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Old 08-14-2023, 11:42 PM   #1
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T444e Throttle Gas Pedal / Electrical Problem Question

Hello,
I have an issue with my gas pedal on a T444e. A mechanic friend for regular cars was inspecting it today and returning Wednesday to complete the solution.

The issue is that the throttle was unresponsive to being pressed. After he tinkered with some wires, it now works at 50% capacity. But it LOSES ALL POWER to the throttle (and warn engine flashes) after going approximately past 50% depth on the pedal. We are both unsure why this is happening. Any ideas?

The 5V reference may be reading low. And the 12V signal was weak at first, so he cut the wire which literally restored 50% power back to the initially broken pedal, wirelessly...

All 5 wires are attached right now but potentially those two reading incorrectly. We plan to rewire the entire 5 wires from the throttle position sensor to the ECM on Wednesday. The concern is that there is still a loss of all power to the pedal after it goes past 50-70%. Hopefully 5 new wires just solves the problem, but if not, I'm wondering where we should be looking next. He mentioned something about the 'Throttle Body' supplying air to the engine or something like that lol.. But he couldn't locate it on the bus because he's used to cars. Where's that thingy?

Any advice on solving this problem in general would be amazingly helpful. Maybe the biggest headache in my life right now. Haha. Thanks!

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Old 08-15-2023, 09:41 AM   #2
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I'm not a diesel mechanic, but I am (or rather was) a mechanic in another life, and your description of events leads me to believe your friend - however good-intended - doesn't really know what he's doing in this context. I'd find someone more qualified before you spend a lot of time & effort making things worse rather than better.
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Old 08-15-2023, 05:29 PM   #3
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ugh!!! cutting wires!!



the wires on that pedal have different functions... the pedal has a couple different functions within it.. there is the 0-5 volt signal which tells the computer the throttle position.. that uses 3 of the wires.. reference 5 volts.. ground.. and signal.. the signal wire changes based on the pedal position.. the ground is reference ground back to the ECM.. the 5 volts is the supply voltage sent down.. you only ever test computer voltages against the supplied reference ground (not the frame of the bus)..


the other 2 wires are the idle position switch... this is a backup of sorts... if the TPS goes bonkers and you let off the pedal.. the pedal returns to "home" and the switch closes to the ECM letting it know the pedal is not pressed..



if you press the pedfal and that switch doesnt indicate the opedal is being pressed then the ECM will not read the actual position..



by cutting various wires you likely have faked it into believing things that arent true..and thus restored some ability for the pedal to be read.. voltages float through resistances.. pullup resistors sent through other resistances and a floated ground result in erratic but some ranmge of voltage..



I am on a biz trip and dont have my set of service books with me but it wouldnt be the first time ive seen a bad pedal assembly cause issues... .. more often than the wiring unless the contacts are corroded from road salt and such..
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Old 02-24-2024, 01:41 PM   #4
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Talking Any chance you can layout steps to diagnose? Or a source to purchase new assemblly

This post is extremely helpful and gives me a good starting point. What would you recommend as a first step for people having this issue? Cut the wires 1x1, strip new section and reattach? Then purchase new assembly if it's not resolved? Or could you talk about how to diagnose the wires?





Quote:
Originally Posted by cadillackid View Post
ugh!!! cutting wires!!



the wires on that pedal have different functions... the pedal has a couple different functions within it.. there is the 0-5 volt signal which tells the computer the throttle position.. that uses 3 of the wires.. reference 5 volts.. ground.. and signal.. the signal wire changes based on the pedal position.. the ground is reference ground back to the ECM.. the 5 volts is the supply voltage sent down.. you only ever test computer voltages against the supplied reference ground (not the frame of the bus)..


the other 2 wires are the idle position switch... this is a backup of sorts... if the TPS goes bonkers and you let off the pedal.. the pedal returns to "home" and the switch closes to the ECM letting it know the pedal is not pressed..



if you press the pedfal and that switch doesnt indicate the opedal is being pressed then the ECM will not read the actual position..



by cutting various wires you likely have faked it into believing things that arent true..and thus restored some ability for the pedal to be read.. voltages float through resistances.. pullup resistors sent through other resistances and a floated ground result in erratic but some ranmge of voltage..



I am on a biz trip and dont have my set of service books with me but it wouldnt be the first time ive seen a bad pedal assembly cause issues... .. more often than the wiring unless the contacts are corroded from road salt and such..
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Old 02-24-2024, 01:47 PM   #5
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Quote:
Originally Posted by GreenGo View Post
This post is extremely helpful and gives me a good starting point. What would you recommend as a first step for people having this issue? Cut the wires 1x1, strip new section and reattach? Then purchase new assembly if it's not resolved? Or could you talk about how to diagnose the wires?
I really don't understand how you say this post is helpful when you don't even describe the issues you are having.

Pedal not responding ???

Try reading this thread for more info.
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Old 02-24-2024, 03:28 PM   #6
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The issue I'm having is already described in this thread (same issue). I'm new to forums and meant to address my question in response to cadillackid
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Old 02-24-2024, 04:13 PM   #7
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Solution

Hey, I've seen others run into the same issue so I should probably post my solution...

I ended up buying the wiring assembly on amazon. It included the adapter for all 5 wires to plug in to the female adapter.

I am describing it poorly because some time has passed, and I can't find the amazon link for what I purchased, otherwise I would share that directly.

But basically I bought SOMETHING LIKE THIS: https://www.amazon.ca/Dorman-904-769...df9fb1546d3c50

That probably isn't the correct one for your bus or mine - but it's the closest picture I can find right now. It obviously needs to be compatible with your gas pedal & vehicle.

But the point is, replacing the full TPS and 5 wires, to connect to a healthy set of original wires from the bus resolved my issue. I think my problem was some water damage that got onto the TPS and ruined something.

When I switched just the TPSn out it didn't fix it, but when I basically refreshed the first few feet of wires coming off the TPS, including the adapter, it was solved.

Hope that helps.
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Old 02-24-2024, 05:32 PM   #8
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Originally Posted by GreenGo View Post
The issue I'm having is already described in this thread (same issue). I'm new to forums and meant to address my question in response to cadillackid
Ok new guy...welcome to the madness!

cutting wires as was suggested in the first post...well the response in the second post sums it up...not the right way or good way to address this issue.

Cadillackid explains real well what is occurring within the circuit now you have to find a way to understand it. It is quite simple indeed.

If you go to post #11 in this thread and print out the pedal circuit diagram you will better understand what Cadillackid is explaining.
Post #17 also has more good info and a sheet for diagnostics on the TPS.

There are 5 wires and two circuits involved, all contained within the sensor on the pedal, where the 5 wires go to.

Cutting those first three wires is useless as it takes away the control circuit for the ECM to follow/understand.

The second set of two wires is your idle circuit control.

That sensor does go bad, mine did and that is how I learned, with the help of cadillackid, how it works and how to repair it.

the sensor cannot be tested reliably with a multimeter as those circuits now contain a hall effect sensor within. You will need an oscilliscope to see the hall effect work or not work.

The real simple solution and easiest thing to do is to first replace the sensor. You can also use a voltmeter to make sure your 12v and 5 volts are in fact present on the wires.

DO NOT CUT ANY WIRES at this point in time!

replace the sensor and test drive the bus!
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Old 02-24-2024, 08:21 PM   #9
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Thanks so much for the detailed info. I read through that entire thread and have the diagram saved. I'm a bit stuck on making sure I'm grabbing the correct sensor replacement. I looked online and there are a bunch of suggestions. How did you determine which sensor you needed? Was it identified anywhere? I could only find "0121" labeled where the wiring is inserted.
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Old 02-24-2024, 09:07 PM   #10
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Originally Posted by GreenGo View Post
Thanks so much for the detailed info. I read through that entire thread and have the diagram saved. I'm a bit stuck on making sure I'm grabbing the correct sensor replacement. I looked online and there are a bunch of suggestions. How did you determine which sensor you needed? Was it identified anywhere? I could only find "0121" labeled where the wiring is inserted.
I could find no guide or manual for a specific part number.
If you go to the dealer they will give you a part number. I did that. Also my sensor had a part number on it.

In the end, after alot of googling, i kinda based my final decision on a part number after basically looking on ebay and also ali babba and made a wild educated guess.

In that thread you will see where i bought it from a parts house in Florida. It was cheap and confirmed it works just fine .
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Old 02-25-2024, 07:25 AM   #11
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my bus is a T444E, this is the IH part number listed for the TPS sensor..



on the IH original throttle pedal assemblies the TPS is a separate service part from, the whole pedal assembly.. I have zero idea on the aftermarkets..



I did a quick link search for the TPS that the IH book lists to fit *my* bus.. which is a 2000 T444E, your 2001 DT466E is likely similar..



to look for IH part numbers for your VIN you can sign up for a Free account on Repairlink, and set up with a local IH dealer to get parts and prices (yes the prices are high because no discounts are applied) you can get IH part numbers then cross reference them online to aftermarket parts..


https://advancetruckpartsusa.com/pro...QaAj07EALw_wcB


thats a link to the one designed to fit mine..



I know a lot of people seem to buy the whole pedal assembly and end up with a dorman brand.. my personal opinion of dorman is not great... ive had issues...



my post with the how it works is there simply because I tend to test [arts befopre replacing them.. and how the system works to get you a better understanding of why it might fail..



electronics can be a rabbit hole of just parts-canon style repair which results in tons of costs..


learn how it works and you can better troubleshoot issues..
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Old 02-25-2024, 10:39 AM   #12
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@GreenGo,

Take a look at this ebay listing.
https://www.ebay.com/itm/124918752514

Also take a look at the bottom of the listing that shows the compatibility listing.

At those prices, 24 bucks, I would buy 2 of them, one for a spare...you never know when things go bad!

also, before you purchase one, confirm your unit and the one your buying are 5 wires. some of these come in 6 wire so just make sure you check.
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Old 02-25-2024, 08:46 PM   #13
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A dead spot in the tps can cause a completly dead pedal. Chopping wires is hack. Dont do it. Unplug and test.

Like others said, purchase the sensor first.

If you had a scanner you could see the idle validation switch opening and closing. You can also see what your tps is reading as well. Save some pennies and look at purchasing something to scan
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