ajparry89

Hey Guys, a little puzzled here, hoping someone can help me out. I have an old 2000 express 1500 with the 4.3L for my work van. I have an issue where it does not seem to want to downshift into passing gear. If i manually downshift it into 3rd, it works fine and shifts and gains rpms and picks up speed the way that it should. I have many codes.

P0106 MAP or BARO pressure circuit out of range.
P0108 MAP or BARO pressure signal high;
P0147 O2 heater circuit bank 1 sensor 3;
P0300 misfire (although engine seems to run fine);
P0404 EGR Signal feedback signal out of range;
P0405 EGR Sensor "A" Signal Short/Low;
P1106 MAP Sensor circuit intermittent high;
P0121 TP Sensor or APP Sensor 1 Problem
P0122 TP or APP Sensor 1 Circuit short/Low
P1122 TP Circuit intermittent low voltage

I have replaced all these sensors. yet the codes come back. Because the engine seems to run fine, and I have no complaints other than the downshift issue, I am mostly concerned about fixing that. in my opinion, the only codes here that would effect the downshifting of the transmission are the last TP codes. i figure, the computer doesnt see the throttle opening up, so it doesnt downshift. and infact, the computer is not seeing it open, as far as I know. monitoring it on the scan tool, when I open the throttle, the reading only goes to about .6 volts or so, and the throttle percentage only goes up to 5%. I unplugged the connector, checked 5 volts reference, and good ground. I jumped the 5 volts to the signal wire, and immediately the reading on the data went up to 5v and 100% open. so I put a new sensor in it. didnt change anything. I check to make sure the throttle shaft was spinning when i open it, and it is. I manually turned the sensor by hand (with a small screwdriver) with it removed from the throttle but still plugged in, and the readings only went to .6v Am I missing something else to check? could there be another problem? is there no problem at all with the TP sensor? is it something else causing my transmission not to downshift?

thanks for the help everybody!

ajparry89

I should add another note. I do have an issue of stalling at low speed, like parking lot speed, usually after giving it a little gas, like to pull or back out of a parking spot. Any Idea where I should look next? Thanks for all the help guys!