P0121 TPS pending code and losing 12V low reference ground to ECM. lntermittent high ldle and late shift issue.

mrbreezeet1

mrbreezeet1

Joined
Aug 4, 2021
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Had this in another thread, but thought I'd ask over here.
P0121 TPS pending code.
TPS was cheap enough, decided to fire the part cannon a little, and replaced the TPS!
No joy though.
Did some testing while the motor was Idling high.
It looks like I am losing my TPS low reference from TPS terminal "B" back to the ECM's commanded ground.
I've inspected for rodent damage at the air box where the ECM resides, no family of critters present. I've done a wiggle test everywhere that I can see with the car good and warmed up.
Looking at the schematic it appears to me that the low reference return ground to the ECM from the TPS is not shared by any other sensors. If I can't find this intermittent open to my low reference return ground, do you guys in the know, see any issue with just piggybacking a wire along the harness from the TPS to the ECM?
Really not the way I wanted to fix it but I'm sort of running out of ideas!
Issue is intermittent have been driving for a good half hour today and idle and transmission is shifting fine ATM.

My Car TPS 1.jpg
 
I am assuming you have a constant 5v reference at the TPS (A). Running a new wire from the PCM's # 61 to the TPS-B connection would be my idea too. I would also verify the TPS signal (C) is reaching pin 66 - C2 at the PCM as well. If that doesn't resolve the issue, you may have an issue with the PCM.

Being intermittent, I would suspect a connection problem between the PCM and the TPS sensor or a solder joint issue within the PCM.
 
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Lubener said:
I am assuming you have a constant 5v reference at the TPS (A).
Running a new wire from the PCM's # 61 to the TPS-B connection would be my idea too.
I would also verify the TPS signal (C) is reaching pin 66 - C2 at the PCM as well. If that doesn't resolve the issue, you may have an issue with the PCM.

Being intermittent, I would suspect a connection problem between the PCM and the TPS sensor or a solder joint issue within the PCM.
Click to expand...
Good call on the bad solder joint! I didn't think of that. Maybe I could peck on the ECM a bit while I have the fault.
I would have to think the TPS signal is reaching pin 66-C2 at the PCM and A good 5V reference as I am getting a good sweep on my scanner app,
although I didn't have a DVOM at pin 66 when the fault occurs.
I did have a constant 5V reference at the TPS when first testing, although, again, I didn't have the DVOM at pin A when the fault occurred.
The darn thing is making me mad as it comes and goes when I'm trying to test it!
I was thinking of getting a new TPS wire connector with the longest wire leads I could find and splicing that into the wire harness with the hopes that the fault is close to the TPS sensor.
They should make one of those TPS sensor male end connectors with about a 10-foot 3 wire lead on them, then you could rewire it all the way to the ECM.
Thanks Lubener!
1697348305363.jpg
 
The reason I suspected losing the low reference ground return to ECM too, is because when I get the fault with the car idling the TPS scanner value jumps from 0, up to ~39% all by itself. I then turned the motor off, and with KOEO depress the gas pedal down and release a few times, the value goes back to "0" as if the ECM is resetting it back to it's base value.
I could be wrong though.
 
Unless I "follow my gut" and just go ahead and run the new wire from the TPS terminal B to ECM terminal 61 and run it a few days and see what the heck happens.
 
mrbreezeet1 said:
The reason I suspected losing the low reference ground return to ECM too, is because when I get the fault with the car idling the TPS scanner value jumps from 0, up to ~39% all by itself. I then turned the motor off, and with KOEO depress the gas pedal down and release a few times, the value goes back to "0" as if the ECM is resetting it back to it's base value.
Click to expand...
And to Add. And then the percentage again sweeps from 0% to 100% when depressing the gas pedal.
So I think the blue signal wire C and the A 5V Gray reference wire A are OK at this point.
Worse case, I'm going to just run all 3 wires and be done with it.
Found a guy on Ebay that can make up a 3 wire TPS connector 10 or 15 feel long whatever I want!
 
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Have you tried disconnecting the wire plug from the TPS output and measuring the resistance between "C" and "66"? Then measure the resistance between "B" and "61" and compare values. The ohm readings should essentially be similar since they both originate at the TPS and terminate at the PCM.
 
Nukeman7 said:
Have you tried disconnecting the wire plug from the TPS output and measuring the resistance between "C" and "66"? Then measure the resistance between "B" and "61" and compare values. The ohm readings should essentially be similar since they both originate at the TPS and terminate at the PCM.
Click to expand...
Right. No not yet I want to do that too.
So do you think if between B and 61 is indeed my problem, it might show higher resistance, even when the fault is not present? (Maybe it's hanging on for dear life by a few strands 😂}
If that's the case, I guess it might read higher resistance?

I'll do that next.
 
mrbreezeet1 said:
Right. No not yet I want to do that too.
So do you think if between B and 61 is indeed my problem, it might show higher resistance, even when the fault is not present? (Maybe it's hanging on for dear life by a few strands 😂}
If that's the case, I guess it might read higher resistance?

I'll do that next.
Click to expand...

I'm actually thinking it may be something simple like oxidation or corrosion on the plug contact pins on one or both ends of that wire. I'd certainly use a good contact cleaner like DeOxit Gold on the pins and plugs before reconnecting them to the TPS and PCM.
 
Nukeman7 said:
I'm actually thinking it may be something simple like oxidation or corrosion on the plug contact pins on one or both ends of that wire. I'd certainly use a good contact cleaner like DeOxit Gold on the pins and plugs before reconnecting them to the TPS and PCM.
Click to expand...
Thanks I'll check it out, That would be nice!!
I didn't clean the TPS end contacts but that end "looks" OK at least.
Weather was rotten today, as well as me feeling the same, I wish I could have worked on it. I have to work outside.
Ordering DeOxit now!
 
mrbreezeet1 said:
Thanks I'll check it out, That would be nice!!
I didn't clean the TPS end contacts but that end "looks" OK at least.
Weather was rotten today, as well as me feeling the same, I wish I could have worked on it. I have to work outside.
Ordering DeOxit now!
Click to expand...
I've been following your post, and I do agree to check the pins/clean them first. You're at least getting a reading from the tps sensor. When my ground wire died on my 96 civic (for the EGR valve) it stopped completely. Turns out the wire just broke after 25 years! And no signal was getting through. That's what makes sense for yours, at least to check it/clean it first before moving forward

The other part you posted about that long wire being created, that's something that could be used to test the wiring if this cleaning/de-oxidizing doesn't work.. Sounds like you're headed in the right diagnostic direction!(y)
 
researcher said:
You're at least getting a reading from the tps sensor. When my ground wire died on my 96 civic (for the EGR valve) it stopped completely.
Click to expand...
Yeah, It's Intermittent!
researcher said:
The other part you posted about that long wire being created, that's something that could be used to test the wiring if this cleaning/de-oxidizing doesn't work.. Sounds like you're headed in the right diagnostic direction!(y)
Click to expand...
Thanks researcher! I was surprised I found a lead like that too! It would be good for testing too!
I'm probably gonna buy a short one too, as posted in my picture above. for easier testing of my old sensor on the bench, just for S&G's!
And for easier testing of this style TPS/connector on the car!
Well, and then there is * this connector, I could make my own 10-foot repair harness if I wanted to!
(I don't mind splicing, but I always felt like the less splices = less spots to become compromised!}
I already have 22 AWG wire ordered!
* https://www.amazon.com/dp/B07RFSN1C...ZM43YV8N&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it
Conn.jpg


researcher said:
I think (hey just my opinion) that the brush on would work well.. No need to spend that much $$$ when a little is all you need. Be careful those reviews said it was easy to spill this tiny bottle....... :eek::eek:
Click to expand...
Thanks!
Yeah, I have to watch my money a bit these days!
 
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mrbreezeet1 said:
Yeah, It's Intermittent!

Thanks researcher! I was surprised I found a lead like that too! It would be good for testing too!
I'm probably gonna buy a short one too, as posted in my picture above. for easier testing of my old sensor on the bench, just for S&G's!
And for easier testing of this style TPS/connector on the car!
Well, and then there is * this connector, I could make my own 10-foot repair harness if I wanted to!
(I don't mind splicing, but I always felt like the less splices = less spots to become compromised!}
I already have 22 AWG wire ordered!
* https://www.amazon.com/dp/B07RFSN1C...ZM43YV8N&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it
View attachment 183675


Thanks!
Yeah, I have to watch my money a bit these days!
Click to expand...
Hey I know exactly what you're talking about, saving money.. I'm right there with ya!

And I feel the same way about splices, the less a wire is messed with, the better! I do like those taps you found to help you aid in testing, very nice!

Be interesting to see what you find. I was thinking about it and after 22 years, the wiring is bound to bring some issues. I ran into that with the 96 Civic.. Especially if you have to move a wiring harness because you need to remove/install a part.
 
researcher said:
Hey I know exactly what you're talking about, saving money.. I'm right there with ya!

And I feel the same way about splices, the less a wire is messed with, the better! I do like those taps you found to help you aid in testing, very nice!

Be interesting to see what you find. I was thinking about it and after 22 years, the wiring is bound to bring some issues. I ran into that with the 96 Civic.. Especially if you have to move a wiring harness because you need to remove/install a part.
Click to expand...
Yep 22 Years old. She only has 108,XXX K on her too!
Didn't do anything on it today though, did drive it around ~ 1/2 hour though, no issues at all :eek:
I will be sure to update what I find though!
 
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