I got a code P0121 "throttle position sensor circuit insuffcient ac"

not sure if it has something to do with the a/c. i just had the compressor removed from the car because it wasnt working and to lose some wait.

anybody know?

thanks

 

I don't think it's an A/C issue via TPS. PO121 is not an A/C code.
To check: Use a volt meter to check reference voltage from the ECM/PCM. Positive probe on gray, negative probe on black. Should see ~ 5 volts. Then, check TPS signal voltage. With TB closed, positive probe on dark blue wire, negative probe on black. Gradually open TB and watch sensor voltage. As you open the blade from closed(idle)seeing 1.2-1.6 volts, to WOT, the voltage values should rise(smoothley)to 4.5-5.0 volts. If not, replace TPS sensor.

Good luck-

 

Check this out this thread from below also....Wrencher may have solved it for ya.

https://ls1tech.com/forums/pcm-diagnostics-tuning/117835-help-ses-light-code-p0121.html

 

I hooked up my A-Tap and it shows .7 volts with it closed and then when i floor it, it goes to 4.6 volts.

anything else to check?

thanks

 

im still getting the P0121 code.
also my TCS light will come on and it wont let me turn it off or on, it just shows off and stays.

also last night, i went to the track and got 2 runs in and both times i would get it off of the line fine, but then it would stay at around 3,000rpms and the car wouldnt move.

is this all related?

PLEASE HELP!

 

Other than what wrencher stated in the thread I linked you to....I dunno Me no pro....just try'n to look at the easy stuff 1st. Did you check the A/C cycle switch? Need some of the puter guru's to give their thoughts. Good luck

 

i see on LS1edit 1.3v that they have a MAP parameters for P0121 and its min is 65 and max 55.
if i change this, is it going to just make the light not come on or is it going to fix my problems also? anybody know??

 

Has anyone ever actually solved this problem or do they just part the car out? That poor guy look how old this thread is! Is this why so many of these damn things get parted out!? Someone who knows all about this issue please make a sticky worthy post about it so the rest of us with little pea brains and anyone who buys one of these cars and tries to modify it can actually have fun with it once they've bolted all of their parts together Sheesh

 

Are you having a similar issue? I don't have all the answers, but I do know that if the voltage is too high, you will not enter the idle routines. I believe that is right at about .7 volts. To reduce this, you have to close the blade with the set screw. If your IAC counts then get too high (say above 100 or more) then you may have to consider porting the IAC or drilling a 1/8" hole in the blade. This typically happens on modified/aftermarket TB's, or even stock ones when there isn't enough airflow at idle (again, modified cars).

There is also a table in the tune under diagnostics to enable the test of this code (at least in later models gen IV's, etc). I don't have my laptop handy to go look right now if there was a table for it in the Gen III's.

You can also simply disable the code if the voltages check out and move on with your life. On a cable TB, this isn't a big deal whatsoever. Like a lot of codes, it's just there to get you to the dealer, and really doesn't have a real effect if the mechanical side checks out. I've done this before, and there are no side effects.

Also, don't forget to reset the sensor. Unplug it, key on for 5 seconds, key off, plug it back in. It will probably throw a code for it, so just clear it and the scanner should report 0.0% or 0.4% TPS. If it's different than this, you have to reset it again.

 

Thank you for the reply doc. Honestly I've been messing with these cars for a long time and I have a friend that helps me tune with hp however I'm not that great at the tuning myself.

I went ahead and drilled my throttle body, I think I have the blade open less than one full turn with the screw flipped now, and that has greatly improved the cars consistency and hot starting already I just can't see how anybody can get away without doing something like this when certain changes are made, I'm so glad I did it.

My setup probably has lower dynamic compression than most street driven setups and so the atmosphere inside the combustion chamber at idle varies a little more during the day with the range of weather that we see than something with stronger static and or cranking compression would and so drilling the throttle body and giving the engine a larger volume of air to work with allows the IAC motor to actually do its job, a job it is desperately needed for and when you have a big cam and a lightweight stall converter it seems the PCM becomes more sensitive to the TPS? I don't know I guess that's all that's left for me to keep breaking lol

The car that I'm having trouble with though with the recurring p0121 also needs its air conditioning recharged, I had emptied it when I replace the engine and I hadn't bothered to recharge it so can that really cause a ghost p0121 code? The car already has its MAP values maxed out because my idle vacuum isn't great because of the low dynamic compression however the air fuel and spark look really good and have been street tuned with a nice wide band, it just needs to idle really high to be stable enough for my liking, I think we are commanding 950 and it only swings around 50-60 RPM each way warmed up so Is it just that certain TPS sensors because of their manufacturing variance can be more sensitive to this issue than others? Or is it the higher than stock idle my setup requires and the lack of pressure in the A/C system Causing me to throw a p0121 no matter what sensor I have? I have no idea why so this is why I'm rambling about it.

So at present the biggest issue I'm having currently is finding quality TPS sensors that last. Or that even work at all Right when they come out of the box, I have two 2002 A4 Camaros, sorry I have no idea what my signature says anymore I only post from my phone, I need to go fix that,.

Currently both have cars have Gen III iron 6.0 engines in front of 4L60E's and both are tuned differently but they both still have stock PCMs LS6 intakes and throttle bodies. The cars are tuned differently because I use one for drag racing and one for SCCA autocross.

TPS sensors typically last me almost a year if I'm lucky and those are the ACDelco brand ones I order from summit or Amazon The part number is 213-912 or the new interchange number is 17123852 these are the only sensors that I have tried that don't almost immediately set an SES light almost always a p0121. These sensors generally fail me when the return spring inside breaks. It causes a myriad of annoying drivability issues . The cheaper sensors usually molded in gray plastic that come from different online retailers or cheap parts stores, I've tried some of them they don't even work at all. It seems to me also the more aggressive the setup the more sensitive it becomes to the TPS being spot on. I've noticed that at present summit lists at least seven different TPS sensors for my application, How do I know which one is the best made?

 

For a mechanical throttle body, so long as the voltage checks out (.4 ish to .65), and the scanner registers 0 to 100%, then the code can be simply turned off for peace of mind. It causes more trouble than it’s worth. I chased a similar issue in the past, and on my own 98 that code is off. These cars are old, and the problem is probably in the harness really, or the PCM, or somewhere else. I have never seen the need for that code since it’s a cable driven TB, unless it’s reporting the wrong percentages. It could also a formula we can’t see in the PCM thinking that “x” value TPS = “x” value airflow, or what not.

This code is only important on DBW TB’s, since if they are not communicating properly, there is a serious safety concern. On those the car does more than just disable lockup on the TCC and so forth, it goes into limp mode too.

As for the AC, that’s not related to the TPS at all.

For reliable sensors, I stick to AC Delco, Bosch, or Delphi. I try to keep to the OEM standard for important sensors. I’ve had that cause issues in the past using cheap replacements.

 

Thank you for the reply doc sorry, I thought I replied earlier I'll mess with it some more this week and let you all know what I come up with

 

Thanks again doc I got a new AC Delco sensor in the mail and I took it out of the plastic package and the little cam inside was tight stiff couldn't turn it at all with my fingers I said eff it and I stuck it on throttle body and I turned it like twisted it forwards like the throttle blade would open it and I felt a clunk I pulled it off and there was no return spring action it was loose just like the other one that I thought was messed up I put it on anyway and cleared the computer and it seemed to work fine it usually takes the while for the code to come on at a hot idle and so I drove over to my friend's house and we turned off p0121. Car seems to be working just fine I'm just not going to worry about this anymore unless it gives me another problem Thanks. I hope this helps anybody having a headache with their transmission jumping up through the gears quickly from a dig limp mode sucks.

 

Total shot in the dark, don't have time to read the thread but I was having this problem and this solved it for me after much tinkering:

https://forum.hptuners.com/showthrea...the-P0121-Code

 

That's Right, that thread should help the majority of folks and that's where I started when I had the problem however as I've come to find if you have a drive by cable set up it is a redundant or superficial code and it can just be turned off if it gives you persistent problems. I think more so than anything what I really gleaned from this is that when dealing with cams in the 230's-240's duration and stock compression ratios The 78mm ls1 throttle body really needs to be modified in some way to allow more base airflow. I just drilled another hole opposite of the one that was already in there (start with a bit slightly smaller than the existing hole and work your way larger if needed) and bingo it was able to close the blade almost completely and get the IAC counts in line and I now have 10° of overlap and your grandma could drive it around the drivability is so good if she had a good set of earmuffs 😉. Course now I'm looking at Camshafts with 16° of overlap or more for my next put together hehe

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You can also the slot the screw holes with a dremel or small drill bit. This allows you to twist the TPS to get volts 5.5 or under. Next reset the TPS.

When slotting the screw holes use the same size drill bit as the screw (don't oversize the slot). Slot just a little at a time. You need to slot both holes. I recall you slot clockwise. Test first by twisting the TPS in the direction that lowers the volts.

Since the slots enlarge the screw holes - you need to make sure you secure the screws tightly so the TPS doesn't rotate backwards if the screws are too loose.

https://www.camaroz28.com/forums/lt1...-450920/page2/

 

LOL holy hell this thread is ancient! This was figured out back in 2003 when people got their hands on LS1edit, the P0121 min/max error tables with aftermarket cams that don't have as much vacuum as a stock cam does so the range was off for the test.

 

Thanks for diving in, Yes as far as I understand it LS1 Edit has More detailed tables regarding the TPS that can solve the p0121 issue without turning the code off however HP tuners does not offer the same level of tunability there and I don't have access to LS1 edit at the moment

 

It seems to me the only reason to do this would be because you have a throttle blade so far open with the set screw to get the base airflow in check, however as I have discovered and most others have two having the blade cracked open that far is not consistent enough for the IAC to keep up with because the throttle body expands and contracts with heat as the engine warms up and cools as you drive it. If you drill another small hole in the throttle body blade to allow more air in you can then close it all the way like stock and then you don't have to modify the TPS sensor to keep the volts in check It's permanent and it allows the IAC to compensate for environmental factors better and you don't have to worry about it coming loose.

 

There is a table under diagnostics to disable or modify the p121 test, however basically you’re doing the same thing as disabling the code. I will say though, that’s probably the more appropriate way to kill the code, and leave the sensor code enabled so it will tell you if the sensor itself fails. When I initially responded to this thread I didn’t have my laptop on me to verify the Gen III’s had that table, but they do. I just couldn’t remember and I didn’t want to give false information. That table is on the same page as the MAF test, ie where you would go to disable the MAF.

Either way, it’s not a big deal on cable throttle bodies. TPS really only controls trans and PE triggers, and if it’s faulty it’s not gonna go psycho and floorboard the blade for you if there’s a sensor issue like on a DBW TB. Huge difference there. So long as it reports properly for 0 and 100 and everything between, that’s all that sensor needs to do to be effective and serve its purpose. The only caveat is the idle routines, and making sure you don’t have to much voltage for full closed. Iirc, it’s 0.7 v. I may be wrong about that number, but it shouldn’t be too high otherwise it won’t go into idle routines.