I am having a hard time tracking down this issue. I have been replacing TPS sensors for years on this car. I have also replaced the TPS pigtail, but I still get the TPS high voltage code.

Whats funny Is that the car will be idling, then it will almost die, then throw the code.

I was able to Map the TPS with autotap & verify that there are no hiccups. I also reset the code lastnight. After starting the car this morning, it ran for a minute, then surged to a very low RMP, and threw the code once again.

Any ideas? I have suspisions that I may have a wiring harness issue somewhere..

-Adam

 

What kind of tb? Slot the tps and set it where you want.

 

when I installed my Holley tb I got the TPS low voltage code after a stumble and die.
Needed to elongate the TPS mounting holes and rotate to achieve adequate voltage.
Idle should be above .20, below .90 volts - otherwise it throws the codes.
Stock mine was .67 volts at idle so I set mine there. Also worth checking is WOT voltage - should not exceed 4.9
I was told these specs from another member here - seemed to work.

 

Thanks for the replies. It is a stock throttle body.

I can see where a low voltage code would cause this issue at idle, but how would it be that i am getting TPS HIGH at idle? That doesn't make any sense to me at all..

I guess this would indicate that my initial voltage is over .90...

Now my only problem is how to verify the voltage at idle? I have autotap, but this only shows TPS percentage, not voltage... unless there is a way to check this with autotap that I am not aware of?

-Adam

 

how often does the code appear?
what happens after you changed sensors? how long in between codes?

I was told position % is reallative to the idle voltage the car lears at first start.
If you start with .50 volts , no throttle - it baselines that as 0 % open and will allow a 4 volt gain within the opening sweep. So 100% = 4.5 volts
It's not exact though - mine reads 100% open before the exact 4 volts is added to my idle reading.

So, why your car is thinking idle has over .90 volts is pretty strange since it's stock.

I have a mechanic with a scan tool - I have no clue how to read volts - maybe a local Autozone or someone can read it for you...

 

Oddly enough, the code appeared immediately after i replaced it this time. I cleared the code, and the next morning it kicked off the code again.

I have been chasing this for years...

I am going to do some searches & determine how to verify the voltage & see if I might need to slot the TPS to adjust it properly. Only thing I can think of..

-Adam

 

Try checking all of your engine to chassis grounds. I was having a reoccuring (sp?) TPS problems that wouldn't go away even after I replaced the sensor. After checking the wires (which were good) I then disconnected all the engine to chassis grounds and cleaned all the contact points. No problems after that.

 

95firehawk,
Great idea. I will do that & see how it goes.

Thanks

-Adam

 

According too the diagnostic tables on the GM service website, the "TPS High" code (P0123) sets when the TPS voltage exceeds 4.9 volts. Condition must last for at least 1.0 seconds. If the sensor has been changed and the pigtail has been changed, that would appear to indicate in intermittent short in the wires between the reference voltage wire and the signal wire. Have you checked the connections at the PCM connector?

 

Thanks for the reply Ijuneer,

Heres what I have done. I was working on this tonight & I am sitting in my car looking at Autotap right now. I was able to determine how to view TPS voltage, so far it looks good.

Earlier tonight I reset the code, started the car, and the code came back. I decided to go ahead & slot the TPS to eliminate the possibility of having high voltage to begin with, over .90 volts. No change. it sits at .40 baseline now.

Based on what you have just suggested, I agree that there seems to be some sort of intermittant short. For this to be occuring at Idle, a short sounds like the likely culprit.

The car has been almost cutting out on me at cruising speeds, and I bet it has something to do with this short, or a voltage surge coming from somewhere.

I will try & take a look at the connector area tomorrow evening after work. I will unwrap the trunk of wires & trace it all the way back to see if I can track anything down.

I am starting to think, based on my history of these types of issues with this car, that I may be in need of a wiring harness swap? Damn thing is $1000 from Jason Cromer..

-Adam

 

One more thing that I have noticed, and i do not think this is normal.

My fans are staying on for a period of 45 seconds or so after I shutoff the car. I do not think this is normal behavior. This started occuring after i had the PCM programmed by PCMforless.

Does this behavior indicate something i should be picking up on? Possibly bad PCM, Corrupt tune... Etc?

-Adam

 

I'd ask PCMforless about that - might be intentional?

A short will be a bear to find - good luck with it.

 

Before I'd go replacing anything I would try a couple of things first. Did you check your grounds yet? If not it wouldn't hurt to make sure that the contacts are nice and clean. Next I would get a multimeter and check for continuity between the pin at the sensor and the pin at the PCM like Injuneer said. If that turns out to be the problem then I would just replace the 1-3 bad wires. It would be a lot cheaper to cut the wire about 2 inches in from each side and solder in new ones. Then you can run the new wires inside the conduit and noone will be able to tell the difference. This is all pending that the pins themselves are good. Keep us updated.

 

95firehawk,
I was able to clean the ground on the passanger side fenderwell, The ground from the battery Is attached there, as well as the PCm ground I believe?

I only see 1 other ground. This comes from one of the bolts holding the ICM in place & goes to the Drivers side lower fender well. I have not cleaned this one yet. Headers were too hot to get in there when I had time to work on it yesterday.

Are there more grounds somewhere? Did I foget to put a ground back in place when I pulled the motor years back?

How many total grounds are there, and where are they located..

-Adam

 

I finally found the root cause of this issue today.

There is a 3 way connection where the TPS & PCM temp guage share a ground wire. The connection a the 3 way was bad. We were abkle to trace this by checking continuity between the #6 Pin on the BLACK PCM connection and the other end of the wire at the TPS pigtail. Once we cut the 3 way connector out & respliced, everything came back to life!!

I have been chasing this issue for over 5 years now.

Thanks to everyone to made suggestions on this thread. I had everything printed out & laying in front of me while I used tech info from Shoebox's website to locate the appropriate pins.

Special thanks to Injuneer for his guidance & to Shoebox for his awesome website!

-Adam