTIONIs it safe to drive? Drive gently and get it looked at soon — it can worsen or fail inspection.
What P0688 means
This is a manufacturer-specific code — its meaning depends on the vehicle’s make (see below).
What P0688 means on specific makes
Dodge / Jeep / Ram / Chrysler CAUTION
Generic SAE code but very high-frequency on Chrysler/Dodge/Ram. The PCM monitors the Auto-Shutdown (ASD) relay output voltage through a sense wire; if it sees the circuit open, it sets P0688. A blown fuse (e.g., F63 ignition-coil fuse) or bad ASD relay are common real causes — can cause a no-start.
- Blown fuse feeding ASD output (e.g., F63) ($5-15)
- Failed ASD/PCM power relay ($15-60)
- Corroded/loose wiring at relay or PCM ($0-100)
- PCM internal fault (rare) ($varies)
Check first: Check the ASD-related fuses FIRST (Ram owners report F63), then swap/test the ASD relay; inspect the sense-circuit wiring.
Source: OBD-Codes.com P0688 / RamForum / CarParts.com / KBB