A 1999 Mitsubishi Magna owner described poor charging at idle with electrical loads switched on. Measurements also differed between a cold engine and normal operating temperature.
The misleading early check
The owner initially thought the alternator diodes tested satisfactorily. That did not explain the charging failure after the vehicle warmed up. The discussion considered alternator condition and other possible causes.
The owner’s follow-up
Raj later reported restoring charging using parts from a second-hand alternator and said the battery warning light no longer appeared. The owner attributed the fault to diodes failing during operation. The thread does not provide an independent component-failure analysis, so that explanation remains an author-reported conclusion.
The practical lesson
Tell the workshop when the warning appears: cold or warm, at idle or higher engine speed, and with which loads. Ask for testing under the failing conditions rather than one unloaded reading. Do not treat voltages from this older vehicle as universal targets for modern managed charging systems. Replacement parts must match the vehicle; this account is not an alternator-rebuilding procedure.
Author follow-up · not independently verified
For information, not a diagnosis or repair instruction. A reported result may not apply to your car. Consult the manufacturer's guidance and a qualified technician.
How to use this information
This is an editorial interpretation of a public discussion. Replies, votes and an accepted answer do not prove a diagnosis. An author-reported finding or repair has not been independently verified by AI4Car. Illustrations are conceptual. Read the content limitations.
Credits & reuse
AI-assisted adaptation by AI4Car of the contributions below on Motor Vehicle Maintenance & Repair Stack Exchange. We shortened and reorganized the discussion, paraphrased its text and added educational context. These are reported experiences, not independently verified repairs. The contributors do not endorse AI4Car.
- Question: Alternator doesn't charge the battery when idle with head lights onBy Raj · CC BY-SA 4.0
- Comment / follow-up: Alternator doesn't charge the battery when idle with head lights onBy Raj · CC BY-SA 4.0
- Comment / follow-up: Alternator doesn't charge the battery when idle with head lights onBy F Dryer · CC BY-SA 4.0
This adapted article text, including AI4Car’s additions, is available under CC BY-SA 4.0. Reuse is permitted under that license with attribution, an indication of changes and ShareAlike. This notice excludes the separate illustration, site design and user comments. The source revision history remains available at Stack Exchange.
Illustration: AI-generated for AI4Car; a generic conceptual view, not a photograph of the reported vehicle or a manufacturer’s diagram. Content and licensing policy.
Was this useful?
Discussion
Share what you checked, what changed, and which vehicle you drive. Up to 10 comments and replies per account in 24 hours.
Loading discussion…