2nd Gen Non-Engine/Transmission Low system voltage-help appreciated-many questions

[erobb]

Howdy folks,

Long time member, but don't get on here much any more just too busy, and the old truck just keeps going and going with very few problems. I got a new job last April that requires me to commute about 60 miles each way. My old truck that has been my trusty steed in my construction business since I bought it in 2000 was pressed into the daily commute, until I could see if the new job was going to work out. I was planning on buying some kind of rice burner after I got into my new job about 6 months or so which would be around Oct 1st. In which case I had planned to get her all detailed out and fluids changed and put her in the garage, and only use her for the occasional trip to the home improvement warehouse.

Anyway, on my way to the office Tuesday morning, my check gauges light came on and the voltage gauge was low and in the red, the other gauges were normal and the water temp OK, I thought maybe the belt had broke, but that was not the case. I originally thought of the alternator, and removed it and left my truck at work and borrowed my boss's vehicle to take home for the night. I stopped at a local O'Reilly's for a reman alternator, the counter person said we should check my old one 1st and it checked good. Confused, I returned the next day, re-installed the old alternator and the truck would not start, because the batteries were discharged, so we put a battery charger on it all afternoon. I was able to drive it back home on battery power alone, I have tried to have the batteries load tested but the tester just said, 'Undercharged'. I have it on the battery charger again at home now, so I will have the batteries tested this weekend.



I have checked the fuse box under the hood and everything seems OK, and have searched the web, so now I have more questions than answers.



1. Crankshaft sensor, I have read that if it goes bad the PCM won't tell the alternator to charge, but if it was bad wouldn't it trigger the CHECK ENGINE light?

2. Battery tray sensor, How can I test it to see if it's bad?

3. Voltage regulator in PCM, again if this fails wouldn't it trigger the CHECK ENGINE light, because mine is off. Also, there are rebuilt computers on ebay and the web for less than $200, are these quality units, has anyone ever tried one and from where? Does Mopar offer a Reman PCM? I could call the dealer but don't have my VIN with me right now.

4. I know it's way cheaper, but somehow just seems cheesy to do the 'External Regulator' thing. But seeing how I only need my truck to really get me through the next 2-3 months is probably what I will do.



I would like some advice on where to start diagnosing things, and how I can be certain it indeed is the PCM that's bad. I am going to most likely just replace the crank sensor and see if that helps, then go from there.



My father in law has a somewhat OK scanner, and on most vehicles it gives streaming data, but on my truck it will only read codes, the only code I had was po1692 (I think) 'system voltage low' when we tried to see the streaming data it said 'Cannot communicate with ECM' is this bad news, or is it just because it's a diesel and the data stream is different somehow?



I have found bits and pieces to this puzzle if someone could direct me to a good troubleshooting article somewhere it would be greatly appreciated, I do have the Haynes manual but do not have the factory service manual, yet.

Thanks for the help in advance. Sorry for the long post.



98. 5 Regular Cab, Laramie SLT, 4x4, 5-speed, 3. 55's, 275 Bosch Marine injectors, 4" turbo back exhaust, 375,000 miles, DRP lift pump on frame, Van AAiken box (until it crapped out last year does anybody have another one? cheap?)

 

[B.G. Smith]

Afraid I can't help much but to start off check the big terminal on the alternater and see if you get 12 volts there, If not the fusible link at the fuse box may be blown. oil filter is shanged bg

 

[erobb]

Thanks, that's one thing to check. I should easily be able to check that tonight. Will post back results.

 

[erobb]

OK, I tried to do a little more research before I left the office, and I'm not sure if I know more or not. When I got home I tested voltage to the big red wire on the alternator and I DO have 12. 5 volts on it. Also I read somewhere that one of the 2 smaller wires on the back of the alternator should also have 12 volts with the key on. So I checked that, I did NOT have 12 volts with only the key on. So just for giggles I cranked up the engine, then re tested and I DO have 12. 5 volts at the smaller wire on the right from looking at the back of the alternator. I guess the other wire is a control wire from the regulator, I had nothing on it. I was wondering if I could run a test lead to that terminal with the engine running to see if it kicks the alternator in?? If it does then I can just wire in the external regulator and be back on the road.



Also I have come to the conclusion that my crank sensor is not bad, as I have none of the usual symptoms of it, from what I read the engine will NOT start if the crank sensor is bad, mine fires right off, and it will also trip the CHECK ENGINE light, mine is off.



Also I charged the batteries one at a time one over night and the other while at work today. They both came up to full charge, my battery charger has a diagnostic thing on it, and it has detected several bad batteries for myself and friends and family over the years, it gave both batteries the green light, so I think it is just an alternator not charging issue.



I still wish someone would chime in with some more info. Thanks

 

[JR]

How old are your batteries? When they died on you at work was it because you left something on? That sounds suspect to me. It would be a good idea to have them load tested before you condemn anything else. Also go over your grounds and all the battery connections to make sure you dont have any corrosion or broken cables.

 

[erobb]

The batteries were both purchased new in 2009, I know they are 4 years old, the reason it would not start when I reinstalled the alt, was because I had driven it for who knows how many miles without the alternator charging.

I have also changed out the ASR relay with the horn relay, thinking it might be that, the horn relay had the same number on it, and I have honked the horn maybe 12 times since I owned the truck, it made no difference.

In the morning I am going to ground the other terminal of the alternator to see if it kicks it in. If it does I am headed to O'Reilly's to get a voltage regulator and wiring harness, I found the part numbers online.



I have checked grounds, and battery connections, no corrosion what so ever. Wiring in good condition.

 

[B.G. Smith]

I have a 99 Factory Manual, there is no trouble shooting guide for anything related to the charging system except the battery temp sensor which is under the drivers side batt. With the two wire disconnected it should read 9K to 11K ohms resistance. All other malfunctions of the charging system are supposed to set a code. Have you tried reading the codes? bg

 

[erobb]

Thanks for te help B. G. the problem is solved. Ever heard of a 'ripple test'? I never had, but that was what was wrong with my alternator. I am going to post another thread with the solution, I wonder how many PCM's have been condemned because of this.

 

[JR]

A basic ripple test can be performed with a dvm. I'm surprised it didn't fail when they tested it the first time?