At 172,000 miles, the 2015 Ram 2500 tow truck has handled everything I have thrown at it with zero drama. Equipped with the 6.7 Cummins inline-six and 6-speed manual transmission, this truck is built to run to 500k and beyond. But there is one known ‘weak link’ in this fantastic motor. The Variable Geometry Turbo (VGT) from Holset, and specifically, its electric actuator. A system that would start acting up on my drive back from PRI. And become markedly worse over the next few weeks.
I will walk through my case to serve as a guide for others facing similar issues. Through this process, I found many conflicting opinions when VGT carbon buildup is the cause of actuator failure. With the general recommendation to replace the full turbo in this scenario. Costing anywhere from a 3k-8k. However, after inspecting my turbo, I concluded that replacing the actuator and cleaning the VGT system would bring my truck back to working order. I have included some background and a few (notes:) to help along the way.
How the Holset Variable Geometry Turbocharger (VGT) Works
First, a little bit on how the Holset VGT works on the Cummins motor. This system uses a sliding nozzle ring to adjust exhaust gas flow. The variable gas flow allows the turbo to behave as both a small unit for fast spooling and a large unit for high power. It also eliminates the need for a mechanical wastegate. Instead, an electronic actuator moves the ring in response to engine conditions to adjust boost. Additionally, the system can increase backpressure, serving as an exhaust brake.
Symptoms of Actuator Failure
When the VGT and/or the actuator act up on these engines, it is very obvious. You will have one or more of the following: poor throttle response, lack of power, erratic boost engagement, possible overboost or no boost, excessive smoking, and no or intermittent exhaust brake.
The symptoms my truck exhibited are as follows. A month ago, my engine lost all boost on two separate occasions shortly after driving from cold. The loss of boost lasted around 15 seconds on both occasions. I was jump-starting the truck because its batteries were weak at the time, and I didn’t think much of it. No CELs were thrown, and I figured something wasn’t happy with the cold starts.
Then I drove the truck to the Performance Racing Industry trade show in Indianapolis without incident. Although on the way back, the P003A CEL was registered. Afterward, when using the truck the following week, I would consistently register P00AF and U010E. The no boost condition would intermittently return and last longer. Furthermore, the exhaust brake joined the party and would disappear for minutes at a time. Since I live in the mountains, I knew the truck would strand me soon, so I took it down for maintenance.
Diagnostics
One of two turbo failure modes is indicated by the CELs and will almost always result in a failed actuator. In short, all three codes have vague descriptors indicating an issue with the turbo actuator’s ability to move the VGT.
- P003A – boost control ‘A’ position exceeded learning limit
- P00AF – boost control ‘A’ module performance
- U010E – lost communication with reductant control module.
In short, the actuator is having trouble moving the VGT. In my case, it gets stuck in the open position, resulting in no boost and virtually no acceleration. And as the no boost duration increased, the truck would start to ‘roll coal’ like that was its job.
(Note: If your truck is smoking like mine was above, stop driving. The engine is still adding fuel as if it were under boost, so it is running super rich. This will eventually cause piston damage, as the cylinders are being flooded with far too much fuel relative to the air being ingested.)
Diagnosing the Turbo Actuator
Step one after this failure is diagnosing the turbo actuator and the VGT lever. This is done with the turbo on the engine. First, you will need to drain the coolant. The actuator connects to the turbo’s coolant loop, and if you remove it before draining the coolant, coolant can enter the actuator’s electronics. You can either disconnect the lower radiator hose or open the plastic radiator drain (hex key) on the driver’s side of the radiator, well below the power steering reservoir.
Now remove the actuator. Two methods are available here. It can be accessed from the top of the motor. This is what I did, but you will be working blind on some of the hex bolts that hold the actuator to the turbo. Alternatively, remove the passenger-side front wheel well to access it more easily.
Once the actuator is removed (4 hex bolts), test the gear for motion. To do this, with the actuator plugged in, have a helper turn the ignition to the ‘run’ position. The actuator will perform a sweep test. Anything other than a smooth sweep is bad. There should be no stalling, jittering, etc…
Below is a side-by-side comparison of my old actuator and new actuator.
As you can see, the old one is having a seizure, and the new one has a clean sweep on the key on/off.
Turbo Inspection and VGT Failure: the Chicken or the Egg
Obviously, my actuator had failed, but what caused it? At 172,000 miles, these failures are common, but I wanted to ensure the turbo was functioning properly before replacing the actuator. First, this turbo has zero shaft play and spins like new. We could never say that about the old turbos we used to run in the early 2000’s. Before canning a good turbo, I inspected the VGT lever.
Given the initial intermittent nature of the failure, I suspected my VGT was binding due to carbon buildup. You can test this by moving the gear lever on the side of the turbo. This is what the actuator gear moves. It should move smoothly and relatively easily with one finger. If you have to apply more than a little pressure to move it clockwise or counterclockwise, you likely have excessive carbon buildup in the VGT, which is causing resistance. It is normal to hear a metallic click at each end of the sweep.
Unfortunately, I did not record a before video, but mine felt like it was dragging and binding during initial testing. A perfect candidate for cleaning.
However, I have an after-cleaning video below that demonstrates how the system should move when it’s not bound.
As I said, mine felt heavy, so before spending 3k on a new turbo, I wanted to see if I could fix the VGT by cleaning it. To do this, I would need to remove the turbo.
(Note: Make sure to check the VGT motion before installing a new actuator. Bad VGT motion will kill a new actuator quickly, and these things aren’t cheap.)
Removing the Turbo Notes
I am not doing a full write-up on removing the turbo from the Ram 2500. There are many guides online, and I will link a few below. However, I do have notes.
I want to offer a fair warning. This process was way harder than the edited videos online make it seem. Part of that was due to a well-placed ‘FU’ nut the engineers installed on the system. ‘FU’ nuts are exactly what they sound like. Where engineers place something in such an inconvenient location that anyone with even normal-sized hands will curse the day the engineer was born.
Second, this is an inline-six in a 3/4-ton truck, and you will need to perform some unusual maneuvers to remove the turbo. Often including doing the Superman on top of the engine.
(Note: The combination of a 2-hour job (removal) turning into an 8-hour exercise in frustration due to a single ‘FU’ nut on the back of the turbo exhaust housing led me to the conclusion that removing the turbo and the manifold together is the way to go. Once I switched to that approach, removal was quick, and reinstall took only an hour after cleaning.)
Turbo Removal Video and Checklist
I found this one covers almost everything.
Here is a quick list for reference.
- disconnect battery negatives
- drain coolant
- remove intake to turbo (remove the box as well for extra room)
- Disconnect the boost outlet tube
- remove top oil line to the turbo
- remove top coolant line to the turbo
- disconnect actuator wire
- disconnect temp probe wiring
- disconnect turbo sensor wiring (starts at top of turbo)
- disconnect downpipe
- disconnect turbo oil drain (bottom)
- disconnect turbo coolant line (bottom)
- remove 4 nuts from the mount flange at the manifold
At this point, the turbo should come right out. YMMV, and I highly recommend pulling the turbo with the manifold if you get stuck on the nut below. Makes things so much easier.
Battling the ‘FU’ Nut
A little more drama, and then I will proceed to the cleaning. The nut that has given me so many headaches is the back nut closest to the engine, which mounts the turbo to the manifold. There is only enough room to slide a 15mm standard-length wrench on, and no feasible way to get any leverage.
In the end, after trying multiple angles and busting several knuckles, I got out the big guns. I tried the torch, the air hammer, and finally, cutting. The reality is, I had to use a borescope just to see where I was working, and in the end, after many wasted hours, I gave up. Opting to pull the manifold with the turbo attached. I then removed the nut on the bench. Ironically, I still had to use the torch and the air hammer to budge it.
Cleaning the Turbo VGT
To clean the VGT, remove the exhaust housing from the turbo to expose the exhaust wheel and VGT ring. The VGT vanes sit on a cylinder that moves up and down around the exhaust wheel. My ring was not moving smoothly; it initially felt stuck and then required some force to move from stop to stop.
To clean any carbon buildup, I sprayed the VGT and exhaust wheel liberally with engine/brake cleaner. Any cleaner that works on carbon. Then I would let it sit for a few minutes before turning the assembly upside down. Small black carbon fragments and leftover cleaner would then drop out. Next, I raised the VGT cylinder to the highest position and repeated the process. Ensuring I sprayed the now exposed cylinder wall liberally as well. Again, a few more minutes, then inversion and more debris.
Finally, I sprayed everything again while raising and lowering the ring. After a third inversion and additional debris, I used an air compressor to flush the system. I repeated the cleaning process until no further small carbon fragments were detected. For me, this was two full rounds of cleaning and one full can of cleaner.
Ultimately, the VGT motion improved significantly, requiring only one finger and minimal effort to move the system through its full range.
Reinstalling the Turbo Notes
Of course, reinstall is the opposite of removal, with a few notes. First, since I removed the exhaust manifold, I went ahead and replaced the manifold gaskets and the turbo gasket. Also, reinstalling the turbo’s oil drain is a monumental PITA. It was ‘FU’ nut round 2.
The oil drain is a ‘flexible’ hardline that will likely bend out of alignment during removal. And realigning it on your back while threading 2 x 10mm bolts with a new gasket onto the turbo cartridge is a nightmare. I found a couple of companies that sell 3-piece flexible drains, which I will switch to if I ever have to do this job again.
And finally, and this is important. Do not reinstall a new actuator at this point. I learned the hard way that calibrating the new actuator is a 2-part process, with step 1 requiring a sweep cycle with the actuator disconnected from the turbo.
Calibrating and Installing the New Actuator
Actuators aren’t cheap. So I opted for a remanufactured unit from Circuit Board Medics. This company was priced in the middle, and they rent the calibration tool. The tool rental was important because you have to calibrate the actuator to the turbo. This would save me $500+ on an expensive scan tool that may or may not work, and/or the logistics of getting my truck to a shop.
Alternatively, I found a self-calibrating actuator from City Diesel, but the 14-day ship time was a non-starter for me.
(Note: It is worth repeating because one of the hex bolts on the actuator mount is a PITA to install, but Do Not install the actuator until the calibration tool instructs you to. I found the included instructions a little vague around step six, and got to remove and install the actuator an additional time because of this.)
With that said, the process is simple. Rotate the VGT gear on the turbo to the clockwise stop. Plug the calibrator into the wiring harness between the new actuator plug and the harness. Turn the ignition to ‘Run’. Then follow the on-screen prompts. Once the new turbo actuator is calibrated and installed, make sure to refill the coolant before starting the engine.
Results
I am happy to report that the results were immediate. Replacing the failed turbo actuator and cleaning the VGT brought my truck back to life. I now have full boost, no smoking, and no idle issues. It is back in service just in time for the race season to resume.
As a quick reference, if you encounter these issues on your Cummins-powered Ram 2500 with the Holset VGT turbocharger, here is a summary to troubleshoot:
- Check the actuator by draining the coolant, removing it, and testing the gear sweep.
- If the actuator is bad, test the VGT gear level for smooth motion.
- If motion is smooth, replace the actuator.
- If motion is heavy or appears stuck, and there is no shaft play in the cartridge, and it spins smoothly, remove and clean VGT.
- If the turbo fails any of these tests after cleaning, replace the turbo and actuator together.
Future Changes
As I mentioned at the start, this truck has been insanely reliable since new. However, performing this extensive work in the Ram 2500 engine bay has left me wanting to tweak a few systems. I plan to simplify the engine in several ways to improve future reliability and serviceability. Small changes, such as the grid heater delete and the electric radiator fan conversion, are on the horizon. I also plan to replace the VGT system entirely when the turbo ultimately requires replacement. But hopefully that is at least a year off, when I can afford to pull the truck out of service for an extended period. As always, I will share the process and results as I make these changes. Til then.
