# What happens when a TPS dies?



## leebro61 (Nov 7, 2001)

My car is a vr6 on SDS, running an obd2 vr6 throttle body. The car had been sitting for awhile so I finally replaced the battery and took it for a ride. The car was hesitating at low load/low rpm/low gear but I figured it was because I hadn't completely nailed the tune and I had just swapped in a set of cams. I also noticed at WOT the car seemed to bog and then open up at ~4200 rpm. I also assumed that the tune was off on this, so I went home to check the datalogs.
Turns out my logs weren't showing any throttle positions >50%. I then checked the TPS voltage output by manually moving the throttle plate. When I configured my TPS input to the datalogger previously, I was getting ~0.5V at 0% throttle and ~4.3V at 100% throttle. Now I am seeing ~0.27V at 0% throttle and ~2.4V at 100% throttle.
Obviously this is the problem... but I just wanted to know if the reduced voltage is the surefire sign of a broken TPS or if I have another issue that is causing the TPS to output this way (battery, wiring, etc.).
Thanks for any insight http://****************.com/smile/emthup.gif


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## need_a_VR6 (May 19, 1999)

*Re: What happens when a TPS dies? (leebro61)*

Check to make sure the feed voltage is ~5v before you buy a new tps.


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## chris24g (Jan 12, 2000)

*Re: What happens when a TPS dies? (leebro61)*

You can also double check by measuring the resistance of the TPS sensor at different throttle positions. Don't know what they are offhand but probably can be found in the megasquirt threads.


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## leebro61 (Nov 7, 2001)

*Re: What happens when a TPS dies? (chris24g)*

I will investigate today and see what I can find


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## leebro61 (Nov 7, 2001)

*Re: What happens when a TPS dies? (leebro61)*


_Quote, originally posted by *leebro61* »_I will investigate today and see what I can find









I am seeing +4.99v on the power wire.


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## leebro61 (Nov 7, 2001)

*Re: What happens when a TPS dies? (leebro61)*


_Quote, originally posted by *leebro61* »_
I am seeing +4.99v on the power wire.









Still have this issue. Somebody suggested to check the power wire when the throttle position is opened to make sure the voltage doesn't drop under load. Voltage stays rock solid from no throttle to full throttle. I tried another throttle body (of unknown condition) and I'm getting the same results.
Does this sound like two bad tps'?


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## leebro61 (Nov 7, 2001)

*Re: What happens when a TPS dies? (leebro61)*

Does anyone know if the tps sensor from an obd2 aba throttle body can be swapped onto a vr6 housing? It seems like the obd2 aba throttle bodies are more plentiful and cheaper...


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## leebro61 (Nov 7, 2001)

*Re: What happens when a TPS dies? (leebro61)*


_Quote, originally posted by *leebro61* »_Does anyone know if the tps sensor from an obd2 aba throttle body can be swapped onto a vr6 housing? It seems like the obd2 aba throttle bodies are more plentiful and cheaper...


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## VWn00b (Mar 4, 2005)

*Re: What happens when a TPS dies? (leebro61)*

I've got a few VR OBD2 and ABA OBD2 throttle bodies if you want them. Let me know.


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## leebro61 (Nov 7, 2001)

*Re: What happens when a TPS dies? (VWn00b)*


_Quote, originally posted by *VWn00b* »_I've got a few VR OBD2 and ABA OBD2 throttle bodies if you want them. Let me know.

I would love an obd2 vr6 throttle body. Do you have any that are in KNOWN good condition? Would be even better if you could test one...


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## leebro61 (Nov 7, 2001)

Still having this same issue. I tried a brand new throttle body and I'm only seeing a slight improvement in WOT signal voltage. Would appreciate any new ideas to test


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## ValveCoverGasket (Mar 20, 2002)

where were you grounding your meter when you tested for 5v on your power wire?
use the ground thats coming up to the tps, to make sure that your ground pin is good

check continuity on your signal wire back to the ecu also, make sure that isnt rubbing or touching something, or that you dont have a ton of resistance somewhere in that line.


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## leebro61 (Nov 7, 2001)

I was grounding the multimeter from the positive pin to the ground pin, but I also tried with the ground pin straight to the chassis, with the same results. I also tested resistance from the ground pin to the chassis and it was relatively small.


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## need_a_VR6 (May 19, 1999)

What TB pins are you using? There's a low range and a high range tps in that tb.. maybe your wiring isn't right from the get go.


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## leebro61 (Nov 7, 2001)

I'll have to dig up the pin diagram I had as I've checked for this issue before. I'm guessing this isn't the case since I had full range operation at one point (with the same pins I'm using now), but I'm willing to investigate


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## need_a_VR6 (May 19, 1999)

Does the voltage output of the TPS change if you pull the signal wire out and just measure it with nothing else connected?


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## leebro61 (Nov 7, 2001)

When you say voltage output, you mean signal voltage, correct? If so, I have read the voltage at the throttle body connector signal pin as well as my wideband controller (the final destination for the signal) with very similar results. On both, the voltage increases as throttle angle increases.


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## need_a_VR6 (May 19, 1999)

Yeah on the signal pin, check the pin with NOTHING connected to it. Something downstream might be dragging it down.


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## leebro61 (Nov 7, 2001)

From another thread:

1. actuator +12V/3A (idle control)
2. actuator GND (idle control)
3. throttle closed = pin 7 / open = ∞
4. GND
5. TPS (0,6V closed / 4,3V full)
6. Not connected
7. +5V
8. Not needed (TPS with smaller range)

Right now, I have:

GND: Pin 4
+5v: Pin 7
Signal: Pin 5

Paul, I know you had mentioned in the past that you had to flip the power and ground to get the right trending (increased signal voltage with increased throttle), however this orientation is the one that gives me the right relation between signal voltage and throttle position.


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## need_a_VR6 (May 19, 1999)

All I remember from that is I had the OBD2 tb plug and I had to give the brown/stripe wire 5v to make it work with OBD1/MS (0v = closed, 5v = open).


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## leebro61 (Nov 7, 2001)

need_a_VR6 said:


> Yeah on the signal pin, check the pin with NOTHING connected to it. Something downstream might be dragging it down.


Paul,

You win. I could have swore I tried this before, but I guess not. If I read at the pin, with only the power and ground connections, I get ~0.7v closed and ~4.3v open. I cut the signal wire shortly before it connects to my ecu and measured the voltage there, with similar results. It appears that somewhere within the ecu the voltage is getting "drug down". What sort of things can cause voltage drops so that I might know what to look for?


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## ValveCoverGasket (Mar 20, 2002)

wow strange results
im curious to hear the answer as well :beer:


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## need_a_VR6 (May 19, 1999)

Could be something wrong with the SDS, internal short, etc. If that's the ONLY place the wire goes, I'd call SDS.


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## ValveCoverGasket (Mar 20, 2002)

seems an odd, low voltage non-driver circuit to fail like that, obviously something is up though... definitely curious to hear the outcome :beer:


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## leebro61 (Nov 7, 2001)

need_a_VR6 said:


> Could be something wrong with the SDS, internal short, etc. If that's the ONLY place the wire goes, I'd call SDS.


I wrote them an email last night, and they are usually pretty good about responding back to tech support questions. If I don't hear from them in a day or so I'll give them a call. I actually pulled the ecu and opened it up expecting to see something fried, but to the naked (untrained) eye it appears fine.

The signal wire also goes to my PLX R500 wideband module, so I'll disconnect that and try again to verify it isn't a PLX issue.


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## leebro61 (Nov 7, 2001)

Had an email back first thing this morning. After a few more emails clarifying the situation, it looks like I'll be sending in the ecu for a diagnostic.


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## need_a_VR6 (May 19, 1999)

Any change disconnecting it from the PLX at all? Keep us posted.


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## leebro61 (Nov 7, 2001)

need_a_VR6 said:


> Any change disconnecting it from the PLX at all? Keep us posted.


I disconnected the PLX and there was no change in the signal output. Looks like I'll be sending the ecu to SDS... will keep you guys updated on the outcome.


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## leebro61 (Nov 7, 2001)

leebro61 said:


> will keep you guys updated on the outcome.


Apparently the chip was bad/damaged. Not exactly sure how/when that happened, but I'm glad to have the issue resolved.


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