Engine/Transmission (1994 - 1998) Won't Charge Batteries: Alternator OR PCM/voltage reg.?

[fortunate1]

Not an emergency, so this doesn't belong in "911". But returning yesterday from a job ~100 miles from home, the CHECK ENGINE light came on & stayed on. All guages are reading normally. Pulled over and shut down to check all the vital fluids, etc. All is good. Start back up and get onto the highway again - 5 miles later the light comes on again. Pull over & re-check everything. All is good. Get going again, and the light comes on after about 5 more miles. This time the voltage guage reads on the lowest side of normal, but definitely NOT near 14 V.



Once home, I put the trickle charger on the batteries for a few hours (not all night though). This morning the batteries showed 12. 34 V, the alternator (+ and - contacts) showed 12. 17 V at idle, and pin 20 of the PCM (other lead grounded) didn't give any reading. I may not have measured the PCM correctly though.



How can I troubleshoot this to see which is the culprit? If I have to buy expensive parts, I'd rather buy just one, not two.

 

[wcjp]

Sounds like an alternator. They're not difficult to remove and have tested. Free testing is better than throwing parts at the situation.



Also, just because an alternator test ok doesn't mean it's good. I've had bad alternator's on other vehicles that were great on the bench. When my 12V alt went bad it did exactly what you're describing.

 

[K5IP]

Your alternator is not working.

Regulator control functions are provided by the computer.

If you have 12Vdc across the field wires, the alternator should be charging.

The 12Vdc to the field is provided through the Auto Shutdown relay (ASD). The return side is a current sink provided by pcm and will read close to ( within a few volts of) zero when maximum charge is commanded.

The ASD is also enabled by the pcm and will not turn on ulnless the pcm knows the engine is running. This info is provided by the engine speed sensor. If your Tach is still working, the sensor is ok.

If you do have 12Vdc across the field, the alternator might still be ok but there is a large fuse, about 140 or 150A in the alternator output lead. Check it by measuring the voltage drop between the output of the alternator and a plus battery terminal.

Even if the alternator is bad it is probably just burshes.

Let us know how you are doing, or PM me. We can take it step by step.

Rog

 

[JFaughn]

Have the batteries load tested .

 

[Dfuruness]

I had the same problem and it was the alternator.

 

[fortunate1]

Leaning toward blaming the alternator. The tach works fine. So does the cruise control and a/c. Just making sure to keep the batteries well-charged after each day of driving. I also have a small solar panel with battery clamp connectors for the times when I'm not near an electric outlet. But I'll be buying a new alternator soon.

 

[Grizzly]

I would say it is the alternator also, however before you start purchasing anything try removing and cleaning all the battery terminals and make sure the cell are full of distilled water.

 

[fortunate1]

Done. The new alternator fixed it. Charging is at 14. 1 V now, and the CHECK ENGINE light stays off after starting. The only code now is 12, which is to be expected after disconnecting the batteries.

 

[K5IP]

Glad you got it and thanks for letting us know.

Rog

 

[Regcabguy]

Alternator Price

Who's got the best quality for the price for a new/rebuilt alternator these days? Thanks

 

[fortunate1]

Not sure of the best quality for the price, but this one (re-man) seemed pretty good. Price was $158. I saw some re-mans going for around 200. New ones ranged from 250's to 300. I got mine from an Advance Auto that's right in my small town, so convenience played a role. Plus I know the store mgr. fairly well, in case there's a problem with the alternator. The name was "Worldwide" #14430, and it came with a "limited lifetime warranty" that state the alternator will be replaced free of charge within 2 yrs. They must figure that the "lifetime" of an alternator is 2 yrs. Most of the others came with a 1 yr. warranty.



The original one lasted 11 yrs. We'll have to wait and see about this one. Fortunately, an alternator replacement is a pretty easy job.