Throttle Position Sensor-wrong voltage

[DavidC]

Glad you kinda have things working again. If there was betting going on I guess I would lead to the spliced Y. From what I understand it is not a splice like I would think of but rather they are stripped and wrapped together then taped. A recipe for disaster.

 

[Solar1]

yes, and by the way, I did double check the ground runs to the A4 terminal. The ground to the speed sensor and the TPS were real good. My test drive today showed the Overdrive was activating at the correct speed (about 45 to 50 mph), but I did notice a little "slipping" or what I think is termed hunting. That usually happened before when there was a TPS issue. I will check into this more closely tomorrow. I think I may need to adjust the linkage/TPS, although the idle TPS reading was 1.02 volts, which is within the +/- .2 volts. I did not check the wide open throttle reading, but usually I found if I set the idle voltage good, the WOT was good also.

It's a bit late in this discussion, but I did want to share some historical info on this particular truck for those interested... aprox at 20k miles into this trucks life, the trans started "slipping"or hunting between gears. Dealer said nothing was wrong with it because the symptoms would not present itself when in for service. Every six months or so and sometimes on a rainy day, same thing.

Just by chance, I came to find a "sort of" solution...Just pop the hood, grab the main harness on the driver side of the engine, and give it a good shake...Fixed. Same fix when my complete set of gauges would "jump" or bounce and dash warning lights would flash in unison. Shake the harness, fixed for another six months. I tried many times to investigate the reason, but would never find out why, although I never completely opened up the harness.

I still don know why, but maybe this issue is by chance, part of the reason. Again, the dealership could never find the issue because no codes were present and the symptoms were not present when I waited the two weeks they needed for an appointment. Who knows, maybe in six moths I will know....

with all that said,
You guys have probably noticed I tend to think the worst, looking at all kinds of possibilities like bad PCM etc. I guess I just ask all kinds of questions as I go down the troubleshooting path. Please bear with me...Im still learning bit by bit even though I've been on this planet over 64 years!
As I do each repair on the truck, I pick up a better understanding of the many systems and how they interact and work together.

Thanks again for all your help and most importantly, your valuable time.

 

[DavidC]

Let us know when you finally find the culprit. Might be very valuable to someone in the future.

 

[Solar1]

Absolutely!

 

[Solar1]

So, the TPS trouble codes are gone and the TPS is adjusted perfectly to the service manual stated voltages. After one day of regular mixed driving (freeway/city) and all good, the trans is now acting a bit funky. No TPS codes and voltage good, but the trans overdrive is cutting in/out, and it feels like it is doing a bit of searching for a good place to shift.

The last thing I checked today before giving up for the day and getting in a the tub for a long soaking of the old bones, is the electrical connections at the trans. Speed sensor and the small harness of wires. Nothing remarkable as all lines appears solid and connected.

However, I did find something I believe was wrong.
I did do a quick visual check of the linkage and in particular, the trans throttle control or "detent" cable at the trans. (I looked at this close because I just installed a new cable at the time when I worked on the broke throttle linkage issue).

I found the black plastic "rod" looking sleeve that the cable goes thru loose. I was able to take the plastic rod thing and slide it back and "pop" in back into the molded recess opening. it seems to stay put.

so, my question is this: Since I know the cable has effect on the shift points, could it be that the plastic rod part loose was affecting the trans shifts to act erratic?
I have not yet taken it out for a test run after having popped that plastic rod back in place.

I including a photo to show the part I'm referring to.

 

[BigPapa]

That would be the TV (Throttle Valve) cable. If I remember correctly, make sure all floor mats and anything else under the pedal are removed. Get someone to push the pedal all the way to the floor while you check the cable at the transmission. you should be able to push the lever another 1/8" before the end of travel. This can be adjusted at the throttle end but it's tedious and lots of up and down from under the truck for you. We always just bent the bracket at the transmission just enough to get it right.

 

[Solar1]

Hey BigPapa, yes Throttle valve cable.
I never did any adjustment when I installed it as the trans shifted just fine when that was installed. I did not change the cable because the trans was shifting wrong; I just had noticed some wire cable fraying up at the throttle linkage attachment. im going to give the truck a run into town tomorrow and I will see if that plastic rod may have been binding up because of it being loose.

 

[Solar1]

OK folks, more info. Alright, I took another look at the Throttle Valve area on the trans this morning while she was warming up. Something I did not notice yesterday while inspecting (I'm embarrassed to say as it was right in front of me), I found a rubber vent hose that I assume was from the front differential (unless there is a transmission/transfer case vent) and it's mounting bracket laying right nestled in the Throttle Valve Cable attachment area.

It appears my wonderful transmission shop failed to remount the bracket when they installed the rebuilt trans a few years ago.
It must have been stuffed up in the area above the trans in order to get it out of the way while installing trans. While this is a totally separate issue from the TPS 5 volt power issue, it certainly added to my problems. Im guessing the bracket having been laying in the area of the Throttle Valve pivot must have caught the plastic rod of the cable and pooped it off. At least that is my guess.

After clearing that vent hose, I took the truck for a test run into town. The truck shifted perfectly normal, as did the overdrive.

Now, I don't want to get too excited yet, but I'm hoping this handles that overdrive issue. I'm keeping my fingers crossed.

 

[Solar1]

OK folks, more info. After many days of pulling my hair out, now I have another variation of the continuing symptoms with the overdrive issue.

the truck would be fine for a day or so and then act up again. I tried as best i could to check wiring and all seemed ok.

The truck continued to present erratic operation regarding the overdrive engagement.
As I had checked for trouble codes for several day and found no codes, I assumed all was good, so I did not check it again. That was a mistake.

Checking it a couple days ago, it once again had the PO123 code (high voltage at TPS). I checked the TPS with a voltmeter again and once again, the low (idle) and high (full throttle) readings were perfect.

However, when I moved the linkage to pull the throttle to full throttle, I thought I saw i bit of slop in the movement of the pivoting linkage and shaft into the TPS.
After closer attention, I moved the throttle linkage and felt for slop in the linkage. Sure enough the was a little.

Now, I had not considered this earlier, because I assumed the pivot linkage was good as I had rebuilt it with new (plastic) bushings 2 years ago. I hooked up an analog voltmeter and observed the readings as I articulated the throttle linkage to full throttle. I found that there was some erratic response in the TPS voltage. A few times the needle exceeded to high voltage limit as detailed in the service manual.

That certainly explains the trouble code.
So, I believe that just checking the high and low readings was not enough to show the issue until I moved the throttle linkage around. I can see that running down the road with engine and road vibrations, the TPS was giving offspec voltages.

I have ordered new bushings. In the meantime, I adjusted to linkage ever so slightly the opposite direct to account for the minor slop. Low and behold, the test drive and subsequent driving the last 2 days have shown no codes and that trans is acting absolutely fine and correct.
So, I will keep my fingers crossed and pay attention for codes and trans operation. As soon as the bushing arrive, I will rework the throttle pivot system and hope that this was the problem and it might now be resolved.

I will continue to update this thread after I install the bushings.

 

[DonFitzwater]

I highly recommend doing a tps delete. My last three 12 valve trucks have been deleted. Install a 5k linear potentiometer and set the voltage and forget about it. This will eliminate any tps and linkage potential of failure (considering your 5 volt circuit is solid and pcm are good).

 

[Solar1]

Hi Don, this is interesting....are you saying a fixed voltage is set on the pot, and the pcm does not need to see a varying voltage to shift or do the overdrive engage? what voltage do you set it at?

 

[DonFitzwater]

Hi Don, this is interesting....are you saying a fixed voltage is set on the pot, and the pcm does not need to see a varying voltage to shift or do the overdrive engage? what voltage do you set it at?

Yes, set the voltage and forget about it. The PCM isnt smart enough to need varying voltage. The torque converter will remain locked based on speed and or brake application to unlock. No idea what my voltage is set at.....I just adjust until it acts the way I want and then it's done.

 

[Solar1]

Thanks Don,
Had I known this as a solution, I would have tried it 16 years ago when I had to install the 1st of 3-4 TPS units, heck I don't remember how many Ive changed out in my truck. The dealer did the 1st one under warranty @ 50K miles.

So, the voltage is set for only the overdrive set point? (45-50 MPH)?

 

[DonFitzwater]

https://www.turbodieselregister.com/threads/t-p-s-delete-kit.239303/

 

[DonFitzwater]

I installed my delete kit and installed the potentiometer beside the OD on/off button on the dash in the hole where the fog light switch would normally live. I was going to install it on the knee bolster beside the trailer brake controller but didn't like the idea of a knob sticking out and maybe getting hit by me or another driver. I'll post some pics when I get time.

 

[Solar1]

Thanks for the link!

 

[Solar1]

Thanks for the TPS delete info. I may pursue this. In the meantime, I wanted to share the latest symptoms for you auto transmission guys to ponder and offer suggestions. After finding that I had loose linkage and correcting that, Im still experiencing weird symptom. The truck shifts excellent for about an hour of driving, including stop and go , and freeway driving, the truck will act up after slowing down below 45 mpm and drops out of 4th gear as normal. then, upon accelerating above 45 again, the trans will not shift to 4th as needed, sometime holding out until 55-60mph until upshift to 4th. It stays problematic like that until a complete engine cool down (not driving). Start up cold, truck shifts fine until warm up to normal operating temp (190-200) then act up again after an hour of of driving.


Now Im wonder again if there isn't a trans issue like overdrive solenoid seal or similar.
Trans temp sensor? Its only acting up after an hour of driving.

Im tired of guessing with this thing and I don't know how to further troubleshoot the darn thing

 

[Solar1]

Well Folks, the problem continues.
I continued to get TPS codes. I did have some slop in the throttle assemble.
I ordered some brass shaft bushings i found on ebay and they worked great for rebuiding the throttle assemble. Was finally able to properly adjust all the linkage rods and such.
Thought for sure that was it. No codes anymore.
after an hour of freeway driving (65-75mph) the same issue with the OD wandering in/out is happening. No codes and the TPS is set correctly.

I tried to adjust the trans throttle cable adjustment. (I dont have a clue how to do it correctly)
Immediately the truck was shifting absolutely fine.

3 days later, same issue creeps back.
Seeing as the cable came from the salvage yard (last summer) I was thinking I should just order a new cable an stop guessing if it is not stretched, so I did and have a new MOPAR cable waiting.

I have not yet installed the cable and was wondering what the procedure to adjust it is. I believe some chimed in here with that. The bigger question is should I even try to install/adjust it, or is it time to bring it to a "professional"?
Im not comfortable taking to a trans shop because thru the years (im an old guy) I have found their answer to every trans issue is "Complete rebuild"

I know at least once I paid for a trans rebuild that was not needed.
This was confirmed by a master mechanic.

The last shop that did that did a rebuild also rebuilt the transfer case...I found they did not tighten the front driveshaft CV yoke flange nut and it trashed the whole cardon cv unit. I have no confidence.

 

[DonFitzwater]

Have you verified the 5 volt reference signal from the pcm isn’t failing? You should spend some time verifying that AND you could also wire up a mystery switch and control od manually to verify the problem isn’t inside the trans.

 

[Solar1]

Hi Don, thanks, that is a good suggestion. Yes, I did confirm I have a good PCM 5 volt source.
I may have to wire in the switch like you said just to make sure the trans is not the issue.
Do you know the switch connection points?
Do I just tie in the switch at the tps terminals temporarily?