Can someone explane what/why I need to replace a TPS on a 97

[happydog500]

I have a 1997 Lesabre. One day it started running rugh and I got a "Check engin" light. I went to Autozone and the code said, Throutle posisition sensor.

The next day it ran OK. Not perfect like it did, but pretty good. The guy at auto zone looked at the autozone website and he said all I had to do was unscrew the to screws and upplug. Screw back in and plug in and I'm set. I looked in my book and it said I had to take to the dealer or a macanic to "program" it or something like that. (program might not be the word, but something like that).

The part is a very simple thing. All it has in it is a spring wraped around a round piece with a tab.

Which one is right? Just put it in and I'm readdy to go? Something tells me it's not that easy.

The book said when the car gets a TPS code, it will "reset" the TPS. Can someone explane what it did when it, "reset" itself after a code? What and why do I have to do something after I put in a new one? Thanks, Chris.

[HotZ28]

Most of the newer car equipped with TPS, are not adjustable per say, however, when you do replace a TPS, you need to check the TPS for proper voltage. They can move slightly on the mounting screws. A slight movement can vary voltage!

The TPS is simply a potentiometer used to vary voltage. The best way to check the voltage is with a scanner, but if you do not have access to one, you can use a DVM. The TPS WHITE wire, is the PCM reference signal and should measure 5.0V with ignition on. (Engine does not need to be running) The BLUE wire will show variable voltage from a closed TB position, usually .45V, up to WOT, where it should measure between 4.0V to 4.5V max. The BLACK wire is ground.

[BNaylor]

As Bo pointed out just install it and double check the output. The TPS on a SII 3800 is plug and play providing it was installed correctly.

Just ensure the TPS sensor lever engages with the drive lever on the throttle body shaft. The TPS is self zeroing and not adjustable.

[happydog500]

I found some information and read it over and over. I understand it pretty good except for one part.

When it says, "Once the trouble code is set, the ECM will use an artificial default value for the TP Sensor, and some vehicle performance will return."

This means the TPS is at (something) and when a code is set, it goes to another, or different, "Default value". If it's at a different setting, value, whatever, and I replace it, how does the new one get set from the "default value" to what it was before it was set at the "artificial" default value?

Not sure if I'm able to express what I'm not understanding. Does someone understand what I'm trying to say and understand?

Thank you for replying,
Chris.

[HotZ28]

If you installed a new TPS and it is reading the correct voltage, the PCM will recognize that voltage and use the correct parameters for throttle opening. If you have an incorrect voltage, (out of range) the PCM will use a default value. A scanner will tell you the voltage throughout the full range and of course, you can check the voltage as described above with a DVM. If a code is set and it goes to a default setting, that does not mean it will stay in default if the new part reading is correct. You should clear the stored code after replacing a part, to see if new codes appears!

[happydog500]

Thank you for the replys. I think I have it in mind now. I don't want to keep up with questions on a simple thing like this, but i have one more.
In my Haynes manual, it says AFTER I put in a new TPS, THEN I need to ajust it with a Volt Meter. Why would it say AFTERWADS I need to ajust it?

[BNaylor]

Originally Posted by happydog500

In my Haynes manual, it says AFTER I put in a new TPS, THEN I need to ajust it with a Volt Meter. Why would it say AFTERWADS I need to ajust it?

Because you are using the wrong service manual. Trash the Haynes and forget about Chiltons. The procedures are too general in nature and mostly obsolete.

Stick with a GM FSM. The Haynes procedure is in total contradiction of the GM FSM procedure.

[Bassasasin]

You may not need one.. If you can check the TPS for a constant change of resistance or voltage if its powered... They do get dirty on the internal wipers though..

As you pointed out rough running can be a conflict between what the TPS says and the actual position.. or other things..

Clear the codes and run for a while and double check for the code..
Stores will let you buy, buy, buy till you get the right part.. thats their business. .


Good Luck

[happydog500]

That's a good idea to clear the code and run it to see if I get another one. I have delayed doing this since the cold front came in. It's been in the low teens in the day time, with no garage to work in.

I talked to a friend last night. He will let me use his Volt Meeter and has a garage to work in. One question is; I got info from the local library that has 0.5 at closed throttle, with a smoth increase to wide open it should be approximately 5 volts. If it's running on a "default Value", will the volt numbers be the same? It seems like it might effect the numbers. Even if I clear the code, I might not be able to get to his house without triggering another one.
So, should a Volt Test show the same numbers with a Default value as it will with a normal value? Thank you for helping me with all the replys.

[HotZ28]

Originally Posted by happydog500

If it's running on a "default Value", will the volt numbers be the same?

So, should a Volt Test show the same numbers with a Default value as it will with a normal value?

I can see you are having a hard time understanding what you read about “PCM default valve”! That is understandable, so we will try to put it another way! If I interpret the two questions above correctly, they are the same question, just worded different.

First, I will answer your questions above with a simple yes/no response! The answer is YES!

Now, I will attempt to expand somewhat on the meaning of “PCM default value”. Default Value, is how the PCM responds to incorrect information it receives from the sensor(s). If your TPS is bad, it will normally send an incorrect voltage to the PCM. The PCM will compare that with other inputs and parameters required for an engine to operate properly. If it sees that the TPS voltage is not in-line with what it should be, or what the other sensors say it should be, the PCM will then adjust and switch to the “default value” settings. When operating in the default mode, the PCM goes into “open loop” or “limp home mode” (the same thing). Usually the PCM default value will only keep an engine running well enough to get you home, therefore, the term “limp home mode” was applied to this running condition.

The volt test will tell you what is going into the TPS (5.0V on White wire) and what is being sent to the PCM, when you measure voltage on the Blue wire. Again, the voltage on the white wire is PCM reference voltage (coming from the PCM) and should always be 5.0V. The variable voltage on the Blue wire, is what is coming out of the TPS and sent to the PCM to interpret! The PCM only knows what information it receives from the TPS and it will respond to that information in someway, either in normal mode or default.

Default operation has noting to do with what voltage you read at the TPS!
Again, in order for the PCM to switch to a default setting, a sensor must be out of the normal operating range. An example of that would be; if your TPS is showing 1.5V at idle (closed TB), or under 3.5V at wide-open throttle.

I hope I did not confuse you more, if I did, do not hesitate to ask again!

[Luke.]

Fm Hot Z 28

The volt test will tell you what is going into the TPS (5.0V on White wire) and what is being sent to the PCM, when you measure voltage on the Blue wire. Again, the voltage on the white wire is PCM reference voltage (coming from the PCM) and should always be 5.0V. The variable voltage on the Blue wire, is what is coming out of the TPS and sent to the PCM to interpret! The PCM only knows what information it receives from the TPS and it will respond to that information in someway, either in normal mode or default.

I hope I did not confuse you more, if I did, do not hesitate to ask again!

Well explained; Even I understood it. Thank You !!!

[happydog500]

Thank you very much. I understand it. You explaned it so good, clearly.
When it first happend it ran really rough. Aftere a few minutes it ran good. Never had a problem driving it, even durning the week after.

I checked the wires like the book at the library said to. It said to make sure the wires where stright out of the TPS. Mine come out and are very curved around to go the opposiet direction, almost kinked. I tried to strighten them out but it seemed like it felt like not the thing to do.

Went to Autozone to get the codes cleared. They told me Autozone got sued and now can't remove codes (they will still read them, just not remove).

I went to Shucks. Man, that guy scared me! He plugged in the unit and started the car up. I thought I red someware not to do that. He seemed like he didn't have a clue of what to do. I saw as he scrolled though a "MIL" was bad. He said that they all say that and it's nothing.
He came to "clear codes" and didn't do anything. He unplugged and said OK, it's done.
Car seems to run good. I never got to my frends house to check the volts.

[BNaylor]

What were the stored codes when you took it to Shucks? And out of curiosity what was the original TPS DTC (Diagnostic Trouble Code)? The three possibiities are: P0121, P0122 and P0123.

The most common is P0121. When the conditions for running this DTC are met, the PCM will use the manifold absolute pressure (MAP) sensor to determine if the predicted operating range of the TP sensor is correct. If the PCM detects the TP sensor voltage is out of the predicted range, DTC P0121 sets.

To set a P0122 (TP Sensor Low Voltage) which is an excessively low signal voltage at closed throttle measured with a DMM at the Dark Blue wire the low voltage threshold is around .16 vdc.

To set a P0123 (TP Sensor High Voltage) which is an excessively high signal voltage at wide open throttle (WOT) measured with a DMM at the Dark Blue wire the high voltage threshold is around 4.71 vdc.

So if none of the above is applicable and the SES/MIL light is extinguished at this time then it sounds like your TPS is good and working so no further action is required.

In any event if the TPS is good the following is applicable:

CONDITIONS FOR CLEARING THE MIL(SES LIGHT)/DTC

* The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
* A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
* A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* Clear the MIL and the DTC with a scan tool.

[happydog500]

I beleve I saw a "Code 21" at AutoZone the first time. Not shure what the Shucks code was or if there was one. Maybe I should go back to AutoZone and see if it has a code? I'm leaning towards just driving it and see what happends.

[BNaylor]

Originally Posted by happydog500

I'm leaning towards just driving it and see what happends.

Sounds like a good move to me.

And we look forward to this thread winding down.