Generator Field/F Terminal Circuit
The alternator recharges the battery while the engine runs, and the engine computer controls how much it charges through control wires. This code means a fault in the F circuit, through which the engine computer receives how hard the alternator is working (the field signal).
What the car has detected
The F circuit signal doesn't make sense: with the ignition on and engine off it should be near zero, and with the engine running it should vary within a range, and it doesn't.
If the battery light comes on with the engine running, the alternator may not be charging: the car will run on the battery until it is flat and then stop. Go to a garage soon and avoid switching on unnecessary loads.
Symptoms
- Battery light on with the engine running
- Engine warning light on
- Battery running flat
- Lights or accessories failing if the battery gets very low
Possible causes
- F control wire broken, poorly connected or shorted
- Loose or corroded alternator connector
- Failed alternator or voltage regulator
- Control fault in the engine computer (less common)
Checks for the garage
- Check battery voltage and charging voltage with the engine running
- Check the alternator's main supply (B+) and earth
- Check the F control wire between the alternator and the engine computer for breaks or shorts
- Look at the alternator control signal with diagnostics, engine off and running
- Replace the alternator or engine computer only after checking the wiring
Next step
Have the charging voltage, the alternator control wire and its connector checked.
Go to a garage soon, especially if the battery light is on. Charging circuit checks need a multimeter and diagnostics.