What it means
The control line that energises the fuel heater control module - used on diesel systems for cold-weather fuel preheating - is open.
At a glance
- Usually lights the check-engine light
How it works
On a diesel equipped with a fuel heater, the fuel heater control module receives a control signal that enables or manages heating in cold conditions. This code sets when the module's power-control circuit is open, so the heater may not operate when needed.
Common causes
Most likely first.
- Open in control wiring
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
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 fuel-heater or powertrain codes to establish whether the fault occurred during cold conditions.
- Inspect the fuel heater control module connector and control wiring for loose connections, broken conductors, corrosion, or pins pushed back.
- Check the relevant fuse and power and ground feeds using the manufacturer's wiring diagram before testing the control line.
- Measure continuity of the control line between the engine controller and fuel heater control module against the manufacturer's specification.
- Check connector pin contact and module power and ground under the conditions specified by the manufacturer.
- If wiring and connections are intact, test the fuel heater control module and its control output using the manufacturer's procedure.
Common fixes
- Reconnect the fuel heater control module plug or secure a pushed-back terminal.
- Repair an open or broken control wire to the fuel heater control module.
- Repair a poor module power or ground connection if found.
- Replace the fuel heater control module if its wiring and feeds pass but the control circuit remains open.
Can I keep driving?
The vehicle may run normally in mild weather, but cold starts can become difficult or rough if fuel preheating is unavailable. Avoid relying on it in very cold conditions until the fuel-heater circuit is checked.
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.