Allison tranny service light - Throttle Position Sensor Low

[Busded]

I'm having trouble with my 93 HR Navigator. The service light on my transmission shift panel lit up on my way home last week. I called the service center we've had work on it, and they said we were fine driving home so I did. When I looked it up in diagnostic mode, the code it set is for the "Throttle Position Sensor - LOW" according to the code sheet I have.

Problem- I don't have a clue where that is located to check for good ground, etc. and how to track down this problem

What I know- the tranny fluid is at the right level, pinkish, doesn't smell burnt, and the guage for temp is good per the installer. The Exhaust break switch, when engaged, changes the shifter readout from 6 to 2 when engaged, so the switch is good, and the tranny responds accordingly as it did prior to the SERVICE light. If I leave the exhaust break switch ON, the transmission won't leave 2nd gear, so I shut that switch off when traveling home. And, it shifts WAY better (I don't think i'm imagining this) when i put it in the "MODE" setting (economy)

Any ideas as to tracking this down before I head to the dealer with a handful of cash again?

[mtrumpet]

dougmac wrote:
Code 22-12?
The ECU is receiving a voltage signal that is below normal.
There are several possibilities:
1-The sensor is miss-adjusted into the error zone.
2-There is a shorted or open circuit on the signal wire (156 blue) or the TPS high wire (124 red)
3-failed TPS
4- a very remote but possible chance that the ECU is bad.

Five volts should be supplied to the sensor on the 124 red wire. As the TPS is cycled through its range the voltage on the 156 blue wire should vary. It should no go below 0.5 volts.

I had a similar problem a couple of years ago. It turned out that one of the cables plugged into the Transmission ECM had worked it's way loose on one side, just enough to cause the error code every once in awhile. Unplugged it and plugged it back in, making sure that the connector was well secured and haven't had a problem since. Not saying that this is your problem for sure, but might be another thing to check.

[Busded]

I did some deep exploration, and have determined that the little brass fixture like the one pictured in the thread is, in fact, worn thru on my setup. I know you mentioned making your own, does anyone know of a source for this part or is it a simple thing I can pick up at a cummins dealer part shop?

Also, I want to confirm what the local service center told me about driving with this light on- they said its fine to drive this way- is that true?? I have work in Wisconsin on wednesday & thursday, about 7 hours drive each way, am I ok driving that? it shifted fine coming home the few hours I drove, but don't wanna wreck something.


Thanks so much, you guys are a wealth of info and a great help!

[dougmac]

Code 22-12?
The ECU is receiving a voltage signal that is below normal.
There are several possibilities:
1-The sensor is miss-adjusted into the error zone.
2-There is a shorted or open circuit on the signal wire (156 blue) or the TPS high wire (124 red)
3-failed TPS
4- a very remote but possible chance that the ECU is bad.

Five volts should be supplied to the sensor on the 124 red wire. As the TPS is cycled through its range the voltage on the 156 blue wire should vary. It should no go below 0.5 volts.

[SCOMP225]

John,
Took a look at that bracket you referenced and Mine doesn't have that style.
I do use these->>
I had one machined from S/Steel and we made a bronze sleeve that slides into the bracket. I check it for wear every one in a while but all is good after 50 K Miles.

[jtfcons]

Go to the RV Chassis Parts web site and see for the 8.3C mechanical engine that there is a "Bracket, TPS" available for around $145. The pin that the sensor cable attaches to, via a slotted cable end, is part of this bracket. The pin on mine was nearly wore thru and gave erroneous info to the system ie low counts. The bracket is easy to replace from the passenger side access door to the engine, assuming your's is like mine. Also when assembling be sure to put a healthy dab of grease on the connection as there is no other provision to lube this junction and is the ultimate reason they fail. Other connections in the area have grease fitting type connections, but not this one, so lube it ocassionly.:( Yeah, the parts not that cheap, but I went this way rather than risk a makeshift solution to the problem.

[SCOMP225]

Yaj- Hit the nail on the head- not real happy with the way this is set-up myself. Mine broke a few years ago as the brass pc wore out- I carry a couple on board now and it seems right around 50K mile intervals it needs changed again. I just added it to my service list.

[Yaj]

I had the same problem last fall. It turned out to be the mechanical link where the sensor cable attaches to the fuel pump linkage. The same place where the throttle cable attaches. Passenger side of engine, there was a pin sticking out of the linkage assembly. The throttle position sensor cable is slipped over this pin and secured with a washer and a cotter pin. On our unit the cotter pin hole had worn through and the cotter pin fell out, allowing the sensor cable to slip off (the sensor cable has a oblong hole/slot where the pin fits through allowing it some freedom when the throttle moves to fast for it to keep up). I ended up removing the pin and using a 1/4" bolt with a regular nut to tighten it on the throttle linkage and a second nylock nut to hold the sensor cable on the pin while still letting it slide on the bolt.
It may sound complicated but if you can get a good view of the fuel injection pump linkage you'll see what I mean. I had to remove the back wall of a rear basement compartment to get to it. The linkage has three cables attached to it, the throttle cable, the cruise control cable and the throttle position sensor cable. If not that pin it could be the sensor cable itself.