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TPS disconnected

Tiny
SAIF EL-DEEN ESSAM
  • MEMBER
  • 2007 HYUNDAI VERNA
  • 1.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 70 MILES
TPS disconnected, connecter shows 5v on +ve and signal terminals, 5.7v on ground, what is causing this problem?
Thursday, April 23rd, 2020 AT 2:34 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,740 POSTS
Hi,

First, this model isn't offered in the US, but we have the accent which I believe to be the same vehicle. I will try to help. The schematics I have may be different.

On the accent there are three wires to the TPS. Yellow is sensor signal, blue is ground, and green power. Are those the same as your vehicle? If they are, there should't be 5.7V on ground which I feel you already know. Since you basically have 5v on all three wires, my first suspect is the connector has shorted internally and allowing power to each pin.

Most importantly, let me know if the wire colors you are dealing with are the same. I don't want to jump ahead and provide incorrect information.

Let me know.
Joe
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Thursday, April 23rd, 2020 AT 5:29 PM
Tiny
SAIF EL-DEEN ESSAM
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Thank you for your fast response. Well, the car has gone through tons of repairs and even its transmission, ECU, motor and almost everything (except the car chassis) was changed lol, the connectors were kind of remade because the car transmission was replaced from manual to automatic, so the TPS has 3 wires, 2 green which are the +ve and signal, 1 grayish black which is the ground wire. I guess the transmission replacing process messed the whole thing up.

I heard from some people suggesting that the problem may be due to a short-circuit on the ECU board or on the TCM.
So, how to make sure of the main cause of this problem? And why does the ground wire gives 5.7v not even 5v?

I have attached photos of the connector and the TPS.
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Thursday, April 23rd, 2020 AT 6:50 PM
Tiny
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I really believe that is where the problem lies, the ground. It shouldn't have 5.7v unless something has shorted in the PCM or a circuit producing 5.7v has shorted to this ground. Just for curiosity, if you disconnect the PCM, do you still have power to ground?

Please bear with me. Since the wiring colors are different, chances are the design is as well. Also, was the PCM replaced to match the AT you installed?
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Thursday, April 23rd, 2020 AT 7:35 PM
Tiny
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Sorry for the late reply.

I dont know what is PCM, what I concluded now is something weird, there are 2 control units, the ECU (manual engine control unit with only 1 connector) and another control unit for the automatic transmission

There are 2 situations.

First situation is transmission won't go higher than the 2nd gear no matter how high the RPM is with the 3 wires of the TPS as follows:
Voltmeter between battery ground and:
1- TPS +ve terminal gives 5.03v
2- TPS - ve terminal gives 5.70v
3- TPS signal terminal gives 5.03v

Second situation is when I connect OBD device it reads that TPS has a problem but I was shocked to find that the problem of gear changing vanishes, it easily goes to the 4th gear with normal RPM and no problem at all with the terminals as follows:
1- +ve terminal gives 5.03v
2- -ve terminal gives 5.70v
3- Signal terminal gives 0.00v

Once I disconnect the OBD device, the problem of gear changing returns and the signal terminal goes back to 5.03v.
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Saturday, April 25th, 2020 AT 9:50 AM
Tiny
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Hi,

Without schematics for this specific vehicle, it's hard to say. I believe when you are attaching the OBD scanner, you are providing a ground and allowing things to function properly. Check to make sure there are no ground issues. Check the main ground between the battery negative and the engine block. Also, check to make sure the grounds to the body as also in good condition.

As far as 0v from the signal wire, that is correct. It should be 0v until it is running. Then you will get a voltage signal. That is why I feel somehow the scanner is producing a ground for the circuit. When it's disconnected, power is seeking ground via the signal wire.

As far as the modules, yes on newer vehicles with an automatic transmission, there is what is called a TCM (transmission control module).

Sorry, I wish I could be of more help. Without seeing an actual wiring schematic, I don't even know where to tell you to check.

Let me know.
Joe
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Saturday, April 25th, 2020 AT 10:49 PM
Tiny
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Unfortunately, since this car has been manipulated too much, there're no valid schematics for it.
I connected the chassis ground (Pin 4) to signal ground (Pin 5) on the OBD connector and the problem is solved. What does this indicate?
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Friday, May 1st, 2020 AT 2:25 PM
Tiny
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Is the vehicle now running? Honestly, it sounds like someone disconnected or damaged the signal ground. Ugh! I feel bad for you trying to fix this one.

Joe
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Friday, May 1st, 2020 AT 6:30 PM
Tiny
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It works so fine like never before, it's like a puzzle. Haha
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Friday, May 1st, 2020 AT 7:44 PM
Tiny
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Wow! That's good news. Honestly, I wish people would fix things right rather than modifying things like wiring. The problems always end up handed over to someone else. In this case, you. Regardless, you did a great job. I'm glad to know it's running again.

Take care of yourself and please feel free to come back in the future if you need anything.

Joe
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Friday, May 1st, 2020 AT 9:45 PM

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