Tcm grounding?

[wydopenLb7]

Hopefully someone can point me in the right direction. Have been dealing with the Allison in my lb7 either not going into reverse or going to 5th when I shift to drive and occasionally getting stuck in 5th or 1st. No codes but shift range inhibited on the dic when it won’t go into reverse. This has slowly progressed from an intermittent issue.

Fired up the parts cannon and put a new internal harness and nsbu in it which didn’t help. Chased all the wires visually and attempted to clean all the grounds. Wiring diagram shows ground zone 4 as the one im looking for which is passenger side back of block. I can’t seem to find it. Closest thing is battery cables to the starter solenoid. It shows that same ground T’ing off to the one on drivers side front of cyl head where the jump post is. Where is the one on the passenger side? Thanks for the help.

 

[2004LB7]

I might be wrong but on the LB7 I think that ground is actually on the driver's side where the battery ground connects too

 

[Ron Nielson]

The diagram covers several years, so keep that in mind. The notation on the ground on the driver's side shows that it is for RPO LB7. Jason is correct, as usual. That means that other RPOs will ground at the back passenger side of the block. It's a little confusing to interpret these diagrams at times.

I wonder if your ground problem might be a broken or almost broken wire that only shows up sometimes?

 

[wydopenLb7]

The diagram covers several years, so keep that in mind. The notation on the ground on the driver's side shows that it is for RPO LB7. Jason is correct, as usual. That means that other RPOs will ground at the back passenger side of the block. It's a little confusing to interpret these diagrams at times.

I wonder if your ground problem might be a broken or almost broken wire that only shows up sometimes?

Thank you. There were a few that were kinked inside the loom and I thought they may be broken. I stripped them back and they are intact. Guess the next step would be checking continuity between the connector on the trans and tcm. That was going to be my first step but haven’t had anyone to help. All the pins look fine. At first it seemed like it was happening when trans got up to temp so was thinking internal harness or bad ground but now it’s doing it on first start up. But then randomly won’t do it for a few miles.

 

[2004LB7]

Thank you. There were a few that were kinked inside the loom and I thought they may be broken. I stripped them back and they are intact. Guess the next step would be checking continuity between the connector on the trans and tcm. All the pins look fine. At first it seemed like it was happening when trans got up to temp so was thinking internal harness or bad ground but now it’s doing it on first start up. But then randomly won’t do it for a few miles.

Continuity testing isn't a very good test for these issues. Load testing is preferable.

Your issue almost sounds like the transmission internal harness going bad

 

[wydopenLb7]

Continuity testing isn't a very good test for these issues. Load testing is preferable.

Your issue almost sounds like the transmission internal harness going bad

The internal harness was the first thing I changed. Needless to say I was bummed when that wasn’t the issue.

 

[wydopenLb7]

Put the TCM in the freezer overnight and it worked perfect this morning. Going to make sure it's not working this afternoon when it warms up but I think that's the issue. If so is it best to buy a random one off ebay or is it worth the try on getting it repaired? If so where is the best place? If I buy a used one I will need to get it flashed at the dealer to make sure even if it's out of an LB7, correct?

 

[PureHybrid]

The TCM does contain the VIN, but you can swap it without issue. I'd reflash it anyway but that's just me

 

[wydopenLb7]

So I still haven't solved this unfortunately. Sent TCM in for repair. I had put it in freezer overnight and it worked perfect in the morning. Let it sit all day and problem was back on when I started it. Repair place said "circuit board issues repaired and internal faulty microprocessor and other components were replaced". Got it back and had every po700 code on first start up. Cleared them and worked fine until I parked and turned it off. Went to 5th instead of 1st when I restarted it and no reverse. Codes never came back. They had me try a global reset which didn't do anything.

Sent it back to the repair place thinking they didn't heat test it good enough. They said they couldn't find anything wrong but replaced more components just in case. They said they heat tested it. Got it back and same issue. Also all the po700 codes again on first start up. Cleared them and it worked perfect until I turned it off and back on. Codes didn't come back. Thinking it didn't make sense that they found problems with TCM but it wasn't causing my issues they told me to buy another TCM and they would refund me.

Bought a refurbished one flashed to my vin. Same exact thing. All the po700 codes on first start up, cleared them and it drove perfect for 40miles. Turned it off and same exact issue again.

Is the new nsbu I put on bad out of the box? Not sure if that would cause my problems being that it shifts fine until you turn it off and back on. Bought a load tester so I can test the harness but I don't want to go through all that if it's something simple I'm missing. The other thing that is throwing me off is that it got progressively worse and is now better but still doing it. Started as occasionally not shifting to R every time to that and an occasional weird shift to getting stuck in 5th even with OD turned off or getting stuck in 1st and never going into reverse and always going to 5th when shifting out of park. Now after replacing everything it works fine after sitting until you turn if off and back on. Almost like there is two things going on causing the same symptoms.

I have a feeling it's something simple I'm missing. Threw a bunch of $ in parts at it and am in the same boat.
Just so it's in one spot I've:

checked pins at tcm
checked fuses/grounds/wires for broken or rubbed through spots
replaced nsbu
new internal harness
new TCM

Thanks for any advice you can give.

 

[darkness]

Just for shits, pull the ign0 fuse. It’s in the driver door fuse panel. I don’t know if there is a set time to leave it out, but a couple minutes works for me. It’s “fixed” my trans from acting up twice. But so has replacing batteries and also the 4x4 selector switch.

 

[2004LB7]

Maybe log the TCM voltage to see if you are loosing it after driving. Have you verified your alternator and load tested the batteries. To me, it sounds like an electrical induced issue. Could be a bad line or ground causing voltage drop or fluctuations.

 

[wydopenLb7]

Just for shits, pull the ign0 fuse. It’s in the driver door fuse panel. I don’t know if there is a set time to leave it out, but a couple minutes works for me. It’s “fixed” my trans from acting up twice. But so has replacing batteries and also the 4x4 selector switch.

I'll give it a try..

 

[wydopenLb7]

Maybe log the TCM voltage to see if you are loosing it after driving. Have you verified your alternator and load tested the batteries. To me, it sounds like an electrical induced issue. Could be a bad line or ground causing voltage drop or fluctuations.

Batteries are fairly new and had them tested recently for a different issue that they weren't causing. Alternator is charging. I'll get them tested again just to be sure.

 

[2004LB7]

Batteries are fairly new and had them tested recently for a different issue that they weren't causing. Alternator is charging. I'll get them tested again just to be sure.

Still a good idea to log the TCM voltage. There is at least two line bringing power to the TCM. If one is flaky you can have all sorts of problems

 

[wydopenLb7]

So I load tested the tcm connectors and the pink wire, circuit 1020 would drop to 9.7v when under load. Was also able to read tcm voltage with new scanner and it showed the same. Replaced the wire and the voltage still drops. Under hood fuse box looks good zero corrosion. Put 12v to that wire and truck works perfectly. I’m assuming the problem is at the Incab fuse box which is a pain to deal with because the previous owner ran all the wiring for all the accessories on the 3rd battery through there and up the A pillar and you can barley get the fuses in and out let alone see what’s going on. Need to tow a trailer and I’m going to add a circuit with an inline fuse for now. Just want to make sure I am reading the schematic correctly. The pink wire is hot only at key on and the orange wire is hot all the time?

Thank you guys for the help on pointing me to the correct way to diagnose it.

 

[PureHybrid]

Appears to be that way, yes.

When you replaced the #1020 circuit, you ran two wires or just one new? No issues at the split coming out of the fuse box? "F10"

 

[wydopenLb7]

Appears to be that way, yes.

When you replaced the #1020 circuit, you ran two wires or just one new? No issues at the split coming out of the fuse box? "F10"

I actually just realized I highlighted the wrong wire. I did pink wire to pin 4. The other one didn’t drop under a load. You can see where I spliced in a new wire on the pink wire on the left. I’m assuming f10 is the wire to the right of that one and the next one must go to in cab fuse box.