I own a 1999 Beaver Monterrey, 30' powered by a Cat 300 paired to an Allison MD3060 6spd transmission. I want to help others who run into an issue where the shift selector shows an error condition, or nothing at all. This tends to happen after swapping out chassis batteries and is almost always due to either reconnecting three wires in the battery box incorrectly or a bad ground.
Always take a photo of the wiring before disconnecting anything (ask me how I know). In particular look at the 10 gauge wires connected to positive and ground and make certain that you reconnect them properly. In the harness in my coach they are the same color, so no indicator of which is positive and ground.
Next look at the condition of the connectors, clean them up, possibly replace them if the wire is breaking down at the connector or other corrosion exists. If you havce a flakey connection, it WILL lead to problems!
That all being good, also check for the VIM and ECU power fuses which are also likely in the battery box. If these also check out, then find the location for the ECU and VIM. In my coach they are located in behind an outside door, driver side, front along with terminal blocks for a lot of the coach wiring. There are two fuses in the VIM, check those out as well and make sure they have power.
OK now that you have all this confirmed or fixed, and no change at the shift selector, you might wonder if the ecu is bad, and what your options are. I strongly recommend that your next step is to go to the Transmission Instruments webpage I am linking here and carefully follow the troubleshooting steps on the page:
https://www.transmissioninstruments.com/troubleshooting/
I found this site and thought that even after using the guide that my ecu might be bad. Being stuck outside Ft. Worth, Texas on a road trip, I was willing to do just about anything to get my coach running again. I called the company, reaching the owner:
John Kopalek
Owner
Transmission Instruments
972-353-8286
www.transmissioninstruments.com
It turns out that he was physically located about 45 minutes from where I had my RV towed. We agreed that I could bring my ecu to him to test out. John has created the test equipment to quickly determine if the ecu is good or bad, as well as the shift selector. Within minutes, John convinced me that the ecu was good, then spent about 45 minutes teaching me about the interfaces (three harnesses connect to the ecu) and how to test the pinouts on them to find the problem. This info is laid out in the link above, read it!
John also had a WTech III shift selector in inventory, so I bought it from him to assure I had a good one at hand. Armed with the knowledge of how to test the system, and one good part under my arm, I headed back to the shop that had my coach. The shop owner was very gratefull to work with me on the problem, given there is no schematic online that (nor was there one in my manuals) helped us isolate the problem of no display on the shift selector (and therefore, no start from the ignition switch at the driver seat.
Knowing that the ecu was good, we focused on the pinouts of the harness that supplies power to the ecu. This power comes from the chassis batteries, is not switched, so take care with your testing. We found that there was power where we expected grounds on two of the pins, which sent us back to the battery box. It turned out that one of the 10 gauge wires had "shortened" by falling back, through a hole in between the battery box aqnd the engine compartment, making it appear that it only fit on the positive terminal of the back battery. After tracing it into the engine compartment, and finding extra length there, we pulled it back into the box, and reconnected to the negative terminal, along with the other 10 gauge ground hooked up there. Now we had ground on the pins as expected. I had that wrong! (always take photographs of the wiring before disconnecting chassis batteries).
But, we still had no display on the shift selector. With everything checking out to the ecu and the VIM, it was time to look at the ecu outputs. They looked good as well, so we decided to assure we had a good ground between the ecu output and the selector. We hacked the harness at the ecu out connector and moved the ground wire with an extension to ground at the terminal block adjacent. Turned the key on, and everything lit up, the engine started and shifting was enabled.
The key here, and this not just from my personal experience, but from John at Transmission Instruments, is that you MUST have a solid ground and that this is #1 problem most of the time. Whether from rodents, from a corroded connection, or because you are a bit of a knucklehead like me and do not photograph the battery connections before swapping batteries, a bad ground in the ecu circuit will cause failure.
After we fixed the two issues I had of an incorrect connection AND a bad ground somewhere in the harness, I took the now-unneeded spare shift selector I had purchased from John and put it in the mail back to him, expecting a core charge refund. John is a saint. Not only does he test the ecus for free, he refunded my entire cost of the shift selector! He wound up charging me nothing for his expertise. I strongly recommend that you use John if you ever have suspected ecu issues.
