What it means
Same as P23C7 with the control line shorted to supply. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The fuel heater control module's power-control line carries the command that enables fuel heating on equipped diesel vehicles. This code sets when that line is above its expected electrical level, often because it is shorted to a supply voltage.
Common causes
Most likely first.
- Control line shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light
- Fuel or powertrain warning light, if equipped
- Hard starting or rough running in cold weather
- Reduced engine performance in cold conditions
How to diagnose it
- Check freeze-frame data and related codes to establish when the high control-line reading occurred and whether the fuel heater was commanded on.
- Inspect the fuel heater control module connector and harness for pinched wiring, insulation damage, corrosion, or terminals pushed back.
- Move the control harness carefully while monitoring the circuit reading to check whether the high signal changes with harness position.
- Measure the control line, module supply, and ground against the manufacturer's specification to verify that the control line is high.
- With power isolated as specified by the manufacturer, test the control wire for a short to supply and check connector pin contact.
- If wiring and connector checks pass, test the fuel heater control module's control input and output according to the manufacturer's procedure.
Common fixes
- Repair control wiring that is pinched or shorted to a supply wire.
- Repair damaged insulation where the control line contacts a power source.
- Restore proper contact or replace damaged terminals at the fuel heater control module connector.
- Replace the fuel heater control module if testing confirms its circuit is faulty despite sound wiring.
Can I keep driving?
The vehicle may be drivable in mild conditions if it runs normally, but cold starts can become difficult or rough if fuel heating is affected. Limit use in very cold weather until the high control-line fault is fixed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.