Hi,

Right after the annual state inspection in NJ, the battery light on the dash-board came on and pulled out the code:

Code 41- Circuit: Alternator field not switching properly.
Code 41- Description of fault condition: An open or shorted condition detected in the alternator field control circuit


I just got a new battery about 3 months ago.

The battery volts without car running: 12.54v
The battery volts with car running and speed up: 12.6-12.8v

from the error code 41, is it the alternator going bad or EVR in the PCM or something else?

TIA.

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97GC v6 3.0 engine

 

I have the pdf file for testing code 41, if you want it just send a email. The PCM controls the voltage between 12v to 15v.

 

Hi Master,

Please forward the pdf for testing code 41. thanks.

 

Mine came on before and it was the terminal for the positive connector on top of the alt. had some corrosion on it. I cleaned it off and it's been fine ever since. Alternator is not easy to remove, you have to pull the wheel & splash shield to access the lower bolt(s), but I would pull it and take it to autozone, etc, they offer free testing... You should have about 12 volts with engine off, 14+ with engine running. But check all the cables and connections first for corrosion

 

Checked everything out ok. Now the battery light does not come on again, but the battery posts volt is about 12.40 V when car is idling. Also a few times when the van started cold, it reached 13.6V at battery posts,
as the car warms up, the battery posts volts decreases to 12.0 - 13.0V.

is the above normal or some trouble waiting to happen?

here what I checked:

1. loosen the alternater B+ end and battery positive + post end, checked continuity: good(got an audible sound) and it has 0.2 ohm.

2. disconnected the nippondenso field wire plug:
a. checked field wire(green:#2) to pcm #4 for continuity: good with 0.2 ohm.
b. checked ASD wire at alternator(green/ori:#1) to asd relay socket #87 for continuity: good with 0.2 ohm.
c. checked ASD relay #87 to PCM #6 for continuity: good with 0.3 0hm.

3. checked alternator two posts(green and green/ori) within the field plug for continuity: good with 2.3 ohm. this falls in the correct values.


with the two field wires(green and green/ori) jumpped for testing:

4. full field test: with the van idling with all lights and fans on, grounded the alternator filed wire(green/#2) and seen the battery posts voltage increases from 11.50V to 13.8V. This proves the alternator is good, isn't it?


5. with the van idling, checked the alternator field wire(green/#1) for DWELL, it has a different value of 22.3 verses 45.2 when the van was not running. This proves the PCM is putting out a value, then the PCM is not broken, is that right?

6. with the van idling, asd wire at the alternator(green/ori, #1) has 12.7v which is the same as the battery voltage.

7. with the van idling, the field wire(green, #2) has about 9 volt.

 

Master Tech, Thanks for the pdf and I was able to match the alternator wires to the pcm.

You mentioned that the PCM controls between 12v-15v. so is this true?:
when pcm sees the battery voltage reached 12.6v, then it lowers the alternator output voltage to below 12.6V until the battery voltage goes below 12V, then the pcm commands the alternater to output 13.6v to charge the battery again until it reaches 12.6V.
then it goes to the next cycle on the low end.

thx.

 

The charging system is proected by a 10 gauge fusiable link located in the A11 circuit is connected to the battery feed bus bar of the PDC and the generator. The generator is case grounded through its attaching bracket. This generator uses a voltage regulator internal to the PCM. When a vehicle is running, battery voltage is applied to the generator field terminal through A142 circuit. This circuit is controlled by the contact side of the ASD relay.The ground, or voltage regulated side, of the generator field is controlled by the K20 circuit. The K20 circuit connects to cavity 4 of the PCM. I hope this helps you. If you had a DRB3 you could do a full field test.

 

Master Tech and others,

First thank all for the postings.

In one test I found that there is no continuity between the field driver wire(green) and power wire(green/org) in the alternator, then took it off, opened it and found there was a lot of dirt between the slip rings and the brushes. Cleaned up and put it back and now it's working like new. But noticed that the brushes and slip rings medal coding are fading. Anyway glad to find out the root cause. Especially thanks for the pdf file Master Tech shared, without it I would not be able to determine the alternator is the culpret. Ordered a brush set from ebay and will replace it when receive it.