Written by the Motorplex Team
Offering RV and motorhome repairs in Auburn and Spokane, Washington.
When an RV enters the shop, especially a well-used diesel coach, the work rarely involves a single isolated repair. These vehicles are complex, integrated systems in which engine performance, electrical circuits, air systems, cooling components, and more all depend on one another.
We had a customer bring their 2006 Monaco Diplomat into the Motorplex RV repair shop in Auburn. The owner was concerned about active voltage codes on the dashboard after a recent alternator replacement. The coach was shutting off, and he needed a diagnosis. In addition, he requested a preventative maintenance and transmission service.
To do the job right, our technicians knew they had to evaluate the entire system, identify risk points, and restore safe, reliable operation before the unit returned to the road. This case provides a clear example of that process in action.
RV Repair Troubleshooting and Repair Begins
The coach arrived with multiple known concerns and underwent our structured, multipoint inspection and repair process. All completed work was performed to restore core mechanical reliability and address safety-critical systems first.
As suspected, the alternator wasn’t charging the system properly. In addition, we found that the radiator needed replacement and that the entire coolant system needed to be flushed and refilled. We got the parts on order and started the repairs.
Preventative Maintenance for the Win
This RV owner knew the importance of regular engine and mechanical maintenance for his beloved coach. We gave it a full preventative maintenance service, including engine oil, filters, fuel filtration, water separator service and chassis lubrication.
Additionally, the RV received a full transmission service and rear differential service, and we replaced the axle flange gasket and stud to ensure it was sealed and ready to roll. These systems are foundational to safe operation. Addressing them early ensures the drivetrain is protected before road testing begins.
Additional Systems Checked and Serviced
A large motorcoach like this one has many moving parts and complex systems. We continued our inspection to include the air, electrical and exterior systems. Here is what we found and how we remedied it:
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Air system leak diagnostics completed- Faulty air valve identified and replaced
- Entry step system diagnosed and repaired with a new controller installed and tested
- Mirror lighting and front turn signal circuits corrected
- Left blinker circuit diagnosed for intermittent fault conditions
- Multiple electrical issues were found and fixed
Air and electrical systems on older coaches often degrade gradually. Since this RV had been on the road for 20 years, it was important that we did an overview of these systems. Finding minor issues early is key to performance and safety.
Additional Findings Identified During Inspection
During full-system diagnostics and repair, additional issues were identified. This is a normal and expected part of comprehensive RV servicing, particularly on older diesel coaches where systems have undergone years of modification, repair, and wear. The customer asked us to do a deep dive into potential issues, as he wanted it to be perfect for the upcoming season.
These findings were clearly documented for customer approval before any additional work proceeded.
Water pump system diagnosis: The pump wasn’t responding when we flicked the switch. We had to do a deeper diagnosis to figure out what was wrong with it and fix it.
Coolant reservoir leak: The reservoir was leaking and needed replacement.
Rear air tank crack: A structural crack was identified in the rear air tank, and the tank needed to be replaced.
Turn signal wiring was makeshift: Multiple “DIY-looking” modifications were found throughout the circuit, causing cross-signalling faults. The cleanest fix at that point was to run all new wire to the affected circuits.
We sent the client another transparent estimate, which he approved, and we completed all the work.
New Radiator Installed
Motorplex’s Commitment to Safety, Transparency, and Reliability
Every stage of this project reflects Motorplex’s core operating standards:
1. Safety-first diagnostics Critical systems such as air brakes, cooling, and drivetrain components are prioritized immediately.
2. Transparent communication
All findings are documented and communicated before additional work is performed.
3. System-level thinking
Repairs are not performed one at a time or on their own. We evaluate how each system interacts with the next and ensure the entire RV operates at its best.
4. Verification before release
We always test every repaired system to ensure it works perfectly. In addition, our technicians take the vehicle on a road test to ensure everything is right as rain before returning it to the customer.
At Motorplex, our focus remains on long-term reliability, not short-term fixes. If the customer doesn’t want to move forward with repairs, we are open and honest about what could happen to the vehicle. At the end of the day, we help ensure every RV leaves the shop with confidence built into every mile ahead.