P2688Fuel Supply Heater Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- With P2688 the heater control line reads too low while the driver is off, which points to a grounded wire: the relay would then be energized all the time, and the filter heater runs even in summer and drains the battery after shutdown. GM's 2020 diesel table requires 0.5 ohm or less to ground and counts 10 failures in 20 samples taken every 100 ms; the code is Type C but, unlike its siblings, triggers a service-vehicle-soon message after one trip (the 2018 table matches). In 2014 GM still rated the same fault Type B with MIL. On the 2015 and 2016 Ford 3.2 L Transit diesel the code belonged to the vaporizer glow plug of the exhaust fuel system and was set after 5 s inside a 1.95–2.175 V window; later model years report that as P269D.
- What you may notice
- Service message or MIL, depending on model year
- Battery drained after the vehicle stands
- Fuel heater running constantly
- Likely causes
- LikelyControl wire chafed against the engine or frame and grounded
- PossibleHeater relay coil shorted internally
- RareWater or fuel in the filter-housing connector
- 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: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.