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