Throttle Position Sensor Problems - Solving them.

[Rawze]

{This is a re-post from the old forum from Feb. 2015} ...

Well, I had a Pete 387 truck over here for some tune-up work, and It had the same error codes that some of you on the forum have said they have seen. It also had Intermittent Turbo Actuator alarms too. This guy has had this truck looked at 8 times for the Accelerator and turbo, had the wiring harness changed by the dealer 2 times, the throttle control module changed 3 times, and they even did software updates and re-flashes to the ECM to try to solve it. He was at his wits end with it and was seriously frustrated. His ECM was already replaced once before for this, and the dealer told him that it could only likely be the ECM again.

Among other problems, he keeps having TPS (throttle position sensor) issues and failures.

This is what I found... FIRST of all,... his truck is getting old, and the wiring harness are very dusty and dirty in general. Here is the procedure I used to find the problem(s)...

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** I suspected it was an intermittent problem, so here is how I searched for that...
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I hooked up computer and had him turn his key-switch on. I then made a graphics screen and monitored parameter 'Accel_Position_Sensor_Volts' (in calterm software). I edited the plot on the graph, so that it had a scale of 0 - 5 instead of 0 - 100. With the pedal at rest, it read about 1.03 volts, and when the pedal was all the way down, (in the ecm) the parameter read 4.19 volts. It also responded without any sudden jumps when pressed slowly from min to max and back several times even while wiggling the pedal sideways and yanking on wires.

I then put a block of wood under the pedal and a brick I had on top of it. This put it in about the mid-way position and It read something like 3.23 volts I think. We then proceeded to wiggle and yank EVERY harness for the engine and pedal hard,... very hard. We also shook the cab of the truck, and shook all the connectors, even the one for the ECM. The voltage didn't jump, but held steady. It didn't seem an intermittent wiring problem, so I moved on...


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I suspected the Supply voltage that feeds the Throttle Control Module on the the pedal...
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I went and got the wiring diagram for the truck, and found out that from the ECM, the supply voltage comes from a pin labeled "Sensor Supply 5", and is one of many 5 volt supply lines to the various sensors. This particular pin supplies voltage, on the Pete 387 to the throttle control module, the Coolant Level Sensor AND to the tail-shaft speed sensor. This means that if the wiring to/from or if one of these other sensors was bad then it could effect the supply voltage and throw off the pedal sensor too.

I unplugged the connector for the Throttle Control Module, and checked pins 'D' and 'F' on its plug. This was the 5-Volt and ground connection. It read 4.87 Volts (on a volt meter)... I then proceeded to disconnect the Coolant temp sensor, and watched for the supply voltage to change,... It did not. I did the same for the Tail-shaft sensor, and it held steady as well. This eliminated the possibility other sensors shorting it out and we wiggled the harness going to the tail sensor as well.. Still no results...


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I next, suspected tarnished pins on the plugs to the ECM and/or the CAB, or other pigtails...
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I pulled the pigtail plugs apart under the dash from the throttle pedal cable that had been replaced recently,... all the pins looked new and good. Next I pulled BOTH the main cab plugs at the firewall and guess what ...

   



The Upper one had what looked like a slight condensation of moisture in it. Not a lot but a tiny bit all around the rubber edges inside it. The pins were also slightly (very slightly) darker in color that they should have been. I got some Brake Cleaner and sprayed the plug (both ends) well. i followed it up by flooding them heavily, soaking the insides of the plugs with Brake Line Anti-freeze (pure Methanol). This will displace ALL the moisture from these plugs. I then re-seated them about 10 times on and off to polish the contact surfaces a little and seated them well. I did not use WD-40 because I wanted a dry, oil-free connection when I got done.

Next I went to the ECM plug (black one). I pulled it off and found a bit of actual Dried MUD in it around the edges. About half the pins were tarnished slightly so I flushed it using the same procedure. I re-seated it about 4 or 5 times to polish the contacts then secured it tightly.


I was then informed that the truck Owner had the engine washed regularly whenever the truck is washed,.... NEVER DO THIS!!!!!!!!,... It pushes WATER up into the plugs and connectors. If there is heavy salt on the motor, just lightly rinse it, nothing more. NEVER use a pressure washer on or around the wiring!!!.


After we got it back together,... all his problems INCLUDING the TURBO ACTUATOR ALARMS,.. ALL went away and have never come back. - You had better believe he doesn't let anyone wash under his hood with a power washer any more either.

{2021: just as a follow-up, 5 years later... he still had not had any more TPS sensor problems}.


Here is some other places the wiring likes to go bad on those pete's and KW's.
http://rawze.com/forums/showthread.php?t...05#pid3505

[cspence478]

Wow! It’s very identical to my situation. And I do engine washes. Which I will stop. But that makes a lot of sense. Thanks will do and let you know. Thanks!!

[cspence478]

Hey I did the cleaning. Will let you know in a month how it goes.

[Chamberpains]

Im currently chasing a TPS sensor rapidly and very intermittently losing an unknown and non steady amount of counts on my cm870 International 9400i with no check engine lights and no codes recorded. It causes a very slight but somtimes very noticeable stutter when accelerating or maintaining speed while rolling down the road especially when it's cool after 1st start up of the day. I've so far replaced one whole full throttle pedal assembly (it was pretty whooped with 1.2mil miles), cleaned and checked all connectors under the hood, yanked, twisted, shook, bounced and waltzed with every harness I can get my hands on. I've ohmed and tested the circuits according to Insite troubleshooting trees and still its occuring only when the truck sits turned off for longer than 8hrs or cools down completely and then it clears up ALMOST completely but not always completely about 30 minutes in to pulling down the road. After it warms up or has taken some bumps. I've only caught it by monitoring TPS voltage and position with Insite while going down the road.
   
I currently have an ECM ordered so I'll see in about a week if this'll get it cured. The ECM on the truck is original and is 13 years old so it's about time to hang a new one any way. I'll update when I finally get this squared away.

[Rawze]

(08-12-2018 )Chamberpains Wrote:  ...
The ECM on the truck is original and is 13 years old so it's about time to hang a new one any way. I'll update when I finally get this squared away.

The expected lifespan on most of the electronic components inside an ECM is about 8 years. If you replace the ECM as a step to solve it, it is older than that, and it does not fix it, you have lost no money in doing so.

Hang onto the old one until you are certain. If the new ECM does not solve anything, keep the new one on there and also keep the old one as a spare.

[Kid Rock]

(08-12-2018 )Chamberpains Wrote:  Im currently chasing a TPS sensor rapidly and very intermittently losing an unknown and non steady amount of counts on my cm870 International 9400i with no check engine lights and no codes recorded. It causes a very slight but somtimes very noticeable stutter when accelerating or maintaining speed while rolling down the road especially when it's cool after 1st start up of the day. I've so far replaced one whole full throttle pedal assembly (it was pretty whooped with 1.2mil miles), cleaned and checked all connectors under the hood, yanked, twisted, shook, bounced and waltzed with every harness I can get my hands on. I've ohmed and tested the circuits according to Insite troubleshooting trees and still its occuring only when the truck sits turned off for longer than 8hrs or cools down completely and then it clears up ALMOST completely but not always completely about 30 minutes in to pulling down the road. After it warms up or has taken some bumps. I've only caught it by monitoring TPS voltage and position with Insite while going down the road.

I currently have an ECM ordered so I'll see in about a week if this'll get it cured. The ECM on the truck is original and is 13 years old so it's about time to hang a new one any way. I'll update when I finally get this squared away.

Just a thought here; but recently when researching a way to fix the abs issue I’ve had, I read an article they may have some merit to it.

It said the voltage in the abs system is so low that if one were to make a splice or wire repair in its circuit, that a crimp/butt connector would cause to much of a voltage drop and cause low voltage problems eventually; and that all wire repair on abs circuits must be soldered! ... which makes a lot of since on mine, I’ve spliced into one of my abs harness’ about a year ago in response to a low voltage / short to ground code. I spliced in a few butt connectors where i was suspicious of wire condition. Here we are a year later getting the same code, after checking wheel end play,and new sensor. So I’ll be pulling the harness and learning to solder

[dhirocz]

I was taught that all wire repairs should be soldered with a linesman's knot and heat shrinked at a minimum, with adhesive heat shrink used on exterior connections. Butt connectors should be used just to get you from point A to B for a proper repair. I don't see it being much better than twisting together a wire and covering it with electrical tape.

Butt connectors are not sealed connections, can play hell with resistance sensitive circuits, and sometimes come loose due to vibration. They also invite corrosion.

[Rawze]

when my drive-shaft failed, it ripped all the wiring and air lines out of the back end of the truck. I just re-made all the harnesses myself with wire from home depot and replaced all the plugs with standard automotive plugs purchased off of amazon.

reference: http://rawze.com/forums/showthread.php?t...1#pid16511

For the ABS, I got some 100-ft spools of wire, put one end of them in a drill and stretched out the other end and spun them together to make the twisted ABS wires up. I soldered all the connections to the pins in plugs I made up and sealed all the ends of the plugs with extra silicone.

I got new split-loom and put on all the wiring harnesses I re-made and re-installed everything.

-- I have never had an issue with it and it looks exactly like it came from the factory. The THHN wire I used was better quality than what came out.

Patching a headlight or marker light wire is one thing but if I had an ABS wire rub in half on me, I would pull the wires out of the plug with a pin remover, make a harness up, and replace the whole thing to where it went.

[Chamberpains]

(08-13-2018 )Kid Rock Wrote:  Just a thought here; but recently when researching a way to fix the abs issue I’ve had, I read an article they may have some merit to it.

It said the voltage in the abs system is so low that if one were to make a splice or wire repair in its circuit, that a crimp/butt connector would cause to much of a voltage drop and cause low voltage problems eventually; and that all wire repair on abs circuits must be soldered! ... which makes a lot of since on mine, I’ve spliced into one of my abs harness’ about a year ago in response to a low voltage / short to ground code. I spliced in a few butt connectors where i was suspicious of wire condition. Here we are a year later getting the same code, after checking wheel end play,and new sensor. So I’ll be pulling the harness and learning to solder

You got me thinking... I did just repair some rubbed wires on the back of the engine and with the monitoring of the voltage i know I'm working with a circuit that is operating at .45 volts with the peddle released and builds to 3.66 volts all the way to the floor. So what you say makes sense. Looks like I'll be also pulling the dog box to see which wires I repaired. Hopefully it is the problem and all I have to do is replace a wire.

Rawze you're spot on with my thinking. The ECM I got off ebay doesn't require core except for warranty to be valid. So I have no problem keeping the old one.