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Good morning all

  I have a 2001 Monaco Executive with the 500 hp Cummins my warning light came on so I checked fluids and all were good. Since I had just bought the coach I took it in to have oil changed and everything checked out, so everything is good except they can not get the light to go out. The codes they are showing  Sid 151 through 155 are all manufacturers code for r and d or along that line  also code 231 bottom line they can’t find anything wrong but can’t turn the lights off only have 40000 miles on the coach. Any help would be appreciated 


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First, what warning light are you getting?  

Here is a link to Cummins lamp ID guide:

https://www.cummins.com/sites/default/files/files/brochures/Cummins Driver Lamp Identification Card 4971518.pdf

Next, you will not get a light that means the oil needs changing.  Most check engine lights are related to sensors on the engine.  

When were the fuel filters changed?  Many of the issues with these large diesel engines are related to the fuel filters.  

Where did you take the coach for service?  Do they have a certified Cummins technician with the proper diagnostic equipment?

Do you have a complete list of the codes?

Edited by vito.a
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I drove mine for a year with the yellow warning light on before anyone could figure it out, a shop in W.V. ran a code test. That showed barometric pressure module.

As Cummins had an updated wiring harness for the sensor,  they installed both.

They erased the code, I have more power and the light never came on again.


Right technician 

Correct code reader monitor.


I have the 500 ISM


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I have read that the old style coolant level sensor could cause a problem of not reading correctly.  Solution was to remove sensor, use a scotchbrite pad to clean the crud off of it and reinstall.    Not sure if this applies to your engine coolant system or not. 

The old style sensor was mounted into the top of the surge tank down into the coolant.  I believe it is a 1 wire sensor that senses that the coolant is at the correct level and is grounded through the chassis.  I think if you unplug the sensor and take it ground & the light goes out that would solve your problem. 

Maybe someone else can chime in.

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Legit mine came on last year. Then stop engine. Everything  Ran fine and fluids were  Perfect. Have to take mine into Cummins turned out to be an oil pressure sensor there are 2 on Monacos. One for the motor ecm and an extra for Monaco's dash cluster. My dash oil sensor was bad that why it still ran fine but had a stop engine light.  Seems like everything was doubled on our coaches kind of unnecessary but that's the way these were made.

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  • 4 weeks later...

Finally got the coach out of the shop after the shop had to shut down for 2 weeks because of COVID. They could not get the warning light to go off, he did clean the coolant level sensor, no change.  They said what ever caused the light to go on is not coming from the engine computer.  So I guess I drive it for a while and see if it goes off

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