It’s not exactly Where’s Waldo, but Holiday Rambler customers are wondering why they can’t find the exhaust brake on the new Vacationer Diesel and Scepter models with Cummins engines.

“It’s there,” John Wolf assured me. If anyone would know, it’s Wolf, a service technician with Monaco Coach Corporation for 19 years. “What we’ve done is install the exhaust brake into the engine, so all you can physically see are two sensors on the outside.”

This new exhaust brake system is called Variable Geometry, or VG Turbo, for short. There are a variety of reasons why Cummins chose to incorporate the exhaust brake into the engine, most of them related to performance.

“With VG Turbo, we’ve designed a system that pinches off an orifice to increase or decrease air pressure — sort of like the garden hose analogy,” Wolf explained. “What you get from this ability to restrict the exhaust gas is improved acceleration, more efficient engine response and better braking.”

The only way to get a handle on understanding this new exhaust brake system was by trying it out. So, with John on board, we headed for the hills where the roadway reaches a seven percent grade.

“VG Turbo is [installed] in the new ISL 400 engine and some of the ISB engines,” Wolf said. “Unfortunately, there’s no way to upgrade, so you can’t add the system as an aftermarket item.”

Operating the VG Turbo is similar to past exhaust brake systems. Engage the exhaust brake switch when you’re out on the highway, but turn the switch off when you drive around town. Keep your foot 100 percent off the throttle on steep grades, and depress the service brake when it is necessary to go slower or bring the vehicle to a complete stop. How the system feels is a pretty good indicator of how well the brake is operating. “But you can also check the gauge to monitor boost pressure,” Wolf suggested.

Laptop computers have replaced toolboxes and broken knuckles in modern day technical troubleshooting. For this test drive, Wolf brought along his diagnostic software.

“It doesn’t go anywhere I don’t go,” he said.

A data port, which is usually located either up in the cockpit or back in the rear engine compartment allows a service technician to plug in the cable and bring up real-time information on what the exhaust brake system is doing.

Incidentally, improvements also have been made to make the data port itself create faster and more accurate communication between the engine and computer. “The old style data port was like a walkie-talkie,” Wolf explained. “You could talk to one component at a time. This new type, the J19-39, is like a telephone line. Different parts can communicate at the same time.”

Standard repair protocol with this new technology involves driving the motorhome, so the computer can diagnose the problem, return to the shop for repair, and then undertake one more brief test drive with the computer plugged in to confirm the problem is fixed. This process enables the technician to fix all system failures the first time.

“The computer takes the guesswork out of what part of the system is compromised,” Wolf said.

Software programs are available for coach owners who are interested in monitoring the VG Turbo. However, don’t get your hopes up that this will provide the cyber answer to that age-old question of how much fuel produces how much turbo. “Before, we were getting 22,000 variables,” Wolf said. “With the new system, there are 22 million.”

The base software available for the VG Turbo system will check fault codes and read diagnostics, but prohibits program changes. For more information on obtaining the software and the suggested cable requirements, contact your Cummins dealer.

There is a significant reason the VG Turbo is finding its niche in the RV market. “The former exhaust brake system came with a number of care and maintenance requirements, but the VG Turbo is maintenance-free,” Wolf said. “You don’t even have to worry about it in storage.”

Nor do you have to be concerned in high humidity when traveling long distances. There’s always the chance of a compromise at the switch or a loose wire, but technology has improved these areas enough to reduce risk considerably.

The exhaust brake hasn’t disappeared, it’s just been reinvented. And with better performance guarantees, plus zero maintenance, I think you’ll agree that this is one mystery we don’t need to solve.