Q45 tps problem

[95_240]

So I was checking the voltage on my tps and with the throttle closed the highest I can get it to read is .1 volts. At half throttle it will read .45 and at full throttle it reads 3 volts. I went to the junkyard and purchased another tps and it is giving the same readings. With my prior harness it worked fine but not with the new harness. I checked the wiring and it seems fine. Does this seem like a coincidence and I have two bad sensors or does it sound like something else?

Thanks

[95_240]

I tried another tps and I am still having the same problem. I'm getting 5 volts to the power wire and the ground wire is good. My car is having trouble idling and missing really bad between 2000-3000 rpms. I'm guessing this is in part to the tps reading but I cant figure out why it wont adjust above .1 volts.

[Carl H]

how is the power supply to the ecu?
engine grounded well?

[95_240]

Power supply to the ecu is good. Engine has a couple of extra grounds and the ground for the sensor had continuity with the grounds. I just took apart the spare sensor and for it to read .45 volts it has to be rotated 90 degrees past where it should be. The second plug used for verification is pointing straight up.

[95_240]

Just hooked up a new sensor and Im still having the exact same problem.

[Q451990]

Just brainstorming here, but are you sure you're using the correct connector on the TPS? The one with the pig-tail is the one you want... not the one that's actually part of the TPS. That's the secondary TPS and I think is pretty much just open or closed.

I buy these throttle bodies and resell them on eBay, and have never seen a bad sensor, so I think the chance of you getting two that are bad are very slim. We almost never see bad ones in the Q45 forum. Maybe one or two in probably 15 years of internet forum activity...

Check out page EF & EC-222 in the 1994 Q45 service manual available at http://www.nicoclub.com/FSM/ for the correct pins.

Heath

[95_240]

I do have it hooked up to the connector with the pigtail. It actually worked fine before I got a new harness. I checked the wiring and everything seems to be correct. 5v to the red wire, ground has continuity, and the signal is in the middle just giving off low voltages. That's all it needs right?

[Q451990]

Weird... is the harness going to the correct wires? I think only two of the three are used. I don't know what what would happen if it went to the other wire...

Heath

[95_240]

I went and picked up another throttle body to eliminate this as the cause 100%. It is still reading low. Could the ecu be fried or is there other wiring from the f3 plug to the ecu that could be jacked up?

[Carl H]

if you're getting a 5v ref voltage to the tps then the problem is not the ecu but in the wiring somewhere...

[95_240]

I depinned some things to check the wiring. I depinned 48 on the ecu and placed a wire in it and connected it directly to the red pin on the tps. I ran a wire from the black wire on the tps directly to a ground. The tps signal is still reading .15 volts max closed and 1.5 volts max on wot. I'm beginning to think this premade harness stuff is a load of s*** and I was better off with the harness I wired myself.

[biohazardmotorsports]

how long has it been doing this? did you do anything to before this happened? have you done a voltage drop test on the ground side?

[95_240]

I previously had a chasebays harness that the tps worked fine on. I was able to set the tps to .45v closed and it was between 4.5 and 5 volts wot. The harness had other problems so I sent it back and ordered one from wiring specialties. When I went to set the tps I noticed the polarity was switched. This was because I switched the wires because the chasebays harness was pinned incorrectly. When the wires were backwards I can't remember if it read 4-5 closed or if it read low.

[biohazardmotorsports]

i think you just found your problem, what do you mean by polarity switched where at?

[95_240]

The black and red wires were switched but now they are pinned correctly. Even if the polarity was switched I would be getting 4-5 volts through the signal wire with the throttle plate closed so that is not the problem.

[biohazardmotorsports]

have you tried a jumping a good wire from the pcm to the tps for the return signal?

[95_240]

I don't need to jump the signal wire. I can depin it and verify the low voltage.

[biohazardmotorsports]

if your getting low voltage out of the ecu and you have double checked the grounds and powers to the ecu then it would make sense for it to be the ecu. i would try running all three separate wires from the ecu to the tps and see if you get the correct voltages. if it works then you know its the harness. but you probably already knew that. haha

[Q451990]

i would try running all three separate wires from the ecu to the tps and see if you get the correct voltages. if it works then you know its the harness. but you probably already knew that. haha

+1 on that suggestion. Sounds like the most foolproof troubleshooting method. You could even take your spare TPS/TB and hook it up next to the ECU so that you don't have to run long wires all the way around to the engine bay.

Heath

[95_240]

I depinned some things to check the wiring. I depinned 48 on the ecu and placed a wire in it and connected it directly to the red pin on the tps. I ran a wire from the black wire on the tps directly to a ground. The tps signal is still reading .15 volts max closed and 1.5 volts max on wot. I'm beginning to think this premade harness stuff is a load of s*** and I was better off with the harness I wired myself.

I've already hooked it up directly. I'm going to hook this sensor up to a friends car to determine if it is good or not. I never said I was getting low voltage out of the ecu it is reading 5 volts.

[Q451990]

So does it work if you hook it directly to the ECU?

[95_240]

Nope. Still gives off the same readings. It doesn't make any sense to me.

[biohazardmotorsports]

what are the things that your working with? what engine and ecu. try and take some pics of what your doing you may be doing something wrong? not saying that you are but if you have your tps hooked up to the ecu correctly and your reading voltage on the correct wires and the voltage doesnt change then your tps is bad. your on the three wire pigtail right? What wires are you reading on with your meter?

Here is the pin out for a R32 RB20det
Ground pin #30
TP power pin #48
Throttle signal # 54

[locoluna825]

I am having the exact same issue with a friend’s car. Series 1 rb25det, I did the harness. Its been throwing a TPS circuit code. I checked all of the same items above as the OP, I get 5v power, ground but no signal coming out of the TPS sensor. I’ve opened the wiring harness twice now, checked continuity of the wires, and triple checked the pining, I cannot get any signal out of the TPS sensor on his car. We tried 3 different TPS sensors. I can plug each of those 3 TPS sensors into my harness on my rb20det and get a signal out of each one. But cant get a damn signal out of any of them on his. It just also recently threw a Temp sensor circuit code.
On the series 1 rb25det and rb20det's the ground for the TPS sensor and temp sensors are joined together down near the ECU in the wiring. The only thing I have not tried was unplugging the temp sensor to see if I still get a ground to the TPS. (Since I think it would be grounding back up through the temp sensor on the manifold), and actually opening the ECU up to check for some sort of apparent damage to the board or components. This leads me to believe there is some sort of problem within the ECU grounding the sensors since it is now throwing both those codes and they share that ground from pin 30.

[noodl35]

I know this sound easy but I had this issue before and it turned out to be that the battery in the DMM was low!

[OutToWinPAHC]

When I was doing the AEM from PFC I had trouble understanding some of the repinning and one thin I missed was signal ground and my TPS did this, So check signal ground to the TPS via continuity.