I've read the FAQs on calibrating the TPS and everyone seems to do it with the TPS plugged in and the car powered up and measuring the voltage drop by sticking a probe through the wire insulation. Wouldn't it just be easier to use an ohmmeter and measure the resistance between pins of the tps with the harness unplugged? It's just a potentiometer right? Does anyone have the proper resistance values to calibrate the TPS this way or is it impossible? Seems to me this would be way easier to do it this way when you have the UIM off the car and in easy reach.

 

You need power to the TPS sensor in order to measure.

The sensor is merely a pot so it seems you could measure it with the UIM off the car like you said. The reason that won't work is because the ECU is referencing voltage from the sensor, not resistance. What we're really doing when adjusting the TPS is ensuring the voltage parameters already burned into the ECU are met by the sensor when the throttle is at certain settings.

Since the ECU references voltage we need to check voltage, not resistance.

 

Right, but voltage drop can be directly correlated to the resistance of the potentiometer. That is to say if you calibrated the TPS to the correct known resistance values then once power is applied you'd get the expected and correct voltage values to the ECU.

BTW: this is how the TPS is calibrated on my other car, and it works fine. This is what prompted my question in the first place.

 

Depends on what the input voltage to the sensor was to start with. Measuring the resistance of the pot doesn't take that into account. The feedback to the ECU from the sensor is a voltage signal so it only makes sense to adjust it properly by checking the voltage specs.

I have not seen "correct known" resistance values from Mazda, only voltage.

 

good question..good answer, always learning :-)

 

I agree.

Im having a problem with my TPS myself so its good that great knowledge is passed onto this site daily.

 

As long as the computer closely regulates the 5V sent to the TPS, measuring resistance should work. I just checked my TPS the other day and everything was in spec. If I get some time, I'll take some resistance readings and post them and their voltage equivalents.

 

Here's what I measured:

Range____Throttle________Resistance____Voltage (DMM)_____Voltage (PFC)
Narrow____closed________411ohms______0.83V________ _____0.78V
Narrow____open_________1680_________5.07__________ ____4.97
Full_______closed________426__________0.40________ ______0.37
Full_______open_________1980_________4.40_________ _____4.32


Resistance was measured from the pin (#2 & #4 from the top) to ground (#1 from the top). And voltage was measured from the pin to ECU ground. Upon further thought, I probably should have taken some more measurements because I could have calculated some fairly accurate tolerance ranges. I guess I'm getting a little rusty in my old age.

Measuring resistance probably isn't the best way to do this, but you at least have some ball park numbers to go from.

 

Your idea is not easier. You already wasted more time asking how to change the procedure than it would have taken to perform it already.

If you want easier, install a PFC and read the voltages from the commander.

DAPDAS!

 

Great, thanks for the help and taking the time to measure these! I'll try and use your measurements as a ballpark while the UIM is off the car and then use the factory voltages once the car is running again.

So it's a waste of time to challenge the status quo? Why isn't my method easier? I've got the UIM off the car with easy access to the pins of the TPS without having to poke holes in anything while trying to see what I'm doing in the dark netherregions of the engine bay. Throwing money needlessly at something is not always the correct answer. Thanks for your helpful input

 

Armitage, your method is correct assuming that the TPS input voltage is clean. The active measurements are checking a few things, not just the TPS.

Yes, TPS is a potentiometer and what the ECU will read is purely based on the impedance of the pot (V=IR).

Quote:
Since the ECU references voltage we need to check voltage, not resistance.

Voltage is dependent on the impedance. So Armitage is correct.
It's a difference of assumptions about the voltage/current going into the TPS. If it's dirty for whatever reason, you may be adjusting the TPS to compensate for another issue.