Philip54

We replaced the failed alternator of my CIVIC SI with an aftermarket alternator. The new alternator worked fine except that the battery light did not not go off. We tried another alternator (aftermarket,same brand and model) and again we got about 14 volts, but the battery light stays on. What could be the cause of the problem?
Thanks

ezone

That 4 wire connector on the alternator...unplug it and see if the red battery light goes out.

Philip54

Thanks for your reply.

Access to that connector is not possible without opening up the front of the car again. Before I do it could you please provide additional information on why the connector should be unplugged? It would appear to me that the connector is the only connection between the alternator and the car electric system. So if it is unplugged, the alternator does not charge the battery.

Thanks

Colin42

the fat wire held on with a 10mm nut is the positive output of the alternator, the 4 pin connector is what the ecu uses to control the alternator output. If the light goes out when you unplug that 4 pin connector then that shows that the alternator is no good.

Philip54

Thanks. Could you please advise if there is any risk of damaging anything in running the engine with the alternator not controlled by the ECU? I assume that there is not, since you are recommending doing it, but perhaps that is acceptable only for a short time.

CraigW

iTrader: (1)

A short time is all that is needed for testing.

ezone

Zero risk of hurting anything other than your fingers. Alternator is completely disabled while unplugged.



Unplugging it is (usually) a simple and quick diagnostic step.
Just follow instruction and post the result (observation).

Philip54

Thanks

Philip54

Eventually I had to take the car to the Honda dealer. The under dash fuse box and the detector unit in the under hood fuse box were replaced. The lights on the dash are off now.