How to Repair a Chevy Tahoe Z71
What To Do When a 2004 Chevrolet Tahoe Z71 Transmission Won't Shift
Jan 10, 2008
This weekly Q&A session answers your questions about cars and trucks. This week explores a 2004 Chevy Tahoe Z71 that is stuck in first gear.
Question: Chevy Tahoe Transmission
I have a 2004 Chevy Tahoe Z71 with a standard "Hydra-Matic 4-speed electronically controlled automatic transmission with overdrive and Tow/Haul mode." I was at a stop light ,and when I started driving, the transmission would not come out of 1st gear. I took it to the differential shop that had just replaced the differential not more than 3 months back. The shop owner told me it had nothing to do with the differential but he would check the transmission oil to see if there were metal shavings.
He pulled the plug and it was clean. He dropped the pan and found no metal. He said the oil was a little dirty but that was it. He replaced the solenoids and pulled the wire that goes to the computer and manually shifted the transmission and nothing happened. No alarms and no changing of gears even when solenoids where replaced.
At this point he does not know what it might be. I bought the truck 10 months ago. I have not replaced the transmission oil and it currently has 73,000 miles. It is my only car and if you have any ideas of what it might be it would be greatly appreciated.
Answer:
Was the computer checked for codes? A lot of transmission codes will not turn any warning lights on. So the first thing to do is check the PCM and TCM for diagnostic trouble codes.
If that is all fine, then this is probably an internal mechanical problem within the transmission. The 1-2 shift valve, or its spring, inside the valve body may be stuck or broken. You replaced the shift solenoids so it can be assumed, for the moment, that they are good and not stuck.
The 2-4 servo assembly may be damaged or the pressure supply passage to it may be clogged. The 2-4 band assembly may be damaged or worn out, or the band anchor pin broken or not engaging the band.
There is a chance it could also be a software or Transmission Control Module (TCM) problem.
At this point there seems to be no alternative to going to a transmission shop or a Chevy Dealership to have the transmission line pressures tested, software calibration checked and possibly pulling the transmission to do an internal visual inspection.
That's all for this week. Feel free to browse the archives for past topics and other resources. And, as always, if you are stuck and need an immediate answer you can always call Vince on the phone.
