Hello all! I have searched and read through every single post on the web that I could find regarding this p1221 code and I seem to be coming up empty with good answers.

I changed my battery a couple months back and while I was doing it I foolishly left the key in the "on" position and disconnected the battery - shortly after I heard a sizzling sound and my A/C stopped working. [Edit: checked all the appropriate fuses, none have blown, and it worked prior to that event.] That was the start of the problems..

Soon after I started getting "Reduced engine power" PCM - P1221 (only meaningful code) which I know is the 'TPS 1 and 2 performance.' At this point it is so bad that 80% of the time I cannot hit the gas pedal without that coming on and reducing or killing my engine.

Things I've done:

- Charged and measured battery - it checks out.
- Cleaned and regrounded both ground clips behind the headlights, as well as the main negative ground by the battery.
- Inspected wiring from behind the fuel rail through the TPS clip and all looks good
- Wiped down the inside of the TB and verified by hand that it does not stick

I haven't had a multimeter or someone to help out so I haven't been able to check the voltage at the sensor (I don't even know what pins are supposed to do what when.) At this point I'm at a loss and can't even drive it to a shop.. any and all suggestions are appreciated as this is driving me mad.

Might the motor for the TB be going bad? The TP sensor? TAC module? How do I know which? Thanks!

 

Update: so I went and found myself a multimeter and tried testing voltages on the TPS..but no dice. I detected the 5V constant on the plug, but literally no other readings on the the sensor itself or the plug... which tells me I'm most likely doing something wrong but I'm not sure what. Come tomorrow (when I can get my hands on some "safety torx" I'll actually take the sensor off and test it by hand. Also going to open up that access panel and check out the TAC/PCM even though I didn't have any relevant codes.. I had a rodent problem in my car over the winter.

 

Thoughts? Anyone? *bump*

 

What are your other codes?

 

I get 1278 (which is the TCS) but that's it. My car is a 97 and I need to check the TAC version which I'll do today, but no codes directly related to it are being thrown.

On a side note, while I was messing with the TB blade (cleaning) for a while, I managed to take it out for a quick drive and back with no issues. However the problem promptly came back in the morning.

 

For informational purposes in case someone in the future has the same problem.. I can't believe there isn't an easily accessible writeup for this seemingly common problem. Save a lot of headache, and potentially money, and do the following:

1. Attain a digital multimeter
2. Aquire small/medium alligator clips
3. Go to your local auto parts store and buy a set of "safety torx" bits for $3
4. Don't fiddle with testing your TP sensor on the car, just take it off.
5. Attach negative alligator clip to the negative lead of your DMM, and the other end of the clip to the third (of 6) from the top prong inside the TPS
6. Attach the positive alligator clip to the positive lead of your DMM, and the other end to the first clip at the top (as was mounted on the car)
7. Set your DMM to Ohms
8. Ensure you have a starting number between 0-5, and very *VERY* slowly turn the center of the sensor as the TB would - watching that number on your DMM (do it a few times)
9. Reference my explanation below.
10. Now connect the negative clip to post 4, and the positive clip to post 6
11. Repeat steps 7-9.

Explanation:

The sensor is really two sensors, and in this case is represented by the top half of the posts and the bottom half. P1221 is generally caused when these two sensors disagree by a relatively small % for a VERY finite amount of time. If the sensor is working properly you should see the number on the DMM move up and down with full continuity, if the number displayed drops and comes back, even briefly, that is an indicator that there is a problem.

In my case both sensors hit an Open Loop right around 1.9-2.1. Granted this means they technically agreed but there needs to be continuity through the range. Also if I turned too fast (simulating a fast throttle response) it would often lose continuity and OLs would happen there too.

On a side note, the turning mechanism appears to have sediment of sime kind inside (feels sandy) and is likely just in need of a good cleaning.. I'll update with more when I perform sensor surgery.

[adding picture for clearer idea of pin layout if someone IS trying to do it on the car.]

 

Update: I may just have been unlucky, but this is my experience with the sensor replacements.

First attempt: Purchased a Delphi TPS for $50 (great deal right??) and found out that the rotating center of the sensor it turned clockwise - problem with that is the TB post turns counter-clockwise.

Second attempt: Figuring it must be defective, I exchanged for another Delphi - same problem. Lesson learned, despite the fact that it is listed specifically for our cars, either I got 2 defective parts in a row or it clearly is not the correct part despite what it's advertised as.

Third attempt: Found an American Standard TPS for $65, and that one popped right on. Center turns the proper direction, and no more codes! Took the car for several test drives and absolutely no problems so far.


Also, I dug into the original sensor and it appears there was some corrosion happening. How that occurred I have no idea considering the sensor was entirely sealed.