Codes: P0622, P1637.
came up from charging system fault. New battery. checked the output from the alt. and was getting 5.5v. Replaced alt. and same readings, but these codes. Checked starter wires, good, battery and alt. connections good. In the recent past i have had high voltage come up while driving.
I understand that the pcm determines the voltage output of the alt. depending upon demand. Radio, a/c, lights off, 5.5v. everything on, 5.5V. Just where do i go from here? Do i need to replace the pcm? has anyone had this happen? if so, what direction do I need to go?
Situation is getting serious, car cant go anywhere as the battery is the only power supply with no charging from the alt.
This is the second post, just more detailed.

 

Back in the day, EVIL TWIN use to be the ALTERNATOR EXPERT and knew all the ins and outs on this system. He was answering post a few months ago. PM him and see if he can provide you some more assistance.
There are several types of GM alternators that look and smell the same but the PCM wont recognize. The PCM is looking for the exact same type of alternator that originally came out of the car. If you have all the proper connections on the alternator, the battery is good and the connections are clean and tight, that could be the issue. Do you still have the old alternator??

BC

 

the original alt. is back in the car. But the replacement was the same brand, and read voltage the same as the original one I re-installed.
Doesnt the pcm send the signal to the voltage regulator to increase or decrease charge as load requires?
By the way, thanks for coming on this post. I wasnt going to ask you outright, but hoped you would get involved.

 

Brand doesnt matter. The model number needs to be the same. Has a lot to do with the current output if I remember correctly. If there the exact same modela and series, then theres something else that were not seeing.

When the car is OFF, what voltage do you read on:

The alternator field connection (large terminal nut on the back of the alternator) to ground ?

The battery POS terminal to ground?

When the engine is running what voltages do you see at the came terminals???

BC

 

I have only checked the battery pos when the car is off. it is reading around 10 now. it has been drawing from starts/stops since this started.

Bill, what do the codes tell you? generator F/field terminal circuit,
generator L/terminal circuit?

 

did some more testing last night, and by mistake I have found the trouble "area".
Checked voltage when the car was not running, but had been sitting since the night before. I had 12V at the alt. terminal, 12V @ the battery. Started the car and read 5.5V at the alt. and 12.5 @ the battery.
Rechecked the wires going to the starter, they were tight. Sat back and thought about it for around 10 min., rechecked the alt. with the car not running and I read 12.4V @ the alt.
After this, I had the test leads on the alt. and I asked my son to atart the car. The second that he turned the key to the start position the reading @ the alt. dropped to 5.5V from what was 12.4V.
I am not positive but I believe the starter solonoid must have a short in it that is causing the problem.
Anyone want to chime in here, your more than welcome. I REALLY dont want to have to remove the headers to swap the starter, but......

If someone else feels this IS the problem, then Jason....you better give me a price to replace the starter. You have the lift, I dont.

 

Andy,

If you have a set of jumper cables, try clamping somewhere on the case of the alternator and clamp the other end to the negative post of the battery. Start the engine and check the voltages again. This is a quick check to identify a ground issue. If you find the voltages return to normal with the jumper, then you have a ground issue.

Regards,

Eric D

 

You don't have to remove the headers to get the starter out-I did it in 1.5 hrs,the only thing was I had to bend a piece of frame to get the starter out,no biggie....

 

anyone have an idea if this sounds right from what I found last night?

 

Eric D is 100% correct! If you attach a jumper cable from the POS batt terminal to the field connection on the back of the alternator, you can bypass all the wiring at the solenoid and you should see charging voltage at the battery when the engine running if everything else is good in the alternator.

If you do see correct charging voltage once you attach the jumper,,,the wiring between the battery / solenoid / and alternator is very suspect. Remember. If you have a BAD connection, under a NO LOAD condition, you will see 12 VDC. Once you load the circuit, the bad connection turns the poor connection to a (resistor) and you see a reduced or NO voltage condition. The starter/solenoid could in-fact be fine. Its easy to check the wiring.

If you examine the wiring at the solenoid, you will see that the wires are spliced. Those ugly splice looking things are IN LINE FUSIBLE LINKS and the colors of the wires changes AT THE SOLENOID. So, don't be surprised when you see that. If everything looks good, disconnect the wiring and use an OHM Meter to measure the resiatance oe each wire through those fuse links! You should see cloase to ZERO ohms on a good wire. If you see anything above 2 or 3 ohms, that wire/fuse link is suspect.

If nothing else, just remove all the wiring, examine it, clean it and reconnect it.

BC

 

thanks everyone, have been out of touch. I will try this and go from there.