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Old 10-21-2018, 06:21 PM   #21
OldNuc
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1998 SC2
Default Re: TPS woes

The problem is likely inside of the PCM. Regardless of where the TPS is set physically the PCM will assign the value of 0.37-0.4v to the data out at key ON, the actual voltage may be quite different. Insulation piercing probes are real handy at this point.

--5v reference to block ground
--5v reference to TPS(PCM) ground
--TPS signal to TPS ground, throttle closed
--TPS signal to block ground, throttle closed

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Old 10-22-2018, 12:05 PM   #22
Saturn Night
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Default Re: TPS woes

Quote:
Originally Posted by RobertGary1 View Post
Strange datapoint
Heading out for some dr mandated cardio I realized my multimeter was still hooked up to back probe the pcm across the tps sensor and tps ground (not reference ). So for kicks I turned on the multimeter and turned on the ignition. Got 0 volts. Figured the probes have slipped out so I pressed the gas. It reacted. Then back at idle the voltage very slowly stated to climb until it reached 0.40.

Got my bicycle ready and thought maybe Iíll try that again. This time without touching the throttle. Turned on the multimeter, tuned on the ignition got 0 volts. Waited about 5 seconds and the voltage slowly started to climb. About 0.02 volts/second until it reached 5v.

After my ride I might switch up my set up to read across the tps reference and tps ground and see if itís the same.

Iíve never tried this type of test before; this seems like itís wrong. The PCM shouldnít have to warm up to have proper reference voltage? Or maybe itís normal for some strange reason.

-Robert
Have you tried replacing the connector pigtail and some of the wiring? I have read over the responses and your issues, which sounds like a loose electrical connection.

The TPS is nothing more than a similar type of resistor found in Tyco RC track car controllers, or the resistor used for the fuel pump sending unit to the gauge.

As the butterfly opens, there is a little metal piece that moves along the coil inside the sensor, which adds or takes away resistance, which is how the voltage signal being sent from the PCM is changed.

You can test a TPS with an ohm meter, on the pins and see how they work.

Unplugging the sensor will default the PCM to "0" resistance, so the full 5v signal is commanded by the PCM, but will then set a DTC because no signal is returned and you have a broken circuit.

...
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"He checks the gas, and fills the oil....."

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Old 10-22-2018, 12:52 PM   #23
RobertGary1
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2006 VUE 3.5L
Default Re: TPS woes

Quote:
Originally Posted by Saturn Night View Post
Have you tried replacing the connector pigtail and some of the wiring? I have read over the responses and your issues, which sounds like a loose electrical connection.
Yes, 3 pig tails, 3 TPS's and 2 TB's. See original post for discussion of bad connection.

-Robert

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Old 10-22-2018, 12:56 PM   #24
RobertGary1
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Default Re: TPS woes

Quote:
Originally Posted by OldNuc View Post
The problem is likely inside of the PCM. Regardless of where the TPS is set physically the PCM will assign the value of 0.37-0.4v to the data out at key ON, the actual voltage may be quite different. Insulation piercing probes are real handy at this point.

--5v reference to block ground
--5v reference to TPS(PCM) ground
--TPS signal to TPS ground, throttle closed
--TPS signal to block ground, throttle closed
The problem now is getting it to happen. I've got a multimeter taped to my dash probing the TPS signal across the TPS ground. I'm waiting for a P0122 to be thrown or even a bad idle.

I noticed that the EGR and MAP share the same 5v reference circuit so I think I'll compare it to see if it also has a slow warm up. The 5v reference circuit for the TPS takes several seconds to come up to voltage if the PCM is "cold" but immediate if the PCM has had power in the last few minutes. I'm not yet certain this isn't normal though. That in itself doesn't throw a code likely because the PCM is comparing the TPS signal with the TPS reference.

-Robert

Last edited by RobertGary1; 10-22-2018 at 01:09 PM..

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Old 10-26-2018, 06:13 PM   #25
Saturn Night
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Default Re: TPS woes

Quote:
Originally Posted by RobertGary1 View Post
Yes, 3 pig tails, 3 TPS's and 2 TB's. See original post for discussion of bad connection.

-Robert
Ahh, ok. I didn't notice you had replaced the connector already. I did see the other repairs.

I don't much about PCMs, when TS, other than a bad PCM doesn't always code or trigger the light.
You could have an issue with a fried Quad Driver Circuit, of the MAP/EGR reference voltage are on the same circuit.

Replacement/Reprogramming the PCM may be your remedy to this one. I'm going to just follow this thread, since Nuc knows more about this than I do.

...
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"He checks the gas, and fills the oil....."

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Old 10-26-2018, 08:56 PM   #26
OldNuc
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1998 SC2
Default Re: TPS woes

Quote:
Originally Posted by RobertGary1 View Post
The problem now is getting it to happen. I've got a multimeter taped to my dash probing the TPS signal across the TPS ground. I'm waiting for a P0122 to be thrown or even a bad idle.

I noticed that the EGR and MAP share the same 5v reference circuit so I think I'll compare it to see if it also has a slow warm up. The 5v reference circuit for the TPS takes several seconds to come up to voltage if the PCM is "cold" but immediate if the PCM has had power in the last few minutes. I'm not yet certain this isn't normal though. That in itself doesn't throw a code likely because the PCM is comparing the TPS signal with the TPS reference.

-Robert
I would check the other sensors on the 5V ref bus. That slow rise to 5V is indicative of a failed circuit in the PCM unless you see the same thing on the other loads. It should be instantaneous upon key ON though. Might be worth the effort to give it a hard look.

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