P2501
Generator Lamp/L-Terminal Circuit High
- Severity
- Medium
- Driving
- Drivable — book it in
The generator lamp or L-terminal circuit is reading high - typically shorted to voltage or a lost earth. Because this circuit both drives the warning lamp and, on many alternators, provides the initial excitation, the practical effect ranges from a lamp that behaves wrongly to no charging at all.
Possible causes
- CommonWiring shorted to voltage or a lost earth on the L terminal circuit
- CommonFailed alternator regulator
- CommonBlown warning lamp bulb
- PossibleCorroded connector at the alternator
- PossibleFailed instrument cluster lamp driver
What you might notice
- Battery warning light stuck on or never lighting
- No charging, or charging only at higher engine speeds
- Battery going flat
- Check engine light on
What to check, in order
- Measure charging voltage at the battery first, so you know whether this is a lamp problem or a charging problem.
- Disconnect at the alternator and see whether the high reading persists at the harness.
- Check the warning lamp bulb and the bulb check at ignition-on.
- Inspect the alternator connector for corrosion and heat damage.
- Check continuity between the alternator and the instrument cluster.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Vehicle speed control, idle control and auxiliary inputs
P2500P2501P2502P2503P2504P2505P2506P2507P2508P2509P2510P2511P2512P2513P2514P2515P2516P2517P2518P2519P2520P2521P2522P2523P2524P2525P2526P2527P2528P2529P2530P2531P2532P2533P2534P2535P2536P2537P2538P2539P2540P2541P2542P2543P2544P2545P2546P2547P2548P2549P2550P2551P2552P2553P2554P2555P2556P2557P2558P2559P2560P2561P2562P2563P2564P2565P2566P2567P2568P2569P2570P2571P2572P2573P2574P2575P2576P2577