Cause
Blown warning lamp bulb
On many alternators the warning lamp circuit is also what starts the alternator charging — the excitation current comes from the battery through the bulb. So a blown bulb can stop the alternator charging entirely, and a flat battery with a lamp that never illuminates is one fault rather than two.
An LED fitted in place of that bulb can break charging the same way, by passing too little current.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (7)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0624 Fuel Cap Lamp Control Circuit Likely for this code Low
- P0648 Immobiliser Lamp Control Circuit Likely for this code Low
- P0649 Speed Control Lamp Control Circuit Likely for this code Low
- P0650 Malfunction Indicator Lamp Control Circuit/Open Likely for this code Moderate
- P0655 Engine Hot Lamp Output Control Circuit Likely for this code Moderate
- P2500 Generator Lamp L-Terminal Circuit Low Likely for this code High
- P2501 Generator Lamp L-Terminal Circuit High Likely for this code High
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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