What it means
The fuel supply heater does not raise fuel temperature within the calibrated time window. Common in diesel and biofuel installations to prevent paraffin or fat crystallisation in cold weather.
At a glance
- Usually lights the check-engine light
How it works
The fuel supply heater warms fuel in vehicles equipped with a system designed to reduce cold-weather thickening or crystallisation. The control module sets this code when monitored fuel temperature does not rise as expected within the calibrated time, which can indicate weak heater output or low supply voltage under load.
Common causes
Most likely first.
- Heater element aged - low output
- Supply voltage low under load
Symptoms
- Check-engine light
- Hard starting in cold weather
- Rough running until warm
How to diagnose it
- Record freeze-frame data and check ambient and fuel temperature readings to confirm the fault occurred during conditions when the heater should operate.
- Inspect the heater connector, fuse, wiring, and ground for corrosion, looseness, or heat damage.
- Check charging and supply voltage while the heater is commanded on, following the vehicle wiring diagram and manufacturer's specification.
- Measure heater current or element resistance using the manufacturer's procedure to determine whether the element is producing expected output.
- If electrical supply and heater operation check out, verify that the fuel temperature sensor reading is plausible and that fuel is flowing as designed.
Common fixes
- Repair a loose, corroded, or damaged heater connector or ground.
- Repair a fuse, wiring, or supply-voltage fault affecting the heater under load.
- Replace the fuel supply heater element if its output is below specification.
- Repair or replace a faulty fuel temperature sensor if its reading prevents correct heater monitoring.
Can I keep driving?
In cold weather, starting may become difficult and the engine may run roughly until it warms; avoid repeated extended cranking. If the vehicle starts and runs normally, a short trip may be possible, but cold conditions can leave it unable to start.
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.