Transmission slipping

Here’s my suggestion: Start from the top! First, take your Mercedes to a good, independent service shop with trained technicians. I honestly would suggest going to a dealer who has NIASE-certified techs and who have access to the latest Mercedes-specific diagnostic software.

Second, I would have them run a complete diagnostic on the unit. I know you have had diagnostics run as you seek specific answers, however, I don’t know if you have taken a systems analysis approach. In other words, look at the whole powertrain as a complete system and then begin your hunt from there. In this way, you can take steps that might otherwise be missed. For example, let’s say you the manual or test manual calls for a test of the engine’s Engine Control Module (ECM) or the master computer for the whole vehicle. This is the system that can listen for up to a dozen reports from subsidiary systems that impact the operation of your vehicle.

As you know, there is a specific transmission control module (TCM) which is responsible for the operation and reporting of the transmission and its subsystems. The interesting thing about this is that if you were to look at a schematic diagram of the reporting systems in relation to the transmission you will likely find that the brakes may be (and do) report to the TCM. Likewise, the emissions system — or parts of it — report to the TCM. The Mass Air Flow sensor and Mass Air Pressure sensor, as well as various wheel-related sensors all report to the TCM in order for it to choose the right gear when certain conditions are met. The Throttle Positioning Sensor and Coolant Temperature Sensor also report to the TCM (the transmission has its own piece of the cooling system in most vehicles).

As you can see the TCM reaches out and touches a number of related systems that actually either report directly to the ECM or to the ECM and other subsystems which is why I think you need the systems analysis approach to the problem.

Quite frankly, I think that if you were to replace the ECM or the ECM and its related boards, I think you would see most, if not all, of the problems that your transmission is experiencing clear up. I say this because, as I see it, there is something compromising the signal flow to the ECM. It could be the ECM itself or one of its related parts.

Since it is likely that this automotive powerhouse is throwing problem, it is more than likely having not only an impact not only on the transmission but also the engine componentry as well. It doesn’t hurt to replace the ECM and it is a relatively inexpensive fix for your transmission problems. If the problems continue, swapping out the TCM is your next move.

Remember, though, all of this should be done after your technician has run down all of the leads that may have been generated by the system-wide diagnostic.

Get your Merc out of there yesterday! I am not kidding! There is no reason on this green planet that they should ask you for your driver’s license and registration. About the only reason I might suspect is this: they are going to try and open you a line of credit so they can do the work and get paid for it. You, of course, would be left with the bill. Now, I don’t know if this is the case, it is just my sense of caution jumping up and down, but, when asked for something out of the ordinary, I am not easy with it.

As the the price, the general cost of a new transmission in your part of the country — I do know of the area — should be about $4,400, but, that’s for a more standard car like a Toyota Camry or a Honda Civic. Mercedes-Benz vehicles are notoriously expensive to service so the $6,200 isn’t all that outrageous, however, I think it is too high, myself. A car is a car is a car and a transmission is a transmission is a transmission — and here’s the but — a Mercedes is expensive to repair. However, in 05 they had more standard transmissions without some of today’s improvements like dual-clutch or dual-clutch and eight-speed, so your 350 should come in, I would think, about $5,200. I know it’s not much comfort, but, if you have to replace a transmission that’s what it is.

Again, here’s my advice:

1. Get the Merc out of there
2. Find another independent shop who specializes in Mercedes-Benz cars
3. Have a thorough diagnostic performed with the most up to date software
4. Get a print out of all of the issues identified
5. Sit down and talk with the technician and discuss the diagnostic report

I think you may find, as I suggested, that the problem is in the electronics. It could also be in the mechanical stuff, but, I don’t think so.

Let me know what you think of the plan. You will have to factor in the cost of the trip to the new shop on a ramp truck or on a tow hook (I prefer the ramp myself). One last thing, they might try to tell you that you can’t take your car out; that you owe them the work, and such stuff. If they haven’t done anything except give you a date for completion it seems to mean that they haven’t done any work?

You never did tell me if they had done work, did they? If so, then you could be on the hook for everything because of various things including a goodie called a mechanic’s lien where the mechanic can keep your Merc in payment of the bill, if you don’t pay it. Please let me know if they did any work and what promises were made by both sides. I’d be happy to help you work this out — via email as I am not on the West Coast and it’s the best way.