What it means
Same as P23C7 with the control line shorted to ground. 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 the line is below its expected electrical level, typically because it is shorted to ground or has a poor, high-resistance connection.
Common causes
Most likely first.
- Control line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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
- Review freeze-frame data and related codes to determine whether the low control-line reading occurred during a cold start or heater command.
- Inspect the fuel heater control module connector and control harness for chafing, moisture, corrosion, and loose or pushed-back pins.
- With the code active, move the control harness carefully while monitoring the circuit reading to check for an intermittent short or connection fault.
- Measure the control line and module power and ground against the manufacturer's specification to confirm the low circuit condition.
- With power isolated as specified by the manufacturer, check the control wire for a short to ground and verify terminal contact.
- If the control wiring and connectors pass, test the fuel heater control module's input and output using the manufacturer's procedure.
Common fixes
- Repair control wiring that is chafed and shorted to ground.
- Clean or replace corroded terminals and restore proper connector pin fit.
- Repair a poor module power or ground connection if testing identifies it.
- Replace the fuel heater control module if its circuit remains low with sound wiring and connections.
Can I keep driving?
In mild weather, driving is usually possible if the engine runs normally, but cold starting may become difficult or rough without fuel heating. Avoid depending on the vehicle in very cold conditions until the circuit is repaired.
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.