Slow to shift 2003 LMTV

[Delta24]

Hello all,

Brand new to the group....just picked up my LMTV a couple days ago and have been just kinda going through it. Few issues need addressed.

The first and most important is the transmission is slow to shift. The engine spools fine, but the trans just doesn't seem to want to upshift. It will eventually....but not when it should.

The only code on the trans controller is 1323. I cleared the code via the controller and no change. Trans appears to have transmission fluid in it, not engine oil.

As a test, I shifted manually. Started in 2nd....revved the engine to max rpm, and up shifted. Shifted firm and immediately. It did so for every gear. Do these trucks have a TPS (Throttle position sensor)? Forgive the possibly dumb question....brand new to trucks this large.

Regards,
Jason
Rhome, TX

 

[Ronmar]

1323 is a high voltage fault(over 35V). Only that code in the D1 thru D5 memory locations? You use mode to step thru the 5 memory locations once in diagnostic mode(both arrows)…

They do have TPS and it does play a large part in shifting. On the A0 it us a standalone unit on top of the engine. 2003 sounds like an A1, and the A1 gets TPS info from the ECU via the data bus. that would be my first check for what you describe(shifting at RPM limit). Probably going to need cat or allison software to access TPS real time info on an A1 though…

 

[Delta24]

1323 is a high voltage fault(over 35V). Only that code in the D1 thru D5 memory locations? You use mode to step thru the 5 memory locations once in diagnostic mode(both arrows)…

They do have TPS and it does play a large part in shifting. On the A0 it us a standalone unit on top of the engine. 2003 sounds like an A1, and the A1 gets TPS info from the ECU via the data bus. that would be my first check for what you describe(shifting at RPM limit). Probably going to need cat or allison software to access TPS real time info on an A1 though…

Ronmar, thanks for the reply. Yes, 1323 was the only code. I've driven it a couple times short distances (less than 5 miles) the past day or so. Previously, I cleared the code...and checking just now, it hasn't returned.

Frankly....I'm kinda wondering if what I'm experiencing is normal. I got up to 40 today....and heard a pretty awful noise...to me sounded like a wheel bearing getting lunched. Back in the shop, and I see I have a forward u-joint that has a bit more slop in it than should. I'm very hesitant to put any "real" speed on the truck with the existing tires. So, I'll change the ujoint and tires and see exactly what it does.

Again, thanks for the reply!!
Jason

 

[NDT]

Check your u joint phasing! Wrong more often than not.

 

[Delta24]

Check your u joint phasing! Wrong more often than not.

Whelp....mine are 90 degrees off. One more thing to fix. Thanks!!!!

 

[NDT]

That is your awful noise.

 

[Ronmar]

And probably why your u-joint isn't happy...

 

[GeneralDisorder]

Yes you best correct the driveshaft phasing before you wreck the transmission, differential yokes, and possibly a lot more. I wouldn't move the truck till the driveshafts are pulled and rebuilt/balanced.

 

[Ronmar]

The driveshafts on these MUST be PERFECT! You throw a shaft on one of these, it typically takes the transfer case with it...