If you were having to replace an ecm, who would you recommend purchasing one from? I think mine may be on the way out. I was driving long distance this weekend and my "check gages" light came on. I noticed that my volt gauge was showing lower charging than usual. I stopped at a parts store and had the voltage checked with the engine running. It showed 13 volts. I could shut the truck off overnight and the next morning it was charging like normal and the light was off. If I drove it for a while and then shut it off, when I started it(while truck was still warm) the light would come back on and it showed low voltage again. From what I can tell, this can be a sign the regulator in the computer is going out. I was able to drive the truck about 200 miles home. I could tell the longer I drove, the lower the reading was on the gauge. Funny thing is it would still start with no problem.
I replaced the alternator as soon as I got home. When I started the truck, it still showed low voltage on the gauge. I only let it run for about 30 seconds and I shut it off. I put a charger on the batteries overnight( they showed to be pretty low). The next day I started it, the light was off and it charged normally. I drove it off and on all day with no issues. I just drove it 75 miles to work this morning with no problems either. I just feel like it's going to do it again though.

Could the alternator have been the problem. I wouldn't think so being the new one didn't show to be charging any better than the old one(even though I only ran it about 30 seconds before recharging the batteries). I did have 461,000+ miles on the old one though.

thanks
Dave

 

ECM is programmed to the individual truck and has to be done by the dealer.

You are jumping the gun and throwing parts at your truck without doing any diagnosis.

Check the codes, check the batteries, check all connections including grounds, check the resistance of the battery cables, especially the one connecting the two batteries.

The alternator charges the passenger battery and the ECM takes its reading from the driver's side battery. If there is resistance in the cable or connections the driver's side battery doesn't get fully charged and the passenger battery can get overcharged.

Some trucks also have a temp sensor under each battery that can cause issues.

 

The voltage regulator is in the TIPM, not the ECM. Just wondering, have you thouroughly cleaned all your battery connections? I had electrical gremlins for 2 years before I finally figured it was invisible corrosion on the connections throughout my charging system. (i wrote another thread about it)

 

It's the ECM who regulates the field current of the alternator.

 

Redo ALL your battery connections and grounds., clean and tight.
Make sure the crossover cable is good.
You might have over 16V on passenger side battery and less than 13V on driver side battery when the crossover cable was defective.
The voltage you see on the dash was the driver side battery voltage.
Nothing wrong with your ECM and alternator at this moment.

 

Thanks for the replies. I already had the replacement alternator sitting on a shelf at home so I went ahead and tried it. I was on the road driving when the light originally came on. I did the key cycle trick and no codes showed at the time, just displayed ----done----. I drove it Friday evening and the light stayed on. When I got in it Saturday morning, the light was off and it was charging normally. Still no codes. I drove for about 30 minutes before shutting it off. Later in the day when I got in it to drive home(about 200 miles) the light was on again and it was showing to not be charging correctly. After getting home, I tried the new alternator. As soon as I started it I could tell it was still not showing to be charging correctly. I just shut it off and put a battery charger on it. The batteries definitely were low according to my charger. I left the charger on all night and tried it Sunday morning. The light was off and it has been working fine ever since.

One thing, I did check the codes again Sunday morning after replacing the alternator. It did have some codes stored at that time. When I changed the alternator, I did forget to plug in the map sensor. I noticed that Sunday morning when I started it. The engine light came on and that's when I realized I forgot to plug it in. The engine light went out after starting it several times that day but it still had the codes stored. But there were other codes stored too.

Here's a list of codes. I'm thinking these two are from the map sensor being unplugged.
0073 (ambient air temp sensor circuit high)
0107 (manifold pressure sensor low)

charging related
2502 (charging system output voltage)
0622 (generator field control circuit)

and these two (don't know why they showed up at this time unless it's a coincidence)
0713 (trans temp sensor 1 high)
0483 (cooling fan speed)

This morning(Tuesday), I checked the codes and there are none stored at all. Just showing ---done--- again.

I did clean and check all connections before I replaced the alternator.

It's weird that all codes are gone now. Truck is running great.

Thanks
Dave

 

Just cross your fingers and see.........

 

+1 on checking your grounds. The negative battery cable is known for losing contact with the frame and can wreck all kinds of electrical gremlin havoc. Easy fix though.