1997 Nissan Maxima GLE - replaced alternator

[luedemann]

Alright, so I had the alternator changed in my Maxima. It runs great with no problems so far but the brake and battery light are still on! The mechanic said that it is probably caused by a burnt out diode in the cluster. What do you guys think?

[loystock]

The Battery and Brake light coming on is indicative of problem with the charging system or a partial short somewhere, draining too much current and lowering the alternator output. You may have a new alternator but the output is marginal (I've seen this in refurbished ones).

First, make sure the battery connections are clean and tight - no corrosion. A fully charged battery should read 12.6 or higher with engine off. With the engine running, the alternator charging voltage must be STEADY (no fluctuation) and must be > 13.8 VDC (spec is 14.1-14.7 VDC). Check all the fuses in the engine compartment. Check the wiring, especially on the alternator side as it is possible to have 'crossed wires.' Check the battery cable for corrosion, especially the 'hot' (+) side which can be shorting to ground. Check the wiring under the fusible links/fuses.

Have you done any modification to your headlight (high wattage bulbs)? Are the headlights working good? Check the condition of the wiring to headlights.

[luedemann]

I will definitely check all that tomorrow. Is there a problem with running the car like it is now if it is not the alternator? Does the diode explanation make sense?

[loystock]

Not a good idea to drive the car in that condition as it can stall any time. Yes, a faulty/marginal internal diode (rectifier) in the alternator will cause the ouput voltage to drop and/or fluctuate.

[luedemann]

I had the car tested today at a different mechanic and he said that the alternator is charging at 15v. The mechanic said this is too high but when I talked to Nissan they just said it could be because of a bad battery but I know the battery is good. Any ideas?

[luedemann]

Okay, so the car is at 15.5 V with a load on - lights, heater, etc. I am getting another alternator put in (at a different shop hopefully under warranty still). What if the 2nd alternator comes back overcharging again. Would that mean that it is another defective alternator or there is another problem? Thanks!

[loystock]

Per spec, maximum charging voltage should be 14.7 VDC. Too high voltage may damage some electrical components/controllers.

[luedemann]

Okay, well the alternator comes in Monday so hopefully that fixes everything!

[luedemann]

Update - just replaced the 7.5 A Alt. S fuse under the hood and now it is not overcharging and the lights went out on the dash. Did I fix it ?!