Ok so ive been getting a p1221 code. I got a 02 envoy and its slow to crank at times (mostly when cold but sometimes when hot) and bogs down a little every once in a while when you hit the gas but not always. Just replaced the TB and still getting symptoms but the code hasnt popped up yet since the system hasnt cycled. Any ideas? I know the fan clutch can throw the code but i wouldnt think itd have the symptoms. It also goes into limp mode every once in a while but shutting off and back on fixes it. also i took a test light to the connector and only two of the eight prongs lit up. not sure if thats normal or not but i thought id include it
p1221 and tps issues
- Thread starter InsaneOctane
- Start date
Mounce
Member
Slow cranking is a battery issue, how old is your battery?
Did you reset the pcm when you replaced the throttle body? The pcm learns a tune overtime as the throttle body gets dirty and adjusts the tune to deal with the dirty throttle body. If you clean the TB (or replace it) without resetting the pcm, or reset the pcm without cleaning it, you'll normally experience stalling.
Did you reset the pcm when you replaced the throttle body? The pcm learns a tune overtime as the throttle body gets dirty and adjusts the tune to deal with the dirty throttle body. If you clean the TB (or replace it) without resetting the pcm, or reset the pcm without cleaning it, you'll normally experience stalling.
I disconnected the battery for a few min thats it. The battery is 7 months old.
Slow to start. Id have to go back and look at maint records i juat bought the car off my grandmother for my wife and she gave me a huge stack of all the maint done since she bought it new.
Slow to start. Id have to go back and look at maint records i juat bought the car off my grandmother for my wife and she gave me a huge stack of all the maint done since she bought it new.
Tiggerr
Member
Ok so I've disconnected the battery and reconnected and have the same issues. I drove 200 miles yesterday to visit family and no SES lights popped up. So I'm back to square one. Maybe a pedal position sensor? I just replaced the fuel filter just in case as well.
gmcman
Member
- Dec 12, 2011
- 4,656
Double check the TB harness, use some electronics cleaner on the terminals, make sure all the pins are in their proper position.
Pull fuses 10 & 28 for about 10 min.
Turn key to ON with all the dash lights on. DO NOT START AND DO NOT TOUCH GAS PEDAL. TB will perform series of noises during this time.
Leave key ON for about 5 minutes. DO NOT turn key off. DO NOT turn key off for the duration of the relearn
Start engine, DO NOT TOUCH GAS PEDAL, let idle for about 8-10 min.
Once engine has fully warmed, idle should settle around 600-625RPM. Generally under 650 RPM.
Pull fuses 10 & 28 for about 10 min.
Turn key to ON with all the dash lights on. DO NOT START AND DO NOT TOUCH GAS PEDAL. TB will perform series of noises during this time.
Leave key ON for about 5 minutes. DO NOT turn key off. DO NOT turn key off for the duration of the relearn
Start engine, DO NOT TOUCH GAS PEDAL, let idle for about 8-10 min.
Once engine has fully warmed, idle should settle around 600-625RPM. Generally under 650 RPM.
Ok I'm trying that now. Earlier looking at real time info with the pedal to the floor the tps was reading at 30%. I just hooked a volt meter to the pins on the wiring harness plug and all but one were at .003V the other was at .780V or so with the switch on and engine off. Measured resistance as well. 6 pins were at between 2 and 15 olms the remaining 2 were at 0.
gmcman
Member
- Dec 12, 2011
- 4,656
Just a FYI, don't use a 12V test light unless you know you are testing a 12V circuit. The PCM for the most part works off a 5V reference and the 12V test light could easily overload the circuit.
Just finished. Still shows symptoms. Throttle still reads at 30% with the pedal all the way down.
gmcman
Member
- Dec 12, 2011
- 4,656
Can you look into the intake tube at the butterfly and see if it opens with someone pushing on the accel pedal? Do you know if anyone may have pushed on the butterfly with it energized? If there's any conflict with the pedal angle and the TB it will go into limp mode for safety.
I believe there's a 5V reference shared with the clutch fan control, I'm not well versed on the schematic though but it sounds like your issue may not lie with that fan reference.
I believe there's a 5V reference shared with the clutch fan control, I'm not well versed on the schematic though but it sounds like your issue may not lie with that fan reference.
Tiggerr
Member
I just did an ohm resistance test on the pedal position sensor. Resistance is off so I'm gonna guess this is where my problem lies.
It hasn't gone back into limp mode and the relearn took because it runs a little better now but not a whole lot.
It hasn't gone back into limp mode and the relearn took because it runs a little better now but not a whole lot.
gmcman
Member
- Dec 12, 2011
- 4,656
The pedal and TB work together, one will increase as the other decreases, not sure if it's ohms or volts but they communicate with each other and if one is out of whack you get the REP.
Could very well be the TB since the code is a throttle position sensor code. This is where the Roadie needs to chime in, he understands this circuit in depth.
Is there a dead spot when you work the accel pedal?
Could very well be the TB since the code is a throttle position sensor code. This is where the Roadie needs to chime in, he understands this circuit in depth.
Is there a dead spot when you work the accel pedal?
Tiggerr
Member
I did replace the TB already. The accelerator bogs when I initially pressed but it's not every time.
gmcman
Member
- Dec 12, 2011
- 4,656
Copy...I forgot.Tiggerr said:
I did some research and if I'm not mistaken, the 5V reference should be the light blue/black wire and the purple should be the signal for the PCM. When you press on the accel pedal, key on, engine off, the purple wire should increase from about 1-1.5V to around 4.5V.
If you have 5V on the light blue/black wire then the fan clutch should be good.
Have someone press on the accel pedal and move the wires around and see if the butterfly behaves differently.
Are those the wires on the TPS that you're referring to? Also, is there a resistance test for the TPS? I've found one for the APP but not for the TPS.
Mooseman
Moderator
Try this, disconnect the fan clutch connector. It runs off the same 5V reference as the TB and there have been instances in the past where a defective fan clutch affected the TB. You will get a CEL and code for the fan but you can still drive it for a while. Just avoid hot temperatures and the A/C.
The purple wire jumps around from 4.1-4.5V regardless of pedal position. Light blue/black wire is at 5V
gmcman
Member
- Dec 12, 2011
- 4,656
If your butterfly moves smoothly and this has happened on 2 TB's, it's looking more like a bad pedal or a gunked up contact on the TB. Under the plastic cap are the wiper contacts but I'm thinking a wiring issue or more likely a gas pedal.
There are other tests to confirm good wiring, especially from the fan clutch and PCM.
How long after you installed this TB did you start having these problems?
There are other tests to confirm good wiring, especially from the fan clutch and PCM.
How long after you installed this TB did you start having these problems?
The problems existed with the original TB. Then I replaced it and it had the same problems. I actually put a new pedal on it yesterday and the same issues are showing up. I'm beginning to think there may be an issue in the harness.
The butterfly on the TB moves smoothly. I manually opened the throttle to 100% and it read correctly. So something going to the throttle body is only telling the TB to open to 30%. Is there a test for the APP sensor to tell if it's good or bad? If it's not the APP sensor I'm completely lost. I've chased every wire and all are intact.
I got a Dorman pedal to replace it. I'll see if I can find somewhere that has the GM one in stock. Probably a dealership. I checked resistances and the APP varies from .5 ohm to 3.35 ohms depending on the position. I remembered reading something about a resistance check and if I remember it was supposed to range from .5-5 ohms.
gmcman
Member
- Dec 12, 2011
- 4,656
I don't have the service manual handy until I get home, hopefully some one will jump in before then.. But fuse #23 is the ETC fuse, check that.
With someone holding the gas pedal to the floor, look into the TB and wiggle the wires at the fan, TB, PCM, and see if you notice an changes in the butterfly opening.
With someone holding the gas pedal to the floor, look into the TB and wiggle the wires at the fan, TB, PCM, and see if you notice an changes in the butterfly opening.
Mooseman
Moderator
A faulty PCM should throw a code but its happened in the past that it doesn't. Easy enough to replace it. Just do a security relearn. If it is the PCM, it will eventually need a CASE relearn to get rid of the CEL.
I'm just at a loss as to what it could be. The TB and APP sensor are both brand new. All the wires and connectors are intact and have been putting out good voltages so far. The PCM is the only thing I can think of between the APP and the TPS that would tell the throttle to only open to 30% with the pedal to the floor.
Mooseman
Moderator
If you have a pick-a-part nearby, you could get a PCM from the same year cheap. These PCMs are not known for failing a lot so one from a junker should be good.
