Saturday, December 2, 2023


Ask Dave: Why does the check engine light come on intermittently?

Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the RV Handbook and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses an intermittent check engine light.

Dear Dave,
I have a 2005 Fleetwood Providence 39L motorhome with a 350 HP Cat C7 diesel engine. After starting it and pulling out, in a short while the check engine light comes on. It will stay on for about 5 minutes then it goes out. There are no other warning lights on and the engine runs smoothly. The light does not come back on until after I stop for a day or two, then the same thing occurs. Is this a warning that something is about to go bad or something simple? Thanks! —Ardo

Dear Ardo,
There are numerous issues that will make the check engine light come on. Some are big issues such as exhaust items with oxygen sensors or emissions to fuel pressure. It can also be something as simple as your fuel cap is not on or is not venting properly.

Since your rig is 2005, it is not a diesel exhaust fluid (DEF) or NOx (nitrogen oxide) sensor issue, as they were not required until 2010. That is a great thing for you as these can be “gremlins”. If the trouble you are having is an emissions or fuel issue that can be major. The check engine light will come on and stay on and typically you have only so many starts or miles driven before it goes into “limp mode”.

Since it’s going off after 5 minutes, it seems to be an intermittent problem that is correcting itself somehow. Your engine’s computer will store the error code that signals the check engine light. Cat diagnostic codes are termed CID codes and are used to diagnose component failures and require a proprietary code reader. Most error codes in automobiles can be read with an On-Board Diagnostics system (OBD) at any service facility, parts store or auto dealership with a code reader compatible with the car.

The computer will store the codes until they are reset by a service technician or the battery is disconnected for a certain amount of time. So your authorized Cat dealer should be able to hook up and find the component that is triggering the check engine light.

I would suggest gathering as much information as you can to give to the technician. What time of day, how many miles, ambient temperature outside, engine temperature from your gauge, fuel level, running the generator while driving, anything you can identify to help isolate variables and find a common denominator for the technician to work with. Hopefully it’s just a sensor that has a diode that is opening with temperature changes.

Read more from Dave here

Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.


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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.



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Ken (@guest_138822)
2 years ago

Real quick. No offense.

Not “Knox” but NOx sensors.

Diesels do not have evaporative emission requirements and therefore will not set a CEL for fuel cap issues.

Good advice otherwise!


RV Staff
2 years ago
Reply to  Ken

Thank you very much, Ken! This proofreader is not a mechanic (that’s what I have two mechanically inclined sons for 😉 ) – so I had no idea that was incorrect. It’s been fixed. Have a good night! 🙂 –Diane

Bob p (@guest_138738)
2 years ago

Good answer! Cat engines were always powerhouses but fuel economy and emissions finally ended their rein in on road production. I drove truck for several years and the owner was always a Detroit Diesel fan, his son in law was an International dealer and talked him into buying several trucks with the Cat engine. That was the last time his SIL sold him a truck as the Cats got 9% less mpg which is a lot when you’re running 115k to 125K miles per year. He switched to Freightliner and never looked back.

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