OBD2 codes.

Generator Lamp/L 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 L circuit, the one that switches on the alternator's regulator (and on some cars the charging light).

What the car has detected

The engine computer doesn't see the expected voltage on the L circuit: for example, low voltage for several seconds with the engine running, or an open circuit.

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

• L 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 L 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.

Original sources · Date indicated: 2026-10-12