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We got this 03 Chevy K2500HD pk tk with a diesel engine and the Allison automatic trans. Got 134,000 on the clock. Came in with the complaint that when vehicle is in limp home mode. Also the display for the trans range on the dash was dark. Diagnosis confirmed multiple codes in the TCM. The only forward gear it had was 4th, at least that is what the scan tool showed, and trying to drive it was like taking off in high gear. PNP switch on side of trans was broken so we replaced that. Only code that reoccurs now is a PO872 (Shift Solenoid E Error). Further diagnosis led to stuck valve corresponding to pressure sensor E. Testing proved shift solenoids are all working. We took them all down and bench tested them. We replaced the shift valve and code PO872 still reoccurs as does only 4th gear forward. Reverse works fine, as does neutral. No other issues with truck. Obviously we are missing something. Help!!!! Customer wants his ride back.

i've had to reburn the pcm's on these for all sorts of issues. 4th gear is the go to gear for limp in this truck. if you can shift the tranny through the scanner then the pcm being reprogrammed should solve this.

Ignition switches were a problem on these I think. Make sure powers and grounds are all good.

Sonnax makes a tool to resize the valvebody bore. You will also get that code if it is low on fluid.

wbuxton wrote:Sonnax makes a tool to resize the valvebody bore. You will also get that code if it is low on fluid.

Does that indicate that they had an issue with the bores getting tight?

I know the guys have the tool and have to hammer it in, let me check with them and I'll get right back...

Thats correct, the resizing tool you can get from transtar or axiom. If they are not local check with sonnax.com

We have had great results.

We did it again! - again. Fixed it. The problem turned out to be a stuck shift valve in the one valve body. We took the valv body down and examined each valve and found that one was stuck for whatever reason. Took it out, took 400grit emery cloth to it a little, cleaned it lubed it good, stuck all back together and presto, it works just fine.

Good job! We see a couple a month with this problem. Why? I'm not that smart....

Well, it may have something to do with service interval. This one, the trans had never had filters or fluid change.