I recently got a Check Engine Light and my in dash volt meter now reads around 8-10 Volts. So I checked the code and its Code 41. (Generator field not switching properly) So I'm curious - what order of things and how should I start trouble shooting the Problem?

From searching it looks like the most common problems are:

Alternator - I haven't pulled it off yet to go get it tested, but plan to tonight.

Voltage Regulator - Mine is a '92 so it doesn't have one on the firewall.

PCM - How do I test that?

Crank Position Sensor - Mine appears to be set correctly with 1/16" gap.

Or random wiring problem which is probably the case since my harness is falling apart all over the truck.

 

Having had it happen already, I'd say your alternator is probably worn out, especially if its the orginal. It could also be a PCM, but they only seem to misbehave in the cold.

 

Since I forgot to ask above - Can it throw a code 41 "Generator field not switching properly" if JUST the alternator went bad? Just seems like to me if it throws a code - it seems like the PCM doesn't realize the motor is actually running maybe to let the alternator charge??? then again, I'm still not sure how this whole system functions.....

 

Swap the front two relays on the driver's fender and see if it clears up. Code 41 can be set by either a short or an open in the field control circuit. It's not a real specific code.

 

I'll try that...

What do you mean by "field control circuit." Is that listed as such in the wiring diagrams? (I haven't looked myself)

 

I'm a little fuzzy on what they mean as well. It should be the wire from the ground side of the field to the PCM, but they may be including the ASD relay driver in that because it "controls" the field by turning on the power when the PCM gets a crank speed over 400 RPM.

 

Okay now I'm confused after working on it tonight!!!!

Before I started doing anything, I fired it up (motor cold). Dash volt meter read 8-9 volts depending on the cycle of the grid heaters. So I unplugged the control wires to the relays and put a Volt meter on the battery terminals. It read about 10 Volts. Then I wiggled around on the Crank position sensor wiring and got no change to battery voltage.

Then I turned the motor off and pulled the alternator and took it down town and got it tested. Tested out Okay and it produced 15.2 volts on their machine. Seemed a bit high to me, but thats not the problem I'm having....

So then I got back home and checked the crank position sensor hieght - it was around .035" as best as I could tell because it was pretty dirty. Then I removed the sensor (and cleaned it off) and used an ohm meter on each one of the three wires by probing through the insulation near the sensor and then the metal prongs in the plug. every wire checked out good and no matter how I moved and flexed the wires, it still had continuity. I also check for shorted wires and I found none.

Then I checked for continuity on the engine harness from the plug near the front of the head front to the set of two large plugs (one gray and one black) near the back of the head on the driver side. Those wires check out okay.

Then I removed the main plug from the PCM (which I assume is that black box behind the driver side headlight) and check for continuity and those check out good also...

Figured there was nothing else I could check, I decided to put it all back together. So thats what I did and I fired it back up to test to see if it still wasn't charging the battery.

Well it was charging.... HUH.... So I took it apart ans found nothign wrong and put it back together and now it works... The dash gauge now reads 12.5 volts and a volt meter at the battery terminals reads 14.9 - 15.0 volts.

But wait - theres a twist. Not only did it fix my charging issue, my heater fan now works (it didn't before), the power windows are now working (they didn't before) and the warning lights 'water in fuel' and 'wait to start' are now off like they should be (they were on before). Oh it also quit showing the check engline light. So not only did it fix the charging issue but it fixed all these other issues as well.

Does the PCM cut power to other non-essential circuits when there is a charging problem?

 

Sounds like you fixed a ground connection somewhere that wasn't working before you tore everything apart.

 

Sounds like you missed where I said:

I tested it before I tore it apart and it wasn't charging.
So I tore it apart and found nothing wrong.
So I put it back together and now it works.

The only ground I disturbed was the ground tab on the alternator and the battery ground.

 

If I had a nickle for every time I "fixed" something without being sure exactly what it was I did to fix it...

 

The only things I can explain are the charging and the idiot lights. Sounds like the PCM connector was cruddy, that was the cause of the code 41 and no charging.

 

My wait to start light stuck on and the alternator quit, so im gonna go unplug the pcm and cross my fingers.
-RATCHET-