Throttle position sensor troubleshooting

[ItchyDong]

So just a recap of where I'm at now. I am getting the error P0123 TPS high voltage. The middle wire of the TPS is reading 12v with the key off/on and disconnected/connected to the TPS. (the other wires are normal) Pulling the PCM does not change this. Pulling the 30amp F6 fuse under the hood removed all power to the center wire. According to the documentation it is for Automatic Shut Down Relay, Powertrain Control Module it also read 12v at the fuse with or without the PCM connected. The PCM is from wranglerfix and they tested it for me and it works without problems. I'm not sure where to go from here but I grabbed the wiring diagrams from the service manual. Looking at them I am not real good at reading these but I cant tell were 12 volts would come from or where the fuse is. Looking for ideas on how to narrow this down. Thank you all for your help so far!

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Assuming all of this is correct (I’m not there so I have to) then this means that a wire from the ASD circuit has rubbed with the tps signal wire. None of these prints are of any help, because they only show how a functioning circuit works. They all carry the same 5 volt reference feed or 5v signal return.

It’s time to go back to the test light and wiggle test and peeling back loom to figure out where those two wires meet up in the harness. This is some serious troubleshooting territory and where the men are separated from the parts changers. You’ll get it.

 

[macleanflood]

Luckily it's a short enough run from the PDU to the TPS.

-Mac

 

[Sargas3]

Luckily it's a short enough run from the PDU to the TPS.

-Mac

I was afraid that was my last option. Well atleast I have a long weekend to get to work. Thanks ill let you know ow how it goes.

 

[Sargas3]

I was afraid that was my last option. Well atleast I have a long weekend to get to work. Thanks ill let you know ow how it goes.

Ok so not as bad as I thought but I started at the wrong end. The short is in the plug that goes into the pcm. Until I took it apart my light never flickered. Now I need to find the correct connection and i should be good. I'll let you know!

 

[Sargas3]

Ok so not as bad as I thought but I started at the wrong end. The short is in the plug that goes into the pcm. Until I took it apart my light never flickered. Now I need to find the correct connection and i should be good. I'll let you know!

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Does anyone know where i could get a replacment pin? Harder to find than I thought.

 

[ItchyDong]

Does anyone know where i could get a replacment pin? Harder to find than I thought.

Excellent job!

If it were me, I’d probably go get me a junk yard plug and splice it in. Huge pain in the ass.

https://connectorexperts.com is an excellent resource. They may not have it in stock, but you can email them and they’ll work tirelessly to find you a solution.

 

[macleanflood]

Excellent job!

If it were me, I’d probably go get me a junk yard plug and splice it in. Huge pain in the ass.

Or get the connector and depin what you need.

-Mac

 

[ItchyDong]

Or get the connector and depin what you need.

-Mac

Yep. Even better

 

[Bammo68]

Ok so not as bad as I thought but I started at the wrong end. The short is in the plug that goes into the pcm. Until I took it apart my light never flickered. Now I need to find the correct connection and i should be good. I'll let you know!

That's a great result! As said before - this level of troubleshooting is becoming a lost art and you nailed it, well done...

 

[Sargas3]

That's a great result! As said before - this level of troubleshooting is becoming a lost art and you nailed it, well done...

Thank you! Pretty happy to get this figured out! Thank you all for all the help! I got couple leads on the connector from jeeps getting parts out. I'll update as soon as inget it done!

 

[Sargas3]

Sooo... good news and bad. I got the plug from wranglefix. He had a couple extras. (great guys!) and put it in taped up everything and not im reading the correct voltage and it moves up correctly when I apply throttle. code is now gone. The bad news is I no longer have spark. I have fuel, I checked the plug and I have 12v from the pin. all fuses are good. nothing from the spark plugs. it had to be something I did but not sure where to start.

 

[macleanflood]

Did you cut everything and splice in the new connector or did you depin and replace that one wire?

-Mac

 

[Sargas3]

Did you cut everything and splice in the new connector or did you depin and replace that one wire?

-Mac

I replaced the 1 wire. And I did test that wire from the plug and it has 12v

 

[Sargas3]

Had not time to work on it today. But was able to test that the coil is not getting spark. and ASD seems to be fine.

 

[ItchyDong]

Verify coil pack has 12 volt supply voltage while cranking.

Use an incandescent test light connected to battery positive. Back probe the coil control wires at the coil pack plug that go back to the pcm. Touch the probe to the t pin while someone cranks. Test light should flash. This will verify the PCM has control of the ignition sequence.

I worry about your PCM after having battery voltage on a 5 volt signal return circuit.

@Wranglerfix would know better than me, but I’m pretty sure coil drivers are a common failure.

Edit: just realized yours is a 99 and not the coil rail set up. Not sure this test will work. The coil driver on the distributor set up might provide ground the entire time the PCM sees a crank signal. Not sure, I’ll have to do some reading.

 

[ItchyDong]

Just verified, the above test will work and verifies the coil driver is functioning properly.

 

[macleanflood]

Makes me wonder if you pulled fuse 18 and put 12v on A20...a power probe would be ideal for this...if it would start.

-Mac

 

[ItchyDong]

Makes me wonder if you pulled fuse 18 and put 12v on A20...a power probe would be ideal for this...if it would start.

-Mac

Pretty sure the problem would be the ground side not the power side. But, I’m not there. Checking for power at the coil is too quick of a check to be jumping power. Rouge voltage is what started this whole thing. No need to introduce a power probe

 

[Sargas3]

I got it! Ok so I tested everything working my way back to the PCM And Again I started in the wrong direction. The plug had the correct 12 volt but the pin inside had been pushed in just a little when I put it together. It was enough. I reseated all the pins. (tip using a large sowing needle to line up each pin as I pushed the plug back together) It started right up. No codes!!!! Again thank you everyone willing to get on here and give me a hand! I really apricate it!

 

[ItchyDong]

I got it! Ok so I tested everything working my way back to the PCM And Again I started in the wrong direction. The plug had the correct 12 volt but the pin inside had been pushed in just a little when I put it together. It was enough. I reseated all the pins. (tip using a large sowing needle to line up each pin as I pushed the plug back together) It started right up. No codes!!!! Again thank you everyone willing to get on here and give me a hand! I really apricate it!

Well. Freaking. Done man. Troubleshooting is the most rewarding part of wrenching to me. There’s nothing like using methods and techniques, and following the clues to isolate an issue. Things like “clean your grounds”, blindly ripping apart a wiring harness to check wires, or automatically sending off a PCM to be tested are common advice on here. A test light can answer almost all these questions in an instant and eliminate guess work and down time.

With the lack of quality in the aftermarket parts market, now more than ever, our TJ’s are going to require actually troubleshooting the issue. Firing the parts cannon and blindly replacing perfectly good sensors with aftermarket junk, and in turn, introducing new faults to an already existing problem can muddy the waters so bad it’ll make your head spin.

You followed the path straight to your answer. Congrats brother.