U2106

[Somis Duramax]

I finally got around to my gauge install. Got a copy of "Got Gauges" and started. Gauge pod was drilled in the wrong spot for the speaker and Autometer is working on the problem. Ran the boost line and tapped the light wiring to the INTPARK fuse in the engine compartment. None of the wiring is hooked up because the pod doesn't fit. Anyway after restarting the truck the SES light was on so I downloaded the faults:U2106 Throttle Actuator. Cleared fault,keeps coming back. Rechecked all wiring etc. no joy. Then also noticed that there is no underscore under the PRND21L indicator and it goes into gear with a horrific clunk. Removed The Juice, cleared code still no good. Any of you great wizards have any ideas? By the way truck is a 2003 C3500

[mdrag]

Somis,

Here is a link for OBDII codes:

www.obdii.com

General Motors U2106 Lost Communications with Transmission Control System

I would check the connectors to the NSBU (neutral start backup) switch to make sure they are secure. The NSBU switch is mounted on the driver's side of the Allison. If you click one of the links in my sig, there is an album with pics of the NSBU switch.

If the connectors are secure, you MAY have a bad NSBU. I replaced mine as a preventative measure since the BLACK old style NSBU switch has known issues, and the new TAN switch is an improved version. The part# for the new switch is clearly displayed in the pictures and was about $54 at my local Allison dealer.

I'm going to move this topic to the 2500HD/3500 HD Trucks & Drivetrain forum, since your problem MAY be more appropriate for that forum (drivetrain related). Good luck.

[mdrag]

Somis,

Check the (2) connectors to the TCM also. The TCM is located under the hood. Go to:

www.kennedydiesel.com

Choose the TECH TIPS, then DURAMAX TIPS, and then the link to the HIGH IDLE or OVERDRIVE LOCKOUT instructions. There are a picture or two showing the locations of the TCM and ECM.

mdrag

[Trippin]

Somis,
I'm a newbie just turned contributor, but my first thought would be to check all the fuses. Perhaps one blew during the install. Simple stuff first. :D
Good luck! Keep us informed.

[ 01-03-2003: Message edited by: Trippin ]</p>

[Somis Duramax]

Mdrag,This has the black switch in it. Connectors are good as are pcm connectors.

Trippin, fuses are good, so, off to the dealer. I will keep ya posted. Thanks for the help.

[SteveO]

SoomisDuramax,

You have a blown fuse or you have pulled a Fuse/wire out enough it's not making contact or cut a wire..

Your symptoms sound like the TCM (Allison Trans Computer) is not powering up.. Please Check (with a test light) "IGN 0" fuse and wiring which is located in the side panel at Drivers door..

Hope you get it fixed..

[ 01-04-2003: Message edited by: SteveO ]</p>

[Somis Duramax]

This is the latest: Called dealer to see if service dept.is open, went out started truck,the underscore on shift indicator was back and SES light was on.Plugged in scanner cleared light no more problems. Drove for 40 miles put juice back in, still works fine. I think SteveO might have hit it I did have that fuse out but used IGN3 for 12v to pyro. Does this truck require several starts to clear pending codes? Need to also contact Autoxray as my scanner w/2003 software says u2106 is Throttle Actuator. Now if Helm would just print the manuals. Thank you all for the help.
Tim

[SteveO]

Somis Duramax,

"Does this truck require several starts to clear pending codes?"

Yes, The control module turns OFF the "Service Engine Soon" Light after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

The reason I said it was a fuse/wiring problem was
1: You said it had a U2106 which I knew was a Comunications problem.
2: You said the PRND2l was not under underlined..
3: You said the transmission had a Horrrible clunk into gear..

They all point to the TCM not powering up..
If the TCM is not powering up, there is no way for the PRND2L to know what gear it's placed in.
The Horrible Clunk was the transmission going into 3rd gear because without power (to the TCM) the trans will become a none Electronic trans and will resort to 3rd gear or commonly known as "Limp Home Mode...

[mdrag]

SteveO,

You da man!! Thanks for the correct diagnosis and thorough explanation.

mdrag