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partial short to ground on tps signal wire,,,driving me nuts

posted May 25, 2016 01:49:24 by john deaver
i've got a problem thats driving me nuts...on my tps wires (cable) i have a 5v ref..00 on the ground wire and 2.5 volts on the signal wire... (wires unplugged from the tps) I cant seem to find out why this is or what to do to solve this
I swapped engine computer and there is no change.. I know the signal is a shielded signal return wire, I tried shaking the harness yet the the proper voltage would not return..can someone shed some light on this seeing that i dont understand much about shielded wires





















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7 replies
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Tyler said May 25, 2016 02:05:34
Hey John! For our reference, what kind of car are you working on?

If there is truly supposed to be 5V on the signal wire with the sensor unplugged, then the other possibility is excessive resistance in the signal wire somewhere. Unfortunately, this still means you're looking for a wiring problem...

Are you trying to address a specific TPS problem or are there other symptoms?

I understand your concern about the shield on the TPS signal wire, but I don't think it changes much about how to go about this diagnosis. I'd suggest doing another voltage check at the PCM TPS signal pin, and go from there. Low voltage at that point would suggest a PCM problem or a short (like you said), while 5V would suggest high resistance.
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john deaver said May 25, 2016 02:19:53
thanks for the reply.. i have ruled out the pcm as the culprit for i swapped it already and no change on the signal wire same 2.5 volts from pcm to tps.....i think it the signal wire but keep getting fluctuations while trying to ohm the wire....i have a old harness here think i'll try and use the tps signal wire from it and switch it and see (it from the the same engine nissan qg15)
hope thats a fix other wise gonna need a new harness.... on more thing how do you take out the wire from the computer as i try to swap it watched a few videos on youtube about replace harness wires but just can;t seem to get it out...
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john deaver said May 25, 2016 02:30:36
for clarity my transmission would not shift...I dont know much about transmissions so someone told me to look at some sensors...when i checked the tps( 6 wire )the tps was not carrying proper signal voltage,,,,,,,, on the first three wires..5vref was good as well as the ground but the signal was 2.5 all wires unplugged..the other three wires (tps switch had no voltage on any of them) not a problem really obviously I junped the wires on the tps swsitch side and the volts returned.. however the tps signal remain 2.5
so before I carry the car to a transmission guy i wanna make sure my sensors are working properly...my forward gears wont shift but reverse gears works fine
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Noah said May 25, 2016 11:28:06
Can you watch the throttle position on a scanner? Might be able to save yourself some tail chasing if you can verify the computer is seeing the signal and it's being updated with movent of the accelerator.
Try taking a voltage measurement on the signal wire plugged in, disconnecting the sensor could be effecting the voltage on the signal wire.

Does your speedometer work? I've seen lots of no shift conditions caused by bad bad input.

Like Tyler said, if we knew what year make and model car you are working on, we could offer more help.
Massachusetts, USA
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RassielCotoMedina said May 25, 2016 19:20:04
are you sure that the wire where you have 2.5 volts is the signal wire? could that be the ground wire?
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john deaver said May 25, 2016 21:29:30
rassie ..i'm sure did this car many times.....its mine....

Noah .. its a nissan QG 15 engine thats on the almera engines..I think in america you call them n16. Its about late 90's to early 2000's ..watched it on scan ,voltage is about .21 of a volt. I think its the wire as i already changed the computer....but this 2.5 on the signal wire when unplugged is a first for me..tell me what you think
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RassielCotoMedina said May 26, 2016 13:45:40
take an ohm resistance at the signal wire, and a ohm resistance between batt+ and signal wire
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