• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

4L60E Electrical Issues

timw128

timw128

New Member
Messages
9
Reaction score
6
Location
Michigan
Hello-
1994 GMC C1500 2WD 5.7 showing DTC 66, 67, 81, 82. Appears to be no power to trans, started about a week ago intermittently, and now permanently. Find it extremely unlikely all 4 components tied to the above codes would fail at once. Suspect Ignition Switch (common anomaly) or ground faults. We have poked around a bit with DMM and noticed .7v drop at ECM/Ign fuse and Trans fuse with key on. Battery's at 12.56v static, 14v+ running.
Need ground locations for regular cab variant of above vehicle, please.
Any other advice, or questions, are appreciated and welcome.
Thanks in advance for any and all help.
Regards-
tim
 
Most all the ecm grounds are either at the rear passenger side of the intake, or the back of the passenger side cylinder head. The trans power is supplied via the ignition switch then through the 10 amp fuse in the interior fuse panel. The ecm then controls the grounds to actuate the trans.
 
THEFERMANATOR said:
The trans power is supplied via the ignition switch then through the 10 amp fuse in the interior fuse panel.
Click to expand...

Correct. The ECM then grounds to the thermostat housing, I believe. Have to figure out the voltage drop from the battery to the fuse block. The only thing in between is the ignition switch, and the grounds, of course. The main ground coming from battery to front intake manifold stud looks a bit suspicious. And I'll be surprised if there's anything left of the body/chassis grounding straps and engine/body grounding strap- the truck is 22 yrs. old and a Michigan truck. Michigan = salt in the winter. And plenty of it.
Thank you very much for your reply, 'THEFERMANATOR'. :)
Regards-
tim
 
Hey, Will K., thanks a lot!...seems highly applicable for these crazy times we're going through at present...HOOAH!
 
UPDATE:
Found a broken ground strap. Stud on front of dash captures a braided strap from frame rail, and back of engine somewhere- haven't checked location yet. The one to the frame rail was hanging on by a strand. Those straps are $5.99 and 18" long from Auto Zone. Think I'll run one from trans bell housing, back of engine(?), and frame rail to stud on front of dash. Could even run a redundant from stud to battery main ground at intake manifold. Cleaned main battery ground to front intake stud and pigtail to fender. Also ECM ground to thermostat housing. Guess we're making head way.
Next we'll check voltage into ignition switch and voltage out- key on, and engine running. Engine running we'll check the pink trans power lead and see if it holds voltage.
 
1st: Thank you for your service.

2nd: yeah GM has a long history of junk grounds. Upgrading size & quality of grounding is not a bad idea, nor is running the new cables tying in everythng like you're planning.

When its time to do the positive battery cable, upgrade its size and wire count also.
 
Will L. said:
1st: Thank you for your service.

2nd: yeah GM has a long history of junk grounds. Upgrading size & quality of grounding is not a bad idea, nor is running the new cables tying in everythng like you're planning.

When its time to do the positive battery cable, upgrade its size and wire count also.
Click to expand...

1) You're very welcome... 46 yrs. later, I still see no point in the 'Nam/Cambodian affair. Except a lot of people died so the ruling class could make more money.

2) I'm still trying to figure where the trans grounds- someone said elsewhere there's a braided strap bundle with the starter wires running in a metal insulator tube. Haven't made it to the basement of the truck yet...LOL!... frankly, I would assume the trans grounds to the engine via bell housing bolt proxy.
The nut that threads to the front of dash stud won't come all the way off because the stud's stripped near the end... soooo, now we have to crawl up in there and cut about an 1/8" off the end of ground stud to get nut and ground strap terminals free. Lovely!... more LOL!...I'm too old and too busted up for this brand of gymnastics!...final LOL! (for now!)

I sure appreciate all the input...We'll keep updating through to resolution so that this thread will help someone else down the road. Apparently, these electrical issues and their effect on the 4L60E from that period are fairly common.
I'm not going to put on the hat of a 'parts installer' and start throwing parts at it. Cause and effect- find the problem, fix the problem. That's what a true mechanic does. Too many professional parts installers out there nowadays.
I guess my years as an Engineer at GM might get me through this. The ignition switch on these is undesirable, long term, as it is of the piano key contact design...overtime, the pins that supply 12v signal to trans (among other paths) become inefficient due to carbon build up from continuous arcing. There's a $120 relay kit out there that eliminates the GM ignition switch issue, forever (well sort of forever!), but it's merely a band aid. You can make your own Power Relay system for about $20 from parts at the out parts store. Here's a graphic of it-

http://s1092.photobucket.com/user/timw128/media/power_relay1.jpg.html

Kind Regards-

tim
 
Had a 93 that gave me all kinds of problems before. Pulled the loom off the harness and found all the wires melted together. It was a farm truck and combo of cow manure and oil melted the insulation on the wires all together into a big blob. Had to replace 4 feet of wire from the trans forward to fix it.
 
THEFERMANATOR said:
Had a 93 that gave me all kinds of problems before. Pulled the loom off the harness and found all the wires melted together. It was a farm truck and combo of cow manure and oil melted the insulation on the wires all together into a big blob. Had to replace 4 feet of wire from the trans forward to fix it.
Click to expand...

Well, these dad gum things aren't the easiest to work on... just high enough from the ground to make bending over the fender a pain. Back in the day, Chilton used to make nice hardbound repair manuals for vehicles, with complete wiring diagrams and hose routing. Can't get them anymore, except those cheap, low information paperback deals. Chilton wants you to pay them so much a month for online access to their data banks, and then you have to print off what you need.
I liked the world better back in the 60's. A vacuum gauge, dwell meter, and a timing light is about all you needed to work on cars then.
Do you know where I can get a wiring diagram for this truck?...
 
I use alldatadiy as they give you the factory manuals(mitchell doesnt always give you factory manuals). If you want the actual manuals, you can check ebay as they pop up from time to time on there, or else you can order them from GM, but I believe its about $175 for the full set per year.
 
THEFERMANATOR said:
I use alldatadiy as they give you the factory manuals(mitchell doesnt always give you factory manuals). If you want the actual manuals, you can check ebay as they pop up from time to time on there, or else you can order them from GM, but I believe its about $175 for the full set per year.
Click to expand...

Yeah, not paying that kind of money, nor paying that monthly online fee... thanks, though.

OK, replaced ground strap from firewall to frame. Couldn't get to the bolt on back of block on passenger side, but strap is solid- ran a 10ga redundant from main battery ground at front of intake to firewall and ties to others.

Cleared the codes. Started truck, put it in gear and it hit pretty hard. Still have limp home mode. Don't think it's the ignition switch now, as I'm getting 14.02v at back end of trans fuse with engine running.
Sooo, tomorrow I guess will get under truck and hunt down trans ground strap, if there's such an animal- you'd think the bellhousing/block interface would form a ground. Going to check for voltage at the trans connector (pin 'E', pink wire).
If don't find anything there, perhaps it's time to investigate the solenoids, or even the internal harness. Sure glad I have that external connector pigtail that we picked up at the bone yard. Probably should check the codes again first thing.

Oh, yeah, have to go back to 'chevychase's' sticky about the wiring diagrams and study some more.

Thanks-

tim

EDIT!- OOOPS, SORRY!... 'chevychase' is a mod over on Truck Forums...now I got my darn wires crossed!...LOL!
 
I've got to chime in here and put a word in for the importance of grounds. I'd read on this forum about how important it is to make sure your ground wires are all good and have clean connections, but I was surprised that it would have as much effect as it did. When I had the front end all apart to replace upper control arm bushings and one bad ball joint(did the brakes and replaced the brake hoses while I was there along with lubing wheel bearings, new sway bar bushings and links, etc, etc), with the wheels and all out of the way the ground wires that are in that area were visible and easily accessed. I cleaned them up, and searched out the rest and cleaned and reconnected them, with new star lockers where there were old rusted up ones. EVERYTHING ELECTRICAL works better now. The engine seems to run better - acceleration much improved, the trans shifts smoother, the lift pump sounds like I put a new one on when I turn on the key, and that together with the glow plugs maybe getting hotter, it is starting better. The radio even sounds better and I get more stations - really!
Everything I've done to the truck has made it better in one particular way or another, but there is an overall improvement of many little things that has improved the whole truck driving experience. Simply cleaning the grounds made a big difference in the enjoyment of driving the truck. I had $68k Ram Cummins blah, blah, blah trucks that were beasts, but I grew to hate getting in them(especially the HO 2012) to go somewhere - good for work and towing, sucked for anything else. This truck is now just plain fun to drive around like none of the others were, even with a seat that looks like a hungry bear tried to eat it for lunch.

Everyone with a 6.5 diesel (maybe all GM trucks) - CLEAN YOUR GROUND CONNECTIONS!!!!!! I'm thinking of putting a "happy face" sticker on the back of the truck (just kidding).
 
  • Like
Reactions: NVW
Beginning my seek of elec gremlin on 4L60e in express 2500 5.0 ‘97, slips after 2nd. Moving engine fuse block inside and stripping loom from harness, inspecting grounds. New solenoids, tran harness, VSS, ign sw...
 
You must log in or register to reply here.
Back
Top