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Old 05-20-2023, 12:34 AM   #1
Junior Member
Winnebago Owners Club
Join Date: Mar 2014
Posts: 12
Cummins ISB CM2150 Wait-to-Start light doesn't go out or extinguish

I have a 2010 Winnebago Journey with a Cummins ISB CM1250 engine on a Freightliner chassis. During the pandemic I took the RV out for a 750 mile camping trip in October of 2021 with no issues. After returning home, I broke my ankle severely and the motorhome sat, like me, without being exercised until now. I talked to my go-to RV repair person on the phone and he indicated that, because the fuel tank was full, he doubted that I had problems with the diesel fuel going bad.

I went over yesterday to check to make sure that the fuel tank was full, only to discover that my generator was running! It has been running for quite some time, because the fuel was down to half... (I'm the second owner, and in looking through my Winnebago user manual tonight I read that the generator can be set to start on it's own under certain circumstances, but I haven't checked on that yet.) Since the generator had been running, I decided to turn on the RV engine. Unfortunately, I didn't follow the wait-to-start protocol, but simply turned on the engine, let it run for about 30 seconds (I know, I know...) and shut it off.

Meanwhile, I have an appointment on Tuesday to replace the fluids and filters needed, so, since the generator had been running, I decided to start the engine again, and this time to let it run before bringing the RV to my home for the service.

Finally, getting to my issue (!) I inserted the ignition key partially and the "wait-to-start" light came on as usual. I waited for it to go out. And I waited. And I waited. After about 20 minutes, I gave up because the light never extinguished. I did not want to make matters any worse by again starting the engine before the light went out, so I just left.

Any thoughts about how I should proceed from here? The RV service that will be replacing the fluids and filters is a mobile service, and I could call them to come to the RV storage area rather than to my house, however the service company is exclusively for filters and fluids, not general service.

Of course, I can and will call Cummins next week before proceeding if I don't get any replies or helpful suggestions.

Thank you very much. Rhonda
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Old 05-20-2023, 07:57 AM   #2
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Join Date: Mar 2019
Location: Braidwood Il.
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There is an intake manifold temp sensor tied to lamp. If it doesn't show/return proper temp the light will stay on. It can still start easily over 70f. Another thread in search had pack rats had chewed the insulation off the wiring.
The house batteries being low can trigger generator auto start. The plug to genny remote being wet and dirty has also caused random starts as well as animals standing/climbing on the start switch. One owner found kitty prints on his genny and starting it more than once.
95 Monaco Crown Royale
M11 400hp, 4060 trans.
Aquahot, Generac Guardian7.5k
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Old 05-21-2023, 03:41 PM   #3
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You won't hurt anything by trying to start without an OK from the Wait light. It will start or it won't - generally it will start easily as long as the ambient temperature is moderately warm, say 60+.

The light indicates the heater in the engine air intake has warmed up the incoming air. Either the heater didn't come on (fuse? burned out heater element) or the temperature sensor isn't reading the intake manifold temp. A chassis service tech can troubleshoot it, but you can drive to a shop if needed.

As 153stars described, it's not all that rare for Onans to start up on their own due to moisture in the wiring harness or animal damage. There is also an Auto Generator Start option available, but you would probably have noticed the control panel for that if you had it.
Gary Brinck
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL
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Old 05-23-2023, 05:00 PM   #4
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Thanks Gary and 153Stars

Thanks to you both for your replies! I did bring the motorhome to my house today to have a local on-site oil company drain and replace fluids and filters that were on the Cummins checklist. He was very helpful.

But more to the point--the "wait to start" light went out almost immediately after I went ahead and started the engine (with the "wait" light still lit. Hopefully it was just a passing occurrence... (do those every happen in an RV?! In my limited experience--not usually...)

I'm excited to finally be getting ready to hit the road again--even for a short trip to make sure everything is humming along.

Thanks again!

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