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SallyRWerner · 11-07-2014, 04:07 PM

We have a 2006 Tiffin Allegro Bay Class A motor home with a 300 hp Cummins engine. The "check engine" light comes on under a hard pull. We took it to a diesel repair shop and they replaced the Delta P sensor. It seemed to help, but then we went on a 2200 mile trip to Montana. The light still comes on....but on a harder pull, going up a steeper grade. Any suggestions would be appreciated!

Melmoses · 11-07-2014, 04:42 PM

Did they clean the radiator? Check the coolant level? When was the air dryer replaced last? Any of these can cause a check engine light on a hard pull.

Dutch Star Don · 11-08-2014, 12:24 PM

When was the last time you replaced the fuel filters. They will trigger an engine light if they are starting to get plugged, especially under a hard pull. They're relatively cheap to replace and is where I would start before taking it to a shop again.

Coma · 11-09-2014, 06:06 AM

Also fuel related is that some of those engine have a weak lift pump. If the filters don't help have it checked.

YC1 · 11-09-2014, 06:55 AM

Don beat me to it again. Fuel filters can easily cause an issue. Even on flat ground if one plugs it can make the light come on. I always carry spares and have changed them twice at rest stops.

jth camper · 11-09-2014, 11:16 PM

I had a similar problem with my 2010 cummins. After replacing, fuel filters, air filter, and adding Diesel Kleen additive replacing both fuel filters again the problems was still there. I finally took my coach in to a repair facility. A New, or should I say rebuilt turbo and $5400.00 later my check engine light problem was solved. Thank goodness for Xtra ride, they covered all but $260. of that bill.

cristelectri · 11-10-2014, 11:41 AM

My problem is that my amber check engine light comes on when I'm going downhill not uphill. It only happens when I use the exhaust brake?

Air Baron · 11-10-2014, 01:05 PM

Why guess with your wallet? Call around and take it to a shop where they have the correct code reading software for your particular engine S/N. I pulled into Las Cruces and found a Peterbilt dealer with a mobile mechanic who had the software on his laptop. When he returned to the shop, he plugged in to my engine and read where the code for fuel restriction had registered 7 times. The shop then changed both filters and off I went across the desert.

mrv8outboard · 11-11-2014, 07:09 AM

I have an 08 ISB and have had intermittent VGT/exhaust brake issues. These start as carbon and exhaust debris builds up on the moving components of the VGT (which is also the exhaust brake) and causes sticking or limited travel. This will set codes. The light may go on and off and not leave it in history (it should). If you have codes that lead to this being your issue a turbo replacement would be recommended. Some have had success with removing and cleaning the turbo. I used a product called "Revive" just before my Florida trip (leaving from Cape Cod,MA) and my issue is gone. I did modify on how to apply the product and it has worked well for me.

Dutch Star Don · 11-11-2014, 03:17 PM

"Air Baron"....I'll disagree a little. I think your statement is correct, but if the OP returns and states that he hasn't replaced the filters in years, and is capable of doing so, he should. First, the filters need to be changed regardless. Second, check engine lights on hard pulls are often caused by plugged/low flow filters.

If he returns and tells us the filters are new, then he should do as you advise, but if they aren't why pay a repair shop $120.00 plus dollars just to diagnose and another $120.00 to install the filters. He may more than likely solve the issue for the price of the filters!

Air Baron · 11-11-2014, 03:47 PM

"Dutch Star Don" your point is well taken. How does the saying go..."If you think education is expensive, try ignorance?" Since my introduction to fuel starvation 101, I have since changed my fuel filters several more times and carry both spares. I will change them again before heading out next spring. I avoid bio-diesel like the plague and I have purchased algaecides on numerous occasions, prior to any extended stay...which I always add to the tank before filling.

However, if the OP has a lift pump or fuel injecton pump problem, he will not solve it by changing filters.