How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask sprinkles08 Your Own Question
sprinkles08, ASE Certified Technician
Category: UK Car
Satisfied Customers: 22692
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
Type Your UK Car Question Here...
sprinkles08 is online now
A new question is answered every 9 seconds

Have 2002 CLK 320. That won't rev over 4250 rpm in park,

Customer Question

Have 2002 CLK 320. That won't rev over 4250 rpm in park, Neutral and Gears and won't engage in D or R gears. Have changed the Conductor plate to no effect and seem to be running out of options! Any ideas kind regards, Chris.
JA: How old is the transmission? Have you checked the brake switch?
Customer: Assume it's the original system, forgot about brake switch but how does that effect the rpm?
JA: What is the make/model of your car?
Customer: Mercedes CLK 320 (Avantegarde)
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: Yes, replaced the conductor plate as I've had a couple of P0715's before the car totally failed to engage gear.
JA: Anything else you want the mechanic to know before I connect you?
Customer: No, I believe what I've supplied covers the fault and my attempted repair!
Submitted: 1 month ago.
Category: UK Car
Expert:  sprinkles08 replied 1 month ago.

Hello and welcome to JustAnswer!

If the vehicle doesn't move with the shifter in gear and the linkage is moving correctly at the trans then you either have a mechanical failure in the trans or possibly the differential.

With the trans in park are you able to push the vehicle or do you feel a mechanical lock?

Customer: replied 1 month ago.
The Park lock is correctly engaged. Can only push vehicle a very narrow range a few inches back and forth. Would it be possible for you to email me a complete fault finding procedure for the symptoms I've described (won't rev past 4250 and won't drive/move in D or R) rather than a step/response approach as the delay in such an approach is almost unworkable. Please note I have a icarsoft OBDII reader but do not have access to a star diagnostic system. Kind regards, Chris.
Customer: replied 1 month ago.
Or you can call me on +44 (0)7895422043 (my UK Mobile number), which your call me web procedure won't allow me to enter!
Expert:  sprinkles08 replied 1 month ago.

I'm not able to talk on the phone.

Your problem is mechanical or hydraulic failure in the transmission, repairing the problem is either going to require replacement of the transmission or removal, disassembly and overhaul.

Not revving past 4,250 RPM in park and neutral is normal operation. The rev limiter is lower in park and neutral to prevent engine damage from needlessly revving the engine.

Customer: replied 1 month ago.
would a Star Diagnostic narrow down the transmission problem, ie the valve control unit, K3 clutch ect, or would it be a case of suck it and see as there are no obvious signs of ware or damage to the transmission unit components and the valve solenoids all activate with 12V applied (Conductor plate has been replaced). Is it possible for the Gearbox control module to be defective without producing any DTCs, if so can it account for the symptoms exhibited by the vehicle? I have the Mercedes service manual that covers this vehicle, and assumed it was a conductor plate problem. So, I could use a little help (proceedure) to eliminate/find the cause of the transmission failure! Thanks in advance, Chris.
Expert:  sprinkles08 replied 1 month ago.

A scan tool doesn't diagnose a problem, that's up to the technician.

Diagnosing the internal transmission failure is going to require removal and disassembly.

It isn't possible for an electrical problem to prevent the transmission from engaging. As I mentioned you have an internal failure in the transmission and it needs to come out for disassembly or replacement.

Customer: replied 1 month ago.
Which was my original conclusion, that has been undertaken, and as I've already stated, there are no signs of damage or wear in the planetary gear set or the valve control unit. Hence the replacement of the conductor plate, assumed that the gears wouldn't engage because the Hall effect sensors were un-serviceable after a couple of P0715 notifications! Hence my question regarding the ETC control module (N15/3). Just so there is no confusion I'm an electronics and computer systems Design Engineer by profession with a lengthy and in-depth experience of Autonomous agents, with 35 years experience of Mechanics including cars, boats and planes, I'm therefore experienced and able to repair systems at the component level but in order to do so I need specific knowledge pertaining to the system under test. Therefore, in order to eliminate sub-systems from the main transmission system and then isolate the defective component(s), I need a gearbox specific testing procedure, otherwise, from the symptoms initially provided, you could easily say the car needs to be stripped down checked and re-assembled. Being an experienced Mechanic you'll know that replacing an entire gearbox is expensive and locating a gearbox problem without a system specific procedure is problematic to say the least! If you know of a way to check the (static out of unit) serviceability of the Hall Effect Sensors on the Conductor Plate, that would be a great help in eliminating the Conductor plate from the equation, since even brand new parts can be defective as I've learned to my cost on a number of occasions! Look forward to your reply, kind regards Chris.
Expert:  sprinkles08 replied 1 month ago.

You don't need a testing procedure, you need to disassemble and inspect the transmission or replace the transmission.

An electrical problem cannot prevent transmission engagement.

Customer: replied 1 month ago.
Has been done, with no faults found!!!
So, not helpful!!!
Expert:  sprinkles08 replied 1 month ago.

It was not previously mentioned that the transmission had been removed, disassembled, inspected and rebuilt. However, that does not change the fact that the problem is internal. I would recommend seeking the help of a transmission shop or dealer.

Customer: replied 1 month ago.
Again not helpful, but how could the planetary gears and the valve control unit have been checked for damage and wear, without removing and disassembling? Are you just providing guidance using a to system level check list?
Expert:  sprinkles08 replied 1 month ago.

If you were unable to find the problem on your own then I would recommend seeking help in person of someone experienced in transmission repair.

Customer: replied 1 month ago.
I'll take that reply to mean that the problem is outside of your knowledge base, are there any other 'Experts' with who would be able to progress this problem?
Expert:  sprinkles08 replied 1 month ago.

There aren't any that could provide the in person help that you need. I've had dozens of these transmissions apart and am one of the top experts on the site, but it isn't physically possible for someone to know what is wrong with your transmission remotely without seeing it.

Customer: replied 1 month ago.
I can relate to that, however, given the symptoms. What have been the most common component(s) failures in the transmission which have produced said symptoms. Your, personal findings in the past or your best guess now would be helpful, as I'm no longer a spring chicken and hauling a transmission unit about is getting a lot more difficult for me, so I'm not asking for a definitive but more a sense of 'The Usual Suspects'! I should then be able to take it from there, drawing on my own General experience with such things!
Kind regards,
PS. Any list of usual suspects would constitute very helpful information.
Expert:  sprinkles08 replied 1 month ago.

Complete lack of engagement is usually caused by geartrain failure, clutch failure or lack of line pressure but there isn't a 'usual suspect', which would allude to this being a widespread issue with a single cause on all or most vehicles. Each problem, each time on each vehicle can be different and has to be diagnosed as such. The problem could be the pump, input shaft, geartrain, hydraulic leakage in the case, a shaft or piston, there may be damage to shaft splines or geartrain that was overlooked.

Customer: replied 1 month ago.
Am I correct in assuming that all electronic problems can be disregarded as the physical gear selector would ensure that the gearbox would always engage, even if only in limp mode, unless there is a problem with the mechanical aspects of the gearbox? And am I correct in assuming that a faulty valve control unit can also produce these symptoms? As you can appreciate I took great care in checking out the splines, Geartrain and the Clutch and Brake Components,since they are the most difficult to remove and replace!
Expert:  sprinkles08 replied 1 month ago.
You can completely disconnect the transmission connector and it will still engage forward and reverse. Lack of engagement entirely can only be a problem internal in the trans.
Customer: replied 1 month ago.
Thank you, ***** ***** I think I'll change the valve control unit first as that is easy enough to do and take it from there! Have a good weekend, well what's left of it.
Kind regards,
Expert:  sprinkles08 replied 1 month ago.
You're welcome and good luck with it!