P0121 Code Help???
Thread Starter
Teching In
Joined: Aug 2010
Posts: 12
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P0121 Code Help??? My CEL light came on and I went to autozone got it scanned. Came up with P0121, Throttle position sensor. I had the GXP in the shop and they checked every single sensor according to procedure. MY mechanic told me he tested over 10 different sensors and veverything checked out ok. He said I would either need to take it to GM or star with cleaning the throttle body out.
Before I go broke goiing to GM I really would like to know if anyone has had this problem or could provide some guidance. I have a K&N on there as well if that makes a difference.
Thanks
Before I go broke goiing to GM I really would like to know if anyone has had this problem or could provide some guidance. I have a K&N on there as well if that makes a difference.
Thanks
Remove the K&N before going to the dealer. If the dealer wanted to be a stickler, they could deny warranty coverage, and you'd have a tough time fighting it. They could argue that the oil from the K&N CAI caused the failure, since the TB is connected to the intake via the MAF. Now, we all know this is bullshit, but they would at least have an argument.
Save yourself the headache and make the car as stock-looking as possible before taking it in.
Save yourself the headache and make the car as stock-looking as possible before taking it in.
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TECH Fanatic
Joined: Jun 2007
Posts: 1,316
Likes: 3
From: Dolla$ , TX
My CEL light came on and I went to autozone got it scanned. Came up with P0121, Throttle position sensor. I had the GXP in the shop and they checked every single sensor according to procedure. MY mechanic told me he tested over 10 different sensors and veverything checked out ok. He said I would either need to take it to GM or star with cleaning the throttle body out.
Before I go broke goiing to GM I really would like to know if anyone has had this problem or could provide some guidance. I have a K&N on there as well if that makes a difference.
Thanks
Before I go broke goiing to GM I really would like to know if anyone has had this problem or could provide some guidance. I have a K&N on there as well if that makes a difference.
Thanks
So with that said, if you clear the code and it does not return then its an intermittent issue. With that said, you need to hook up an oscilliscope to sensor signal wire for the throttle posistion sensors, and the throttle sensors, and slowly go through the range on each one and watch for "glitches" and "Drop outs", and also move around any wiring. According to the service manaul, this code is specific to the throttle body and not the pedal, despite the generic code listing. So you can likely skip testing the pedal.
You can do the "Service manual way", which is not my ideal way of testing these issues, but its a good place to start. Which ive attached below.
TECH Fanatic
Joined: Jun 2007
Posts: 1,316
Likes: 3
From: Dolla$ , TX
CONDITIONS FOR RUNNING THE DTC
DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0335, P0336 are not set.
The engine speed is more than 450 RPM .
The engine coolant temperature (ECT) is between 70-125°C (158-257°F) .
The intake air temperature (IAT) is between -7°C and +125°C (+19°F and +257°F) .
DTC P0121 runs continuously when the above conditions are met.
CONDITIONS FOR SETTING THE DTC
The TP sensor 1 disagrees more than 9 percent from TP sensor 2.
The TP sensor 1 disagrees more than 9 percent from the predicted value.
The above conditions are met for less than 1 second .
DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0335, P0336 are not set.
The engine speed is more than 450 RPM .
The engine coolant temperature (ECT) is between 70-125°C (158-257°F) .
The intake air temperature (IAT) is between -7°C and +125°C (+19°F and +257°F) .
DTC P0121 runs continuously when the above conditions are met.
CONDITIONS FOR SETTING THE DTC
The TP sensor 1 disagrees more than 9 percent from TP sensor 2.
The TP sensor 1 disagrees more than 9 percent from the predicted value.
The above conditions are met for less than 1 second .
Staging Lane
Joined: Jul 2009
Posts: 72
Likes: 0
After some investigating I learned P0121 was due to the computer figured out a variance in intake air speed. This made me believe this could be caused by a dirty mass air flow sensor. So I bought cleaner for the MAF and the throttle body and cleaned them.
The MAF I removed and sprayed, the throttle body I cleaned in place with a rag I sprayed cleaner on to wipe down the inside on the blade and where it seats.
The check engine light went out shortly after and has been out for a day so far.
The MAF I removed and sprayed, the throttle body I cleaned in place with a rag I sprayed cleaner on to wipe down the inside on the blade and where it seats.
The check engine light went out shortly after and has been out for a day so far.
TECH Fanatic
Joined: Jun 2007
Posts: 1,316
Likes: 3
From: Dolla$ , TX
After some investigating I learned P0121 was due to the computer figured out a variance in intake air speed. This made me believe this could be caused by a dirty mass air flow sensor. So I bought cleaner for the MAF and the throttle body and cleaned them.
The MAF I removed and sprayed, the throttle body I cleaned in place with a rag I sprayed cleaner on to wipe down the inside on the blade and where it seats.
The check engine light went out shortly after and has been out for a day so far.
The MAF I removed and sprayed, the throttle body I cleaned in place with a rag I sprayed cleaner on to wipe down the inside on the blade and where it seats.
The check engine light went out shortly after and has been out for a day so far.
Cleaning the MAF will not resolve a P0121... only a variance in the 2 throttle sensors will create the code P0121......
TECH Fanatic
Joined: Jun 2007
Posts: 1,316
Likes: 3
From: Dolla$ , TX
I got this thread mixed up with another thread I'm helping someone with,
It is possible for the MAF to read incorrectly and cause the predicted value to be incorrect and not match the actual position of the throttle body.
What g/s is the MAF reading at idle and at 3000 RPM's ? Also, what is your fuel trims at idle and at 3000RPMS.
It is possible for the MAF to read incorrectly and cause the predicted value to be incorrect and not match the actual position of the throttle body.
What g/s is the MAF reading at idle and at 3000 RPM's ? Also, what is your fuel trims at idle and at 3000RPMS.
