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Old 10-21-2021, 09:18 PM   #1
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Throttle Position Sensor for ISC

I just starting having an issue where if I have the engine brake on and it engages, it will not disengage (no throttle at all) until I come to a complete stop.
From what Iíve read, it sounds like my TPS (on the gas pedal) is not sending the signal to disengage the engage brake and allow the throttle to work when pressed, so the engine brake will not disengage until youíve reached a complete stop.
My question is, what is the correct TPS part number for the ISC? (The little part attached to the gas pedal with 2 screws.). When I Google ISC TPS, I get a million different results and when Iíve clicked on some, they are NOT for the ISC and I donít want to ďguessĒ.
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Old 10-21-2021, 09:54 PM   #2
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First, insure there is nothing preventing the pedal from fully returning to the idle position. The TPS may be tested with an ohmeter/ VOM. The actual readings are not as important as a smooth steady rise/decline from idle to WOT and back.
If the readins are erratic and jumpy the TPS is faulty.
Make sure all wiring connections are clean and tight, even on the compression brake controller.
If you determine the TPS requires replacement go to quickserve.cummins.com; register for the website then look up your part. You'll need your engine serial number to register.
I seem to remember this gets you a discount on parts too.
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Old 10-22-2021, 07:45 AM   #3
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The TPS will be specific to the throttle pedal manufacturer.

What RV do you have, you can put it in your signature.



Here is my throttle pedal parts page. The TPS is the small black piece mounted on the side. I can google the throttle pedal part number and then find the TPS, it's a ~$50 part. There are threads dealing with this if you do a search, I believe you can Ohm the sensor to see if it is working correctly.
Attached Files
File Type: pdf 1 Accelerator Pedal.pdf (37.1 KB, 7 views)
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Old 10-22-2021, 08:22 AM   #4
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Thanks guys.
Not sure what happened to my signature.
Itís a 2002 HR Scepter with the ISC.

I may just have to pull it off and see if thereís any info on it.
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Old 10-22-2021, 11:42 AM   #5
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My understanding is that the peddle position sensor signal is used to trigger the exhaust or engine brake whenever the peddle is at idle (zero pedal). The engine or tranny computer then disengages the brake when the engine rpms drop below some pre-programmed threshold. I think it was about 1200 rpms on mine. It was the rpms, not the throttle position. That's the way Freightliner explained it to me on my Cummins ISL with it's internal Jake. Other systems may well differ, either by design of programming.


The Jake disengaged if any pedal was applied at all - as soon as the peddle went off the zero (idle) position, the Jake deactivated deactivated. Even if the rpms were high and I was screaming downhill.
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Old 10-25-2021, 07:24 PM   #6
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Quote:
Originally Posted by Gary RVRoamer View Post
My understanding is that the peddle position sensor signal is used to trigger the exhaust or engine brake whenever the peddle is at idle (zero pedal). The engine or tranny computer then disengages the brake when the engine rpms drop below some pre-programmed threshold. I think it was about 1200 rpms on mine. It was the rpms, not the throttle position. That's the way Freightliner explained it to me on my Cummins ISL with it's internal Jake. Other systems may well differ, either by design of programming.


The Jake disengaged if any pedal was applied at all - as soon as the peddle went off the zero (idle) position, the Jake deactivated deactivated. Even if the rpms were high and I was screaming downhill.
The last part of your post is how it's supposed to work.
If the switch is on then the brake will engage when at no throttle, and disengage as soon as any throttle input is detected.
Mine is engaging properly, whatever is suppose to make it disengage when the throttle is pressed is not happening.

I did figure out that if I let the brake engage, then turn the switch off AND press the brake pedal once, the brake will disengage like it's supposed to, so at least I've got use of it if needed, but that's a lot of pain in @ss steps to be able to use it.
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Old 10-25-2021, 07:29 PM   #7
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I pulled the entire pedal assembly off tonight and all I can find is that it's a Williams Controls pedal assembly, but no part numbers on the pedal assembly at all. When I took off the TPS sensor itself, it has 131856 on it, but I'm not getting anywhere Googling that. (At least nothing that looks like mine.)

I know I've seen some other threads on here that I'll have to search for again that mention Williams Controls, so I'll look back again, but if the above info gives anyone what they need to possibly provide a link, PLEASE do.
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Old 10-25-2021, 07:39 PM   #8
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During your web searches did you find and peruse this website:? https://www.throttlecontrol.com/p-11...-controls.aspx
Thanks, but I have no idea what any of the ones are in the link or how they compare to what I've got. With no pictures and none of them referencing the part number I've been able to find on mine, I'm completely in the dark.
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Old 10-25-2021, 07:50 PM   #9
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Have you signed up for parts.cummins.com and looked up the TPS by your engine serial number?
Also look at Quickserve.cummins.com it also requires a sign-in and your engine serial number.
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