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Getting the demons out, one at a time……
Well, just when I thought there was nothing more that could go wrong with my new to me coach while on the road, I found another demon.
Travelling to Florida (and reasonably close to Columbia, SC) my wife and I pulled over to have lunch at a rest stop. When I started to get back on the road, I discovered I could not put the coach in gear! The Allison gear selector display showed an “I”, which I have come to find out means “Inhibit”. In other words, “Shift Inhibit”. This is essentially a limp mode that allows you to get safely home or at least off the road, but does not allow you change your range (drive, reverse, neutral, etc.). This actually happened a few days ago while in Mountain Falls, NC, but I ignored it. Big mistake!
Turns out, it threw a 2511 code which is related to the transmission output shaft speed sensor. Fortunately, we were only a few miles from Columbia, SC and found WW Williams (Detroit/Allison shop). They were fantastic BTW! Keep in mind it’s 2:15pm on Friday and they quit at 4:00pm! The tech, who has worked there for 15 years, went to work and quickly diagnosed the problem as a wiring issue. He said in his 15 years of doing this, he has only replaced a sensor one other time and was fairly certain it was a wiring issue. I was skeptical.
Sure enough, there is a TCU (transmission control unit) wiring loom that runs from the TCU to the shaft speed sensor. This wiring loom runs right across the oil fill tube and had worn through the wire insulation, causing a short to ground. You could see evidence on the oil tube….green corrosion and some rust where the wire was running. The tech mentioned that this is common for my vintage coach. He demonstrated the problem to me by putting an ohm meter on the wire (to ground) while moving the wire. This caused the meter to fluctuate showing there was a pathway to ground.
He ran a new wire by extracting the pin out of the TCU connector and replacing the wire. Much better repair than splicing in a new section of wire IMO. I opted to have him replace the speed sensor proactively, even though he had clearly found the issue. He finished up around 3:45pm and we were back on the road by 4pm! AWESOME!
Just wanted to share in case someone else runs into this issue. Also wanted to give a plug to WW Williams in Columbia. Great people and great service on my first visit to them.
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17 Replies
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Marshall thank you for the info. I travel that way often between Carlisle and Sarasota.
Bill III
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Marshall – THANK YOU for sharing that experience!
So glad you had an experienced tech as he surely saved you significant time and dollars.
Good heads-up for us all to thoroughly inspect all wiring harnesses.
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Probably as a result of plane ownership prior to trips and at every 5000 mile service interval I am under the coach looking for all the little things like that. I admit to being anal, but I also recognize little simple things like chafing wires or hoses or belts or air lines if left to wear through can stop a trip in its tracks.
The age of a coach likely has nothing to do with whether something is at risk of chafing because we have so may wires, hoses, or air lines running near wear points or running through holes with no means of securing them from rubbing or preventing moving parts from wearing through them.
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yes…..I woke up last night in the middle of the night with the realization that I simply could have “insulated” the wire from the oil fill tube and driven to a more convenient place for the repair. Fortunately, my issue was intermittent enough I was able to restart the motor and drive a few miles to the shop.
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Jon you anal…who knew:)
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That was great service Marshall, hard to come by these days.
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Experiencing the EXACT described issue this morning, July 10, 2022 while 2,000 miles from home.
Marshall, or anyone… I have a 14L Series 60 and the mentioned harness is not affixed to the engine oil fill tube.
Might it be affixed to the transmission oil fill tube? (Seems this would be more likely yet too far back for the tech to have shown Marshall the corrosion)
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If I remember right there are 3 sensors on the trans that can cause erratic conditions. My issue was an 06 chassis too.
Mine was the wiring clip going into a sensor on top of the trans. I was in PHX and also Williams sent a tech out who knew the location and reached up unplugged it and rewired the clip and all was well.
There’s a number of places this can happen or it could be a sensor.
Are you anywhere close to have someone put a reader on it?
Later
bv
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Thank you for your reply, Bernie!
I just got off the telephone with Marshall who guided me to the “known” wiring harness location where his tech informed him last October where the wiring commonly rubs through the wire loom / wire insulation.
I carry jack stands and will check it out asap. IF this is the cause, and not simply the failure of the OUTPUT Speed Sensor (code 25-11) I will repair it here in my campground, then also pick up a new sensor prior to leaving our current campground.
***Marshall state the location is upon the engine oil dipstick fill tube on the 14L Series 60. I will followup and include a photo if at all possible. MY “symptoms” were identical to Marshall’s symptoms.
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Yes moving the wires could remedy the problem to move if you need to.
If you change out the sensor I believe you need the software to adjust it. Check that with Allison.
Later
bv
Jeff and Lindsay
91 Marathon XL -
I experienced the issue on the way to ETLC where we were putting on a seminar. I could limp in 1st gear and since it happened 1/2 mile from home I initially decided to go home which required an 8 mile drive “around the block”. But by another mile the condition cleared and the transmission shifted normally.
It turned out to be the transmission speed sensor which Jeff diagnosed and changed. It was a fast fix and now 3 years later never repeated itself. The wiring was good.
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Great info, Bernie & Jon. THANK YOU
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
Good Morning – Installed a new Output Speed sensor a few days ago in our campground due to the exact same symptoms & code Marshall experienced and drove it for the first time yesterday.
Now no more code or red check transmission light.
The Frogg Toggs rain suit sure made crawling around in the gravel easy LOL
One Note: The new sensor has a straight connector whereas the original had a 90 degree connector. Was able to get written confirmation in the form of an Allison publication that the straight connector was indeed the correct, updated part #
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Jeff. Great follow-up to my original post. Glad to hear everything came out positive. This forum is invaluable for anyone who owns a PREVOST bus. Thanks for the follow-up.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
Thank you Marshall,
Forgot to mention, I did check my wiring harness as you suggested by telephone and found no issues.
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