If you are still having the problem, I maybe able to help.
Dave in post #2 stated that yours should be powered by a Cat engine. If it is a Cat, if you can get the engine serial number from the valve cover engine data tag. The serial number will start with a prefix with 3 letters and or a combination of two letters and a number, example 1AJ or 5GL or CKM. If you can get the serial number prefix, I can get you some info regarding your problem. I have access to the Caterpillar Service Information System.
Do you know if there is a diagnostic switch on the dash, or maybe under the dash. Most truck manufactures have a switch installed, not sure if the chassis manufacture for the motorhome you have has one installed. If there is one, you can flash out the diagnostic code. If so give that to me and I can get you the troubleshooting info.
If the motorhome has a Cummins engine, I will need the engine serial number also. There should also be a tag on the valve cover or on the left front of the gear case cover. The serial number is all numbers 7 or 8 digits. I can get service info for Cummins engines also. If Cummins powered, there may also be switch to flash out the codes.
When I know what engine you have I can get you the info on the procedure to read the codes.