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Old 04-02-2018, 09:04 AM   #1
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Throttle Position Sensor Fault (TPS)

I have an intermittent TPS fault that I'd like to chase down. I've seen several other threads here which sound similar, but haven't seen a definitive fix for the issue.

When this happens, the engine will idle, but the throttle pedal has no effect on engine speed. If you're already moving, you can accelerate or coast using the cruise control.

The dash WARNING light illuminates and my ScangaugeD throws a 91 13 XX code, the XX being the number of times the fault has occurred. Ninety one is the SAE J1939 Protocol Suspect Part Number (SPN) which indicates the area of the fault and the 13 is the SAE J1939 Protocol Failure Mode Identifier (FMI).

The SPN code 91 is the "Accelerator Pedal Position 1" and FMI 13 is "Out of Calibration" It also equates to Cummins trouble code 131 which I've attached. Cummins doesn't mention FMI 13

I've also found information that says the "newer" TPS has two throttle sensors in the TPS while "older" units have a TPS and idle validation circuit. I haven't found anything which defines newer or older. I'm thinking a 2000, which is pretty close to the time when the electronic engines were first deployed, is probably an older unit.

The TPS circuit contains three components, a +5 volts, a return ground and signal wire. The +5 volts and return ground originate in the ECM and the throttle signal originates at the TPS. I've included a pin out in the attachments.

I've also attached a pretty good picture of the TPS circuit although the accelerator pedal is a different model than I have on my coach. All six wires, three for the TPS and three for the idle validation circuit, are in one connector on my Dynasty while the picture shows two different connectors.


I've looked at different troubleshooting guides and found different possibilities for the problem.

The TPS is bad
TPS is out of caliberation
Fault in idle validation circuit
Bad connection between the TPS and wiring harness
Bad connection between wiring harness and ECM
Faulty wiring between TPMS and ECM

One of the steps Cummins says to take is to replace the three wires between the TPS and the ECM to see if the problem goes away. If it does, then it says to replace the wiring harness. (not going to happen)

Other information I've gleaned from the internet:

The TPS wires must be electronically isolated from the other wires in the OEM harness and should be a twisted triplet, twisted at a rate of one inch per twist.

The connections for the idle validation switch are made through the OEM harness connector B. The normally open contact (at idle position) is connected to Pin B25. The normally closed contact (at idle position) is connected to Pin B26.

Here's my assumptions.

My TPS is operating correctly, it was replaced a little over two years ago by the PO of my coach to address the issues I'm still having. He'd been experiencing them for a few months and took the coach to Cummins to diagnose. They pulled the code and replaced the TPS and the issue went away for about a year.

The ECM is working correctly. Its unlikely the ECM has failed in any way since everything else seems to be working fine.

The issue is probably a connection between the ECM and the TPS, although the ground for the idle validation circuit seems to be separate from the ground supplied by the ECM for the TPMS.

So far I've disconnected the TPS connector at the pedal and applied dielectric grease. The design of that connector makes cleaning any individual pins problematic since they are very small and enclosed in the male connector. One thing I noticed was the twisted wires from the TPS are bundled with the three wires from the idle validation circuit and then bundled with a bunch of other wires in the harness and tie wrapped together before they exit through the fire wall. There is a lot of excess wire there and I'm going to un-bundle them and separate the TPS wires from the main bundle as specified in the Cummins literature.

I'd be happy to have anyone with any ideas chime in.
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Old 04-09-2018, 07:59 PM   #2
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Dennis, several of the procedures for checking and troubleshooting are a great deal more difficult than simply replacing the TPS. When I bought my coach in April 2013, the TPS had just been replaced days before.

A few months ago, I began having problems. My symptoms were erratic (usually higher) idle, and transmission shifts that differed from what was "normal".

I replaced the TPS again a few months ago, and it solved the problems. Williams Controls Part Number 131507. $65 from most heavy truck parts dealers. I'm ordering another one for a spare.
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Old 04-10-2018, 06:41 AM   #3
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Quote:
Originally Posted by Vanwill View Post
Dennis, several of the procedures for checking and troubleshooting are a great deal more difficult than simply replacing the TPS. When I bought my coach in April 2013, the TPS had just been replaced days before.

A few months ago, I began having problems. My symptoms were erratic (usually higher) idle, and transmission shifts that differed from what was "normal".

I replaced the TPS again a few months ago, and it solved the problems. Williams Controls Part Number 131507. $65 from most heavy truck parts dealers. I'm ordering another one for a spare.
Thanks Van, replacing the TPS is the last thing on my list as I go through the circuit from the front to the back of the coach. I figure I ought to give checking the connections a try first.

The TPS on my coach doesn't look like the one on yours.

Williams 131490 Throttle Position Sensor





Williams Controls Part Number 131507



I can buy the International Harverster version of Williams 131490 on e-bay for $29.

https://www.ebay.com/itm/INTERNATION...FXPCND&vxp=mtr
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Old 04-10-2018, 10:15 AM   #4
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Cummins went from the C8.3 mechanical injected engine to the ISC electronically controlled engine in 1998. But the older C8.3 engines still used an electronically controlled throttle in RV applications.

I think you are on the right track separating the twisted wires. Also try to separate them from any high voltage wire that may induce interference or noise in the low voltage TPS system. Unfotunately, there probably is a high voltage line somewhere close to your TPS wires in the long run back to the engine. This may be impossible to locate.

Also, many times just changing the TPS will stop the issue. I know it's a pain, but if you keep two TPS parts on hand you can just swap them and the problem usually goes away for a while.
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Old 04-11-2018, 06:38 AM   #5
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Quote:
Originally Posted by vito.a View Post
Cummins went from the C8.3 mechanical injected engine to the ISC electronically controlled engine in 1998. But the older C8.3 engines still used an electronically controlled throttle in RV applications.

I think you are on the right track separating the twisted wires. Also try to separate them from any high voltage wire that may induce interference or noise in the low voltage TPS system. Unfotunately, there probably is a high voltage line somewhere close to your TPS wires in the long run back to the engine. This may be impossible to locate.

Also, many times just changing the TPS will stop the issue. I know it's a pain, but if you keep two TPS parts on hand you can just swap them and the problem usually goes away for a while.
I haven't had a chance to pick up the flexible conduit in the small size I need for 3 wires. Once I do that I'll continue checking connections back to the ECM, then see how things go. The problem is, the TPS error only happens occasionally. It happened once in a 500 mile trip, then three times in a hundred miles then nothing for another 600 miles.
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Old 04-11-2018, 08:47 AM   #6
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First off I will say I don’t speak compression Ignition engines nor claim to.

That being said here I go and sure I will stick my foot in my mouth.


Without checking for the most current calibration update as seen here and stated from Cummins you could be chasing a ghost and something that you may never catch because there is no physical issue with any of the components and the update has to do with some parameters in the programming that need to be changed a bit by re-programming it …that’s is not uncommon in LD trucks and cars.Click image for larger version

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So if I now know that the ecm has the most current updates, I am going to GUESS because that is all we can do at this point with no data or diagnostic equipment.

I would be paying very close attention to circuit 29-30 at the ecm.
As stated in the enable criteria to set the code the ecm is seeing above +4.55

I would be willing to be that the ecm is NOT seeing 12vdc causing the fault code ( that is very rare in anything I have been involved in) but rather that the voltage it’s reading when this fault happens is somewhere in the area just above 5vdc and if so there is a a pretty good chance that it’s in the return circuit.
Most scanners will lock in on the data and store it when the fault codes sets and you can then look at the recorded data when it set the fault code …if you had this you would know what the reference voltage jumped too and leading you to a logical diagnostic path.

1. You need to know if you have the most recent calibration update


2. Without a scanner that can give you some live data you will most likely need a multi-trace lab scope so that you can monitor the live voltage on more than one channel at a time …a digital DVOM in most cases is to slow to catch the glitch … but if bad the drop out is bad enough it may. You may need a lab scope either way IMO.

3. If you have access to a lab scope you can do a sweep test of the TPS sensors and if so do both the old and new TPS sensors again a DVM will be too slow IMC ( FYI It’s not uncommon for TPS sensors to have carbon tracking issues due to wear)

If you monitor the ref voltage # 19 and open the return signal wire itself you will see the jump in reference voltage on # 29 and that I believe is what the ecm is seeing to set the fault 131 and not a short to 12vdc ( Just guess)

I probably made no sense…. but I tried.

Guess 1. Carbon tracking issues with the TPS and can be caught with a lab scope

Guess 2 again and NOT a calibration update issue? I would have my nose all over that return signal circuit starting both at the TPS pin terminals and the ECM pin terminals checking both very carefully with a flashlight and a magnifying glass and at this point.

I would be using Stabliant 22 on the pins and not dielectric grease

https://www.amazon.com/Stabilant-5ml.../dp/B001E50GQS yea I know... some pretty pricey stuff.


So what I was trying to say is that if had access to a multi-trace lab scope I would monitor all three circuits at the same time 19-30-29 at the ecm and shake rattle and pull that harness and all related connectors six ways from Sunday while monitoring and recorded the voltage

Intermittent failures in low voltage circuits ..Yikes

Just a wild &*^ Guess .... Happy Hunting.



As I go back to the cheap seats in cyberspace feeing you pain an thinking to myself ….what about the possibility a stray excessive AC voltage issue

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Old 04-11-2018, 11:53 AM   #7
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Rob,

I don't think my coach has had the ECM updated in many, many years so I have an appointment at the local Freightliner shop to do just that at the end of the month.

In the meantime, I'm going to do my best to make sure all the connections are secure and the wires are run like they are supposed to.

Checking voltages on lines with an o-scope is theoretically possible because I have a four channel digital 100 MHZ oscope. The issue would be figuring out how to sample the signals. That'd be a last resort for me.
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Old 04-11-2018, 02:15 PM   #8
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Rob,

I don't think my coach has had the ECM updated in many, many years so I have an appointment at the local Freightliner shop to do just that at the end of the month.

In the meantime, I'm going to do my best to make sure all the connections are secure and the wires are run like they are supposed to.

Checking voltages on lines with an o-scope is theoretically possible because I have a four channel digital 100 MHZ oscope. The issue would be figuring out how to sample the signals. That'd be a last resort for me.
Most reflash calibrations updates that I worked with, the OEM would call for the current calibration number and then show if there were any updates and what issues were addressed in those updates.

That being said I have seen calibration updates ( reflash) that had nothing to do with the particular issue that I was chasing.....yet still fix them ...not trying to sell you on a reflash (lol) ....just telling you what I have seen in the past.

The situation you are in has to be very frustrating

Happy Hunting
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Old 04-12-2018, 06:27 AM   #9
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Originally Posted by barmcd View Post
I haven't had a chance to pick up the flexible conduit in the small size I need for 3 wires. Once I do that I'll continue checking connections back to the ECM, then see how things go. The problem is, the TPS error only happens occasionally. It happened once in a 500 mile trip, then three times in a hundred miles then nothing for another 600 miles.
Dennis,

Do as Van says and just replace the TPS. The old style TPS is based on a carbon wiper resistor that wears with use. Judging from your photo you are old enough to remember the old volume controls on stereos that would have a scratchy position. They were also based on a carbon wiper resistor and the only cure was to replace the control. You could spray it with contact cleaner and it would improve for awhile but the problem would soon return. Your TPS is just like your brakes and is a wear item. Back when automobiles had the old throttle body fuel injection I had to replace several of the TPS sensors.

Bob
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Old 04-12-2018, 06:44 AM   #10
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Dennis,

Do as Van says and just replace the TPS. The old style TPS is based on a carbon wiper resistor that wears with use. Judging from your photo you are old enough to remember the old volume controls on stereos that would have a scratchy position. They were also based on a carbon wiper resistor and the only cure was to replace the control. You could spray it with contact cleaner and it would improve for awhile but the problem would soon return. Your TPS is just like your brakes and is a wear item. Back when automobiles had the old throttle body fuel injection I had to replace several of the TPS sensors.

Bob
Bob, it was changed in 2016 by a Cummins shop and only has about 12,000 miles on it. That's why I'm fixing the wire routing and checking connectors first.
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Old 04-12-2018, 05:59 PM   #11
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Dennis, my TPS had been replaced just before I bought it about five years ago. As Bob said, it may have ORIGINALLY been a potentiometer-type with wiper on a carbon track when it was built in 1999. But the one I replaced was a Hall-effect device, and still it went bad in five years, 60,000 miles. I'm really surprised yours is an IH-type part, but I would bet it is also a Hall-effect device. I admire your tenacity in wanting to know "why" instead of just fixing it. Engineers like Bob and me fall into that trap frequently. But I still think you'll find replacing the TPS will fix the problem. I vaguely remember when ordering the part that somewhere there was a warning NOT to use an IH part as a replacement. Sorry, I don't remember the reason why.

Good luck, my Brother! You have become a very savvy tech in a VERY short time.
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Old 04-12-2018, 06:33 PM   #12
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Dennis,

Do as Van says and just replace the TPS. The old style TPS is based on a carbon wiper resistor that wears with use. Judging from your photo you are old enough to remember the old volume controls on stereos that would have a scratchy position. They were also based on a carbon wiper resistor and the only cure was to replace the control. You could spray it with contact cleaner and it would improve for awhile but the problem would soon return. Your TPS is just like your brakes and is a wear item. Back when automobiles had the old throttle body fuel injection I had to replace several of the TPS sensors.

Bob


and they love to carbon track and skew the TPS voltage or go open for a split second setting fault codes....... in most cases that can be caught with a slow sweep test with a lab scope.
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Old 04-12-2018, 06:52 PM   #13
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My thought: Set the DSO to single sweep with a trigger of 4.55 volts. I have had good luck finding glitches with that. Also a fast min/max DMM can grab some very short events.
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Old 04-12-2018, 07:14 PM   #14
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My thought: Set the DSO to single sweep with a trigger of 4.55 volts. I have had good luck finding glitches with that. Also a fast min/max DMM can grab some very short events.
A DSO is a great tool dont leave home without it LOL

For instance things the intermittent blowing of a fuse. Monitor the problem circuit with a DSO and do a wiggle test, in many cases you will see the voltage change on the DSO well before it pulls enough current to blow the fuse. When that wire in the circuit brushes across a path to ground but only a picosecond but yet not long enough to blow the circuit fuse, as you know it will stand out on a DSO like a sore thumb and now you can go hunting it down and now know what path to take to find it.

Happy Trails
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