Hi folks, today my check engine light came on and the alternator quit charging. I've seen other threads where the PCM went bad and an external regulator was installed. I have checked the 2 small wires going to the alternator and don't have voltage to either one, is this a classic case of PCM failure?

 

Did you lose your Tach as well?

If not, you need to have your Alternator checked first.

 

Tach works when it wants to, but today it was working when this happened. Never had a problem with it not charging when the tach was not working.

 

Ok, somewhere in the systems you have corrosion or a bad pin contact.

I would look at the connector to the PCM first.

 

If the Tach is intermittent, then I would be checking the Engine Speed Sensor as another did just in another thread. IF the PCM senses a erratic pulse from the ESS it will shut down the other circuits it controls.

 

What circuits are controlled by the PCM? The "other" thread mentioned the alternator and air conditioning, well my A/C has never failed to blow cold air whether the tach is working or not.
Tested Alt by unhooking harness except large batt. wire, grounding one small terminal and hooking the other to batt +. Old alt. didn't change voltage at all, tested new one when installed and it put out almost 25VDC
Oh, by the way, I now have a working charging system and cold A/C, all of this with a dead tach

 

Sorry to hear, there wasn't any mention of the AC system.

I've repaired the alternator with a set of brushes, pretty cheap.. Also they do start to stick and can be cleaned. I just did that last fall to the new alternator I got a couple years ago.

 

Could also be your Tach or circuit on the dash. Your PCM could still be getting the pulse from the sensor.

 

I figure it is most likely the sensor, the tach bounces at anything under 1K RPMs when it is working As long as everything else is working I really don't care if the tach works or not Been running this way for probably the last 100K miles.

 

If you have a check engine light on it will set codes.
Check them with the method described here> http://dodgeram.org/tech/dsl/trouble..._DTC_codes.htm

 

Thanks, I'll check them, unless they cleared when I had the batteries unhooked for several hours when I replaced the alt. Bad thing about living out in the country and being self employed, you really never know how long that trip to town will actually take