P0688 on 2006-2018 RAM 2500 (2500) — ECM/PCM Power Relay Sense Circuit/Open
1 vehicles · 1 makes · $300-$1,200 repair
Most Reported On
P0688 is an OBD-II diagnostic trouble code meaning “ECM/PCM Power Relay Sense Circuit/Open.” An open or general fault in the sense (feedback) circuit the module uses to verify the ECM/PCM power relay output. The module cannot confirm relay power is present. This code is most commonly reported on 2006-2018 RAM 2500 (2500), with repair costs ranging from $300 to $1,200.
Common Causes
Typical Repair Cost
Based on 1 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
This is a powertrain code, so a basic OBD-II reader can read it. These read P0688.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple code reader for engine (P) codes on many compatible OBD-II vehicles. It does not support every vehicle or hybrid/EV application, and it does NOT read body, chassis or network codes; confirm exact-vehicle compatibility before buying.
- Read & clear engine (P) codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth scanner with a companion app that reads beyond the engine module — ABS, SRS and transmission — plus manufacturer-specific codes on many vehicles.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X V3.0 Elite OBD-II Scanner
by LAUNCH
Handheld scanner covering the four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level tablet with all-system coverage and bi-directional control, so you can command a module rather than only read it.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
What you can do yourself, and what needs a shop
Reading the code, clearing it, and watching whether it returns is a driveway job with the right scanner. These steps are not:
- Module programming or software updates — needs the manufacturer software or a J2534 pass-through with a paid subscription.
- Replacing a control module — most are VIN-programmed and immobilizer-registered, so a new one does nothing until it is coded to your car.
- Airbag/SRS component work — a stored fault can deploy a live device.
If the vehicle is still under warranty, check for an open recall or technical service bulletin before buying anything — the repair may already be covered.
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FAQ
What does P0688 mean?
P0688 stands for "ECM/PCM Power Relay Sense Circuit/Open." An open or general fault in the sense (feedback) circuit the module uses to verify the ECM/PCM power relay output. The module cannot confirm relay power is present.
What are the most common causes of P0688?
The most common causes of P0688 are: Open in the power relay sense circuit, Faulty ECM/PCM power relay, Corroded/damaged connectors, Blown fuse on the sensed feed, Internal PCM fault. The specific cause varies by vehicle.
How much does it cost to fix P0688?
Repair costs for P0688 range from $300 to $1,200, depending on the vehicle and root cause.
Which vehicles are affected by P0688?
Au7o has documented P0688 across 1 vehicle models from 1 manufacturers: RAM.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.