Intermittent abs/no speedo/no shift

[alexd_NJ]

Hey guys, new to the forum but I have been lurking in the shadows for a while now, have 3 gmt800 trucks...

 

Looking for some advice here as I’m running out of hairs to pull out. 2003 Silverado 1500 4wd 5.3 z71 184k; I bought the truck from a buddy of mine knowing it had its gremlins but I bought it for a winter beater and paid less than the price of a new iPhone. The truck has the beloved intermittent abs brake light, no speedometer and won’t shift unless manually shifted. He took the truck to a shop here in town, they replaced the hubs, vss and pigtail but the issue persisted. I bought it and went over what they had done as well as adding a delco ebcm, cleaning the ground on drivers side body mount bracket and moving the ground from the back passenger side of the engine. Truck was good for 200+ miles then issue persisted but randomly, until yesterday. Start up and drive to get coffee before work, no speedo no shift and brake light. Go inside get my order restart truck-boom like nothing’s wrong truck functions well. Same thing after work start it after 12 hours of sitting lights on issue persists, stop for gas restart truck no issue. Repeated itself again this morning on my way in to work. It’s intermittent and seems to now clear itself when shut off for 5-10 minutes. SOS if anyone has any input, I’d gladly appreciate it. I called a local “automotive electrical expert” he gets $180 an hour. 

[sefiroxx]

$180/HR - I know what I want to be when I grow up


Problems at startup that go away when warm start , sounds like wiring problem (short/ground) that goes away when moisture is burned/shaken off.

Transmission shifting. When you say manually shifted, do you mean you are moving up thru the gear shift lever , 1,2,3,D or other. What are rpms when shifts hit?

The ecu uses inputs from vss, tps, current gear and possibly abs to instruct tranny to shift and when. A good tranny shop should be able to tap the harness to confirm a) gears shift on command b) proper signals from the ecu.

[rjgti]

I have the same issue I am working on.  1999 5.3 autotrac.  lose all gears except 1-2. abs and brake light on. no speedo.  4hi work as well as 4 lo, but no autotrac(due to abs).  had my scanner on it and caught an episode.  rear wheel speed erratic. front right wheel speed erratic.  vss code. trans in limp mode.  also noted at that startup that battery voltage during crank was 7.5 volts.  will get back at it on wed as my wifes car broke a steel brake line that I am currently fixing

[rjgti]

thinking it may be a battery cable issue or ground or battery. will look more on wed

[alexd_NJ]

14 hours ago, rjgti said:

thinking it may be a battery cable issue or ground or battery. will look more on wed

I’m thinking the same thing, last 2 days it would act up. Shut the truck off lock and close the door, open with key would and start. No issue. Today however that’s not curing the issue, I’m seeing a voltage drop on the dummie gauge and a rough idle every so often. Truck actually stalled on me when putting in park...went to Lowe’s and bought 4 feet of 6 gauge wire and 2 lugs. Will move drivers side firewall to block ground to the alternator bracket and see how that works. The autozone in town has a negative battery cable in stock, may also go pick that up. 

[rjgti]

mine is solved. tcase snapring on output shaft broke. hour later it is working perfectly

[alexd_NJ]

1 hour ago, rjgti said:

mine is solved. tcase snapring on output shaft broke. hour later it is working perfectly

How entailed was that to do? I was starting to think that was my issue or the bcm. I wonder how the snap ring came into play with 7.5 volts at start up?

[swathdiver]

Bad cell in battery and or low voltage can cause all kinds of electrical gremlins in these trucks.

[alexd_NJ]

1 hour ago, swathdiver said:

Bad cell in battery and or low voltage can cause all kinds of electrical gremlins in these trucks.

I’ve got a brand new battery from my Tahoe and 145amp alternator that’s apart right now for a cracked 706 head. Maybe I’ll put them in this truck and see if it straightens out 

[swathdiver]

2 hours ago, alexd_NJ said:

I’ve got a brand new battery from my Tahoe and 145amp alternator that’s apart right now for a cracked 706 head. Maybe I’ll put them in this truck and see if it straightens out 

Not a bad idea, just do one at a time.