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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Transmissions
Satisfied Customers: 1727
Experience:  16 yrs. experience with auto, manual, & CVT drivelines
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I just put a new 6L80 transmission in my truck new motor

Customer Question

I just put a new 6L80 transmission in my truck new motor also. My PRNDM indicator lights up but the selector doesn't move. It goes into D and R.
JA: Do you have the trouble code? Do you have a code reader or scan tool?
Customer: I do I had a P0602 and a P0700, also a U0121 I believe, I get the messages service trailer brake system and service stabilitrack. I just programmed the ecm and the tcm. The codes are gone after I reset. (In the process of rebuilding the truck)
JA: I'll pass this info along to the Chevy Mechanic so that he can get you a quick fix. What is the model/year of your Chevy?
Customer: 2009 Silverado LTZ 1500 4x4, New wiring harness was also installed, I'm just heading out for an hour or so. email is***@******.***
JA: Are you fixing your Silverado yourself? What have you tried so far?
Customer: Basically it had 280000 miles on it and I had plans to rebuild, it had a 6.0l gas. One Monday after the truck sat for the weekend. I had shift issues and noises coming from the trans, it was fine when I parked it. So I tore into the truck putting in a crate engine and a gm rebuild transmission, with a new gm wiring harness. I used HP Tuners pro to program the ECM to disable the DOD and variable cam the LS3 6.2l I installed doesn't have those, the engine runs great. The trans won't go into fast learn either. I am just waiting for the rear wiring harness, I'll install that then it will likely head to the dealership to see whats up. I know I have ABS/Stabilitrak/Trailer brake system issues, would this cause the trans not to program properly?
JA: Anything else you want the mechanic to know before I connect you?
Customer: Thats about it. The harness isn't here till mid week, if I could be pointed in the place to look I would look. I have the factory manual, but I'm not real keen on the time it would take to trouble shoot the lan networks. But if pointed in a direction I would go into some tests over the weekend.
Submitted: 6 months ago.
Category: Transmissions
Expert:  Chris (aka- Moose) replied 6 months ago.

Welcome, I'm Chris (aka Moose), my normal schedule online is around lunch and after dinner till early morning.

Do all gears work even though the the indicator does not change?

Customer: replied 6 months ago.
I'll take it for a drive today and see. A little more info-the speedo on the dash works but the one through the scan tool does not. What time zone are you in
Customer: replied 6 months ago.
I haven't been able to perform the fast learn procedure also.
Customer: replied 6 months ago.
It won't shift. -service stabilitrak-service traction control- are the messages I'm getting.
Customer: replied 6 months ago.
These are also in my scanner;
C1235 - RR wheel sensor its new
P0010- is not supposed to report
P0454- is a new pump with a switch
P3401- is not supposed to report either. DOD has been disabled, Variable cam had none selected, and errors from them are not supposed to report.
Expert:  Chris (aka- Moose) replied 6 months ago.

Central time.

No transmission codes.

So you select drive, and accelerate up through 1st gear but it does not shift to 2nd?

Does reverse work?

Customer: replied 6 months ago.
Goes in reverse and it works. No shifts, feels like may be in 2nd.
Expert:  Chris (aka- Moose) replied 6 months ago.

Does the computer show the correct gear position when you shift through each gear?

If needed are you planning to overhaul this new transmission?

Customer: replied 6 months ago.
The trans is new from GM. I can't get into the fast learn mode, or see anything from the PCM/ECM
Expert:  Chris (aka- Moose) replied 6 months ago.

Are you saying the PCM shows no signal from the park neutral position switch on a scan tool?

Customer: replied 6 months ago.
but I'm using hp tuners pro, I'm not all that familiar with it.
Expert:  Chris (aka- Moose) replied 6 months ago.

Is that a scan tool or a programmer that makes the truck have more power?

Customer: replied 6 months ago.
It lets you in the program to make changes. I needed to get in to disable the Variable cam and the DOD to get the ls3 to run off the stock ecm.
Customer: replied 6 months ago.
I had a junkyard computer I put in and sync d the vats. Same issue.
Expert:  Chris (aka- Moose) replied 6 months ago.

I do not believe I can figure this one out not in person. Opting out now.

Customer: replied 6 months ago.
K but if I have codes (i do) can the tcm be programmed?
Expert:  Tim's Auto Repair replied 6 months ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you.

does the PRND321 ever not light up?

why did you replace the transmission?

Customer: replied 6 months ago.
It lights up it's the 6spd. The truck had 280000miles on it. And it did the same thing stopped shifting etc. I think it's a limp mode. Anyway figured it was time to replace everything anyway. New trans motor and wiring harness. When the trouble started I went through a field of canola stubble. It hit the harness pretty hard at the brake module, this harness I did not replace. So I just need to know if the service codes are on the dash, that my tuner/scanner can't see would that stop my tcm from being programmed
Customer: replied 6 months ago.
Replaced trans because of milage. Same problem there with new trans. Plan is to replace harness; if that doesn't fix it; take to GM. But I'd like some direction before I take it in
Customer: replied 6 months ago.
I did see the selector move on my scanner, park, reverse, neutral, D6, and D5 manual