Differnce in TPS voltage signal from ECU and TCU

[Infinitiguy19]

I have this portable consult and I am getting two different readings from the ECU and TCU (Engine Control Unit, Transmission Control Unit) in the ECU I get a fluctuating reading of .70 volts from the TPS (Throttle Position Sensor) on the TCU I get a reading of .72 volts. Is the above normal?

Also in the Engine part of the OBD Scan Tech the Closed throttle Position sensor reads that the throttle is closed.

In the Transmission part of the OBD Scan Tech the Closed throttle Position sensor reads that the throttle is not closed intact there is no reading at all.

Why is that?

And I think this is why the A/T Check is not working.

[Q45tech]

The ECU and TCU use the TPS to create 10 or 8 steps of throttle position.Idle [0%] , 10%, 20%......................WOT ends up being >3.79 volts

The charts in AT section explain that part of different steps.

Only the idle to 10% [or 12.5%] is critical.

The TPS is a backup check against MAF voltage for ECU, inthat as long as they agree within 20% the MAF is assumed to be correct [since air temp and pressure vary].

At X rpm and Y TPos with Z air density flow...................OBDII adds an air temp sensor to the equation as a triple check. Some cars add a barometric sensor and a MAP to help zero in on errors or accuracy.

[Infinitiguy19]

So basically they are supposed to have the same voltage right or the voltage should be with in 20% of each other and the MAF?

[Q45tech]

Not necessarily, that the voltages are equal between TPS and MAF as the MAF depends on rpm.

Obviously you can reach a highish rpm in a low gear slowly [TPS low] yet MAF can read high.

The ecu examines steady state cruise [even 120 mph cruise @ 4,000 rpm on level or down hill] can be done with low TPS [30-40%] eventually.

If TPS was at 20% yet MAF was at 80% the ecu would know TPS was reading wrong. The converse might be a warm day on a Denver mountain top MAF 50% with a 100% TPS [WOT].

[Infinitiguy19]

Ok, what about the difference that I get when I read the ECU and when I read the TCU when I look at the TPS voltage.

Is it normal to have the ECU TPS voltage reading be different from the TCU TPS voltage reading?

Could that mean the TPS is bad because I have tried 2 different TCU?

[Q45tech]

Reading voltage with a VOM is not the same as using a Consult to see what ECU/TCU says it sees. The VOM method is accurate but not germane in this case.

[Infinitiguy19]

OK, I will check the FSM for the procedure on checking the TPS voltage at the TPS and ECU/TCU And will get back to you.

Even though I think its easier to swap out a throttle body with the TPS already on it that is untouched (hopefully).