I just bought a used '05 Z71 4x4 with 5.3 Vortec engine and 55,000 miles. Two months into ownership, the transmission went out losing OD & 3rd gear. (By the way, I knew the previous owner and know for certain that he did not do any towing with this truck or anything that would be considered extraordinarily abusive to a transmission).

Anyway, I had the transmission rebuilt and picked it up from the garage to take home and all of a sudden the truck is now throwing the P0171, P0300, and P0131 PCM codes. Previous to that, the truck had not given me any code problems.

I took it back to the tranny shop immediately. They put it on their diagnostic machine and could find no problems with the O2 sensor circuits or with the fuel system, they also could find no vacuum leaks and informed me that on the 4L60E transmissions there are no vacuum lines that could be left unhooked or leaking. They reset the code and told me to drive it for a few days to see if it occurs again.

Conditions on the day I picked up the truck were -30° temp and the truck had been sitting in their heated shop for several days. I'm suspecting maybe some condensation built up and froze on the O2 sensors? But one would think that it had thawed and dried by now.

It is now about eight days later with no reoccurences of the codes until today when the outside temp is around 30°. The truck started to idle very rough with RPM's dropping to around 400.

This weekend, I plan on using some MAF cleaner, and checking for vacuum leaks, are there any other suggestions?

I'm usually a Ford man but went against my better judgement when I bought this truck. Have had it for three months and have already had to sink $2000 in repairs and it seems to be climbing! Not good.

 

the P0300 code would cause your rough idle because you might not be running on all cylinders. Try changing sparks plugs and see what that does

 

If it does not happen again I would not worry about it.

 

Well, this weekend I pulled the MAF sensor and sprayed some cleaner on it. So far, the codes have not reappeared and the truck is running fine. I took it out for a fairly long highway run and all seeme fine. Keeping my fingers crossed.

 

Plugs for that motor are $13 each and very unlikely to be the cause of any problem at 55k miles. Dont just start throwing parts at it. That is not the way to fix anything.

P0300 is random missfire - code IS CAUSED by the rough idle because of another problem.
P0131 BANK 1 SENSOR CIRCUIT LOW VOLTS
P0171 Fuel Trim System Lean Bank 1

That leads me to belive you possibly just have a dead O2 sensor.(i belive that would be the drivers side o2 closest to the manifold) Does the rough idle seem to be rich? or has the gas milage gone down dramatically since you got it back?
-30* temps i could see the possibility of an o2 sensor heater dying on one of that age. being that its a LOW volt code, not and open circuit code - if you have a friend with a scanner that wont charge you $200 to read the streaming data and see what the 02's output voltage is to the ECU, then test the output lead with a volt meter to verify a bad sensor. They could have pinched a wire unknowingly replacing the trans but it cant be visably seen. Ive seen wires get cut without tearing the casing and one strand left conducting the power.

If it doesnt come back just figure it was a dirty MAF, ive had to clean mine at 54k miles.

 

its possible they left some of the connections off of the transmission after the rebuild ( this happen to me when I had my 97 Tahoe tranny rebuilt) they left some electrical connections off and as soon I started to drive it off the lot it started setting all kinds of codes....
they took it in read the codes climbed under the truck did something cleared the codes and they never came back....