[Doug]

Found the relays. Pulling the relays have no effect on the dash indicator light and nothing in the Allison troubleshooting manual for this issue. I must be the lucky one, since no one has replied…any ideas as to why the dash light will not turn off?

[Jim]

Jim, I may be way off base but check your brake lights. The dash light could be connected with the brake light when activated. The retarder light can be disconnected from the brake light. I met you at Mr Olivers RV years ago when you were shopping for a Prevost. Darrell

[Archived]

Jim, have you pulled up the Prevost electrical diagrams for your coach. Prevost installs the retarder switch and it sounds like switch or relay contacts are welded shut.

[Raymond]

Hello Darrell, yes, I remember you and thanks for the reply. I’ll be sure to check that out. It seems, looking at the wiring diagram, the brake relay and engine fan relays could provide a ground feedback to illuminate the retarder tell tel operation light.

Hello Jon, I agree that it would or should be a welded relay and I am pouring through the wiring diagrams now…the relay now in question is what Allison calls K5 in the VIM transmission control box/forward steering box. All of the Prevost installed relays for retarder control, brake control and engine fan control seem to be operating correctly. I plan to dig into it this weekend and I’ll post an update.

Thanks to you both!

Jim

[Archived]

Hello all. As I promised, I will bring everyone that would be interested up to date on the logic of the transmission retarder tell tell light.

Knowns were: engine cooling fan in complete lock up high speed, illuminated trans retarder tell tell light and zero trouble codes set. I was really hoping for a code so this job would be easy and in fact, I looked for the easy button first before asking for help on this great forum, LOL. I had hoped of a response of “Oh yeah, that happened to my bus and this is what I did…”

Retarder operations appeared to be normal, however, flipping the retarder on/off dash switch to “off” would not cut the light. Pressure switches on the brake system test normal. Thank you Darrell. At Jon’s suggestion, I poured over the wiring diagrams, and yes, scratching my head multiple times in the process.

Nowhere in the troubleshooting manual does it mention any function of the light as a trouble signal, but it does mention if the retarder stays on it could be 3 things: 1. Autoflow valve spring weak, 2. Autoflow valve stuck “on” and 3. “K” solenoid stuck “on” (welded).

Testing the relays, 30 is line power in, 87 is line out, 85 and 86 is the control side of the coil. On a good relay, with an ohm meter, 30 to 87 should be open, if not, the relay is welded closed. 85 to 86 should read around 80 ohms for proper function of the coil. If it is open, no coil closing will take place.

All of the relays on the Prevost side test proper. On the transmission side all relays tested good, none were welded closed.

I phoned a local Allison transmission guru to ask if the light had any meaning related to trouble with the system. He relayed to me that to his knowledge, any issue known by the ECM would be presented as a code. Other than that, the light “on” condition would have to be a short to ground in a wire or the ECM was faulty. I’m so happy the ECM was not the issue.

Rechecking the K5 relay in the VIM, vehicle interface module, I found(missed this on the first round) a strange reading of 8 ohms not 80 Ohms on the coil, allowing wire 125,retarder indicator) to feedback ground for the light “on” condition. And in addition, the ECM was fooled to apply constant fan.

Replaced the relay and everything thankfully is back to normal operation.

[David]

Excellent post Jim, glad it was something simple.

[Archived]

Does not look like a SIMPLE fix to me. I would have never been able to make this repair. Good job Jim.