Mechanics

BATTERY LIGHT STAYS ON

2000 Dodge Caravan • 124,000 miles

I have a 2000 dodge grand caravan sport 3.3L flex fuel. The battery light stays on I have replaced Atlernator and battery and I still have the same problem I have 12 volts to the alternator when the key is off. At the battery when the engine is running I get 13.6 and with everything turned on I get 12.9. Is there two fuse links that go to the PCM from the alternator to the PCM regulator. Or could it be the battery sensor under the battery. I had to have the PCM reporgamed due to it had locked up and would not pass safety inspection.


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TroyGraham
June 3, 2012.



Did you verify powers and grounds for the alternator>> basics first.

13.6 under a load is not bad at idle. Should jump to 14 with 1500 rpm. Check the fuses for the light.

What was the issue with the old alternator? The pcm does control alt output.

Roy

Yes, I have 12V at alternator and I checked all ground cables. They where ok.

Tiny
TroyGraham
Jun 3, 2012.
Hi guys. You need to check the voltage on the two small wires on the back of the alternator but that has to be done with the engine running. One must have full battery voltage. The other one must be less but not 0 volts. Holler back with those numbers.

Caradiodoc
Jun 3, 2012.
On the small wires I get 9.5 at idlle and 12.5 at 1500 rpm the other wire I get no voltage reading.

Tiny
TroyGraham
Jun 16, 2012.
Can you see the wire colors? Less than battery voltage is normal on the dark green control wire but it must not be 0 volts. If that 9.5 / 12.5 volts is on that wire, that part of the system is working and you didn't make good contact with the probe on the other wire. It had to have full battery voltage for there to be anything on the one you found voltage.

If that 9.5 / 12.5 volts was on the dark green / orange wire, that is the 12 volt feed and what you found is too low. Since that circuit runs injectors and ignition coils and is obviously working, that leaves a corroded splice as the likely suspect.

I think the first scenario is the one that pertains to your van because to actually have 0 volts on the dark green control wire, that wire would have to be grounded or the brushes inside the alternator would have to be worn and open. Worn brushes are common but not on a replacement alternator unless you installed a used one. If that wire was grounded, the system would be charging wide open and you'd be having an overcharge condition. Either way, this would imply there are two different problems.

Assuming the first story is right and you found that voltage on the dark green wire, measure the voltage on the fat bolted-on output wire. If it's real high with the engine running, as in 16 or more volts, there's a break in that wire going to the battery. Look for a blown large bolted-in fuse under the hood. You will also find 0 volts there with the engine off.

If you find full battery voltage at the alternator output terminal all the time but it's not making it up to 13.75 to 14.75 volts when the engine is running, suspect a failed diode inside the alternator. That can be identified with a professional load test. Most of these were 90 amp units. With a failed diode you will lose two thirds of its capacity and only be able to get around 30 amps. That would explain why the system voltage was dropping to 12.9 volts with many things turned on. The alternator can't keep up. That low voltage will turn on the "battery" warning light. Most load testers also display a bar graph to show relative "ripple". Ripple will be very high with a bad diode.

Caradiodoc
Jun 16, 2012.