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02 Sierra 2500hd p1221 code

I love my Chevy Chevette!
Posts: 1
Joined: 01/14
Posted: 01/07/14 03:55 PM

Good evening.  I have a 2500hd with an 8.1 l w an Allison.  I cracked my TPS while working on the alternator. It coded immediately with p1221 and a few others.  I replaced the TPS and it seemed to have worked initially.  When it sits and cools it codes again at start up. I erase codes and eventually I can get it to run.  I thought I had a faulty (new) TPS, so I replaced it again.  It has failed again. It flashes reduced engine power and won't go over 15 mph.  What changed?  My initial repair had nothing to do with this. I only replaced it because I broke the original.  Idk... Frustrated.  

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V-6 Camaros rule!
Posts: 36
Joined: 10/13
Posted: 01/07/14 08:16 PM


P1221 - GM Type Powertrain - Manufacturer Controlled DTC - Manufacturer Controlled

TP Sensor 1-2 Correlation Conditions

DTC P0606, P1517 and P1518 not set, key in crank or run mode, system voltage over 5.23v, Electronic Throttle Control serial data present and the PCM detected the TP Sensor (2) signal disagreed with the TP Sensor (1) by more than 75% for less than 1 second

i would almost bet that when the tps got broken.. it broke where the connector plugs in..   if so ..

then either look down into the connector to view the terminals that they are not deformed by the impact.  the replacement is a delco Part Number:  PT787 pigtail.

you may want to examine the live data with a scan tool...

there are actually 2 throttle position sensors.. one that starts at less than 1 volt.. usually around 0.70 and goes up to about 4.5 volts

the other starts at 4.5 volts and drops as you open the throttle..

both of these have individual ground connections.. at the computer...

this is the section for the throttle body...

81L TAC Motor TP Sensor 2002 Zpsea9753db

see the six wires into the TPS sensor lower right of the above image..

81Laccelerator Pedal Position Sensor 2002 Zps8a5710c7

look at all the wires to the accelerator position sensor .. thats on the throttle pedal assembly...

what was the original repair????  did all the ground wires from the fuel injection harness get hooked back up tightly..  if there is a bad ground and it will take a me a bunch of hours to go page by page thru the wiring diagrams to attempt to figure it out.. cooling off and setting a code is probably a terminal in the connector issue..

and do you have an advanced scan tool.. where you can see the data stream???
as far as i recall off the top of my head.. the TPS1 and TPS2.. the APS1 and aps2 sensors.. all sweep in differernt directions..  

Obd2scandatachart Zps65411833

Obd2scandatachart2 Zps6e93e7de  

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