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RV Tech Savvy: Check-engine Light Woes

Originally Published in MotorHome Magazine


We own a 2006 40-foot Holiday Rambler Ambassador diesel pusher with the Roadmaster chassis. There are currently about 55,000 miles on the odometer. For the last 8,000-10,000 miles, we’ve had the problem of the “check engine” light coming on and going off while driving. We’ve noticed that tapping the throttle will make the light go out. There’s no pattern. We never know when this might happen. We’ve taken the motorhome to two RV shops and two Cummins dealers. The RV shops had no answer and one of the Cummins dealers suggested taking it to a Holiday Rambler repair facility. After researching, we determined our motorhome needed to go to the Factory Service Center in Coburg, Oregon. Last summer, the technician found a solenoid or something in the throttle that senses the need for more fuel. That part isn’t available any longer so the technician suggested living with the problem and taping over the check engine light on the dash! After thinking about this we feel like we can’t be the only owners out there with this problem. Have you heard of this problem and do you have a solution to it?

Everett and Judy Ross | Arkansas City, Kansas

Whenever there is a trouble code set, write down the number of the code for reference. This is very important. When the battery pack is disconnected the code(s) will be lost. I don’t recommend the “tape over the warning light” suggestion. There should be an accelerator-pedal position sensor and an actuator at the engine that receives signals. The unit may be worn, dirty or corroded. Generally, Cummins dealers are best at handling Cummins engine-related problems such as this. I suggest taking the motorhome to a different Cummins dealer and explaining the situation. There may be some kind of misunderstanding; parts for this powertrain should still be available. If necessary, I would try calling RV salvage yards once you have a specific part number.

Sprinter Vibrations


I own a 2015 four-cylinder, Mercedes-Benz Sprinter 3500-based motorhome from Great West Vans. It has about 40,000 miles on it and has been serviced according to factory recommendations. The motorhome has performed very well; however, from the beginning there has been a persistent vibration in the steering at higher speeds. After going through trial and error (on original Continental Vanco Four Season tires) of balancing, alignment, rebalancing, realignment, tires-out-of-round suspicions, tire replacements, supposed wheel (steel) distortions — all at a local tire shop — the problem persisted. The Sprinter specialist dealer diagnostics led to another “alignment” and eventually to a “tightening” of the two-piece steering column. That last step was after a long trip that resulted in two bald front tires from thousands of miles of high-speed shimmying. The tightening reduced the shaking/shimmying by about 90% in the 55-70 mph range.

The Sprinter dealer service rep said that for a couple of years the Sprinters had a two-piece steering shaft, but the company has gone to a one-piece shaft, as it is more “stable.” My motorhome’s model year, 2015, was one of those years. With new tires in front, balanced and aligned (the four back ones are fine), I embarked this past spring on an 8,000-mile trip. The improved (reduced) vibrations were tolerable; however, I stopped in Alabama at a Sprinter dealer and the mechanic found the steering shaft attachment to the frame (yoke) at the bottom was not torqued adequately. He tightened the “play” and I drove it for three days; the improvement was drastic.

Have you heard of any other Sprinter RV years, 2015 or thereabouts, with this type of vibration problem? Or, with tales of two-piece steering shafts and Sprinter then going to single steering shafts because of “issues” with the two-piece ones? Can a two-piece steering shaft be replaced with a one-piece shaft? Any leads or suggestions would be welcome as even the very minor residual vibrations in the steering (at highway cruising speeds) would be desirable to eliminate. At this point, after the Alabama road trip work, the vibrations are truly minor, but are still there at highway cruising speeds. Perhaps that is inherent in these rigs.

Ben Stolpa | via email

There are a number of things that could be causing the vibrations. Generally, the one- and two-piece steering shafts don’t generate vibration and would be expensive to change. There is a coupling between the two parts; if that is found to be tight (lacking slop or slack) it should be fine. If the motorhome has simulators rather than aluminum wheels, remove them and road test. I would recommend having the wheels balanced at an authorized Mercedes-Benz Sprinter dealer that uses the Haweka Pro 6 wheel-balancing adapter set and the Hunter Engineering GSP97MB Road Force wheel-balance machine. The Haweka Pro 6 adapter is set to get the Sprinter-based RV wheels perfectly true with the balancing machine’s rotational axis. The Hunter GSP97MB is the MB Sprinter USA recommended Road Force balancing machine for MB Sprinter dealers. Also have the rear wheels balanced with the Haweka Pro 6.

A number of 170-inch-wheelbase Sprinters have vibration problems with the long three-piece driveline. There are some driveshaft specialty shops that can straighten/rebalance the existing driveshafts using specialized balancing setups.

Rather than endlessly change parts, I suggest finding a shop that has a Fluke Vibration Analysis device to determine the frequency of the vibration and address the actual source of the problem. Here are some examples from Fluke Connect.

If you touch the Fluke Vibration Meter probe to the steering wheel when driving 65 mph in fourth gear (direct 1:1 ratio through the transmission), the meter can identify a wheel balance or out-of-roundness issue or whether there’s an engine vibration, or more likely a driveshaft or driveshaft steady bearing issue. The Fluke meter will quickly locate the frequency, which will lead directly to the rotating element that’s vibrating.

Maintenance Schedule by Mileage and Time


We have a Coachmen Mirada 35KB on a Ford F-53 chassis. I have searched online/inside the Ford chassis owner’s manual and have generated a list of chassis maintenance items. Unfortunately, this information details mileage/time intervals for some maintenance items but for other maintenance items there is only a mileage interval listed. My motorhome remains stationary for long periods, and I want to make sure I perform proper maintenance on items where only a mileage interval is listed. Is there a definitive maintenance list for a Ford 2014 F-53 chassis that details all recommended chassis maintenance with both mileage/time intervals noted for each item?

More RV Tech Savvy Discussion

Greg Loy | via email

Ford does provide time intervals where appropriate, such as for oil and filter changes: “Every 5,000 miles or six months.” Ford publications are the “definitive” listings and if a time interval is not indicated along with mileage, it can be inferred that more frequent service is not needed. Of course, in extreme cases where vehicles sit for years, fluids and lubricants should be changed before returning the vehicle to service. Owner’s manuals are available for free downloads online.

Axle Ratios


Why are axle ratios on motor­homes typically from 4.10 to 5.38:1? For over 45 years I have run and ordered tractor trailers, which run throughout the U.S. pulling 53-foot trailers and up to 80,000 pounds, and doing a fantastic job with 3.73:1 rears. The rear-axle ratios used in motorhomes reduce the fuel economy, for certain. I had a dealer tell me that they must have those ratios because they pull cars and trailers. Is there a better explanation for the crazy ratios?

John J. Dunn | DeLand, Florida

The motorhome gear ratios you mention are typically used with gasoline engines. A lower gear ratio helps get a heavy vehicle moving and up to speed, and is needed to get over grades at highway speeds. Considering that motorhomes are rarely driven at speeds faster than 75 mph, lower gear ratios do not dramatically affect fuel economy. The 3.73:1 ratio you mention for heavy trucks is used with large turbodiesel engines. Diesels have very high torque and run at roughly half the rpm of gasoline engines at the same speed due to their different torque curves and overall designs. Tire diameter and gear ratios also greatly affect overall gearing. Tractor-trailers like the ones you mention also have a lot more gears in the transmission, which allow more flexibility in the final drive ratio.

Subaru Towing Question


I have been towing my 2015 Subaru Forester (manual transmission) behind my Triple E Embassy Class A for about 15,000 miles. After returning from a recent trip, I was driving the unloaded car when both rear coil springs simultaneously broke, leaving me with no rear suspension at all (out of warranty, of course). I’m wondering if there is something about the way I am towing that caused this unexpected failure. One thought is that part of the problem might be how the car is loaded while towing. I usually fill the rear cargo area with bulky items like golf clubs and a dining tent, and a few items in the rear seat area, but no items in the front seats. I am using a Roadmaster Sterling tow bar and Roadmaster brackets on the car, installed as per Roadmaster’s instructions, and all are still solid. Is coil spring fracture a common occurrence? I would appreciate your thoughts as to a possible cause.

Paul Fryer | Belleville, Ontario, Canada

Rear spring breakage is a fairly common problem on these models, and it often occurs at fairly low mileage. I don’t think the load you carry is at fault. I have even heard about instances in which a spring broke while an empty car was being serviced at a Subaru dealer. In some cases, Subaru covered all or part of the repairs under a goodwill policy adjustment on vehicles out of warranty. I suggest you contact Subaru and see if the company will do anything for you.


Ken FreundMotorhome 101RV DIYRV TechRV Tech SavvyTech topics

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