Got my transmission rebuilt not too long ago and ever since I have been randomly throwing a p0121 code. I have noticed that when I try to accelerate sometimes it feels like it just bogs down and will accelerate but very slowly and my rpm's stay around 2000 even at wot, but if I shift into neutral it will rev up normally, then if I go back into drive it bogs down again. Again this happens randomly sometimes it will happen when my SES light is on and other times my SES light will be on and I can accelerate normally. Also could it have been possible for them to erase my engine tune when they re-tuned the transmission? My truck is cammed so I think it is throwing the code because the map sensor is reading the pressure in the intake and it is out of it allowed parameters. However the SES light never came on before going to the shop and the tune that was on it before took care of the p0121 problem. So I am wondering if maybe they erased that tune and if I got another custom tune would take care of my acceleration problems?

 

It isn't downshifting, so you're in the wrong gear. Which trans do you have?

 

Take a look at this page I believe it might help you. http://www.obd-codes.com/p0121

 

It is a 4l60-e and I have looked at that page and tested my tps and it all checks out.

 

Well you certainly could have the tune looked at by your tuner. However if this thing is doing this intermittently then I would not rule out the info on the page I linked. The thing here is you need to monitor the TPS and the other info on that page while it throws the code and is not working the way it should. I'm sure something will not look normal when the condition happens. Just because the TPS checked good do you monitor its operation when the condition happens? Also how did you check out the TPS?

 

Well I have been monitoring the voltage at the tps well the truck works normal and when it is not down shifting and it has been working properly during both situations. So I am pretty sure the tps is working fine and that is not the problem.