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W202 5 spd auto box won't stay in 5th

GadgetBoy

Active Member
Joined
Aug 19, 2011
Messages
145
Location
Belfast, N. Ireland
Car
ML320 and CLK200K Cabrio
I've (a) never had a Merc before and (b) never had an auto before so my expectations may be unreasonable but ........

If my car stays in 5th for more than a nanosecond I would be shocked. Even going down hill if I put a gram more pressure on the throttle it shifts down to 4th and then will only change to 5th if I come off the throttle. A gnat's wing flap will cause it to downshift.

Is this normal?
Is there something mechanical I can do to cure it?
Is there a software upgrade?

It's doing my head in and my fuel consumption is attrocious.
 
It may well be normal for a sport, my Classic will change down from 5th to 4th at anything under about 50mph. Not sure but think that changing from S to W might make some difference but then you will always pull away in 2nd which could be a bit of a surprise when you need to go. What fuel consumption are you getting?? Sorry don't know about software upgrades.
 
Low 20's and I'm not a boy racer.

What sort of driving? If mostly around town then a low 20's figure is not unusual.

The 240 is a 2.4 (or 2.6 depending on model year) litre engine but not particularly powerful or endowed with that much torque for the size of engine so add that to a heavy car and an automatic gearbox and you will not get spectacular fuel consumption figures.

My W203 320 petrol averages 27mpg on a mixed run of country roads and fast A roads. On a long motorway run I get closer to 34mpg true.

There are a number of things to check that can cause higher consumption figures, one being the lambda sensor. Do you have the last MOT with the emissions data? If so it should state the lamda sensor value.

Does the car warm up as expected? If not a faulty thermostat will also give poor fuel consumption figures especially on short journeys in cold weather.

There may also be a problem with the Mass air flow meter. This can cause problems such as poor response and lower power requiring larger throttle applications and may make the gear box kick down to a lower gear more often. Perhaps your best line of approach here is to find a local MB specialist who has the STAR computer and get them to check it out.
 
If I got 30 on a long motorway run at 70 mph I'd be ecstatic.

Just been MoT'd and no emissions issues.

Hmm. Thermostat. I think it's slow to warm up but it's my first Merc so I have nothing to compare it to.

I have CarSoft and no issues/errors logged.
 
I've (a) never had a Merc before and (b) never had an auto before so my expectations may be unreasonable but ........

If my car stays in 5th for more than a nanosecond I would be shocked. Even going down hill if I put a gram more pressure on the throttle it shifts down to 4th and then will only change to 5th if I come off the throttle. A gnat's wing flap will cause it to downshift.

Is this normal?
Is there something mechanical I can do to cure it?
Is there a software upgrade?

It's doing my head in and my fuel consumption is attrocious.

As you probably know yourself, this is not normal. When accelerating at higher speeds you should be able to move the throttle without it dropping a gear. It will sometimes drop a gear of course, but that's normally under harder acceleration. I've heard people on this forum say that you should change the gearbox oil regularly (every 40k miles or so) on these gearboxes and that it makes a huge difference to the gear change and performance. I'm no expert however, so it might be worth getting it checked out by a specialist.
 
If I got 30 on a long motorway run at 70 mph I'd be ecstatic.

Just been MoT'd and no emissions issues.

Hmm. Thermostat. I think it's slow to warm up but it's my first Merc so I have nothing to compare it to.

I have CarSoft and no issues/errors logged.

Carsoft and other OBD software is OK for reading some fault codes but you cannot interrogate gearbox ECU's and many other aspects of the car and the associated electronics with it. Find someone with STAR and let them run a full diagnostic on the car. It may well show fauts with the gearbox or other areas and you can then focus your energy and money on fixing the problems rather than us all guessing.
 
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.....................There may also be a problem with the Mass air flow meter. This can cause problems such as poor response and lower power requiring larger throttle applications and may make the gear box kick down to a lower gear more often.............


This was my first thought.^^^

Will it rev freely to the 'red line' in the lower gears?
Do you generally need to use a lot of throttle?
Is it generally fairly lazy on acceleration?
Does it change up through the gears without backing off the throttle?

I have seen airmass sensor faults reported as gearbox faults a zillion times - and a zillion is a lot.
 
If I may correct you.

Carsoft does a full module-by-module diagnosis. There are no errors logged for the engine or transmission.
 
If I may correct you.

Carsoft does a full module-by-module diagnosis. There are no errors logged for the engine or transmission.

Have a look at the self adaptation in the ME-SFI (I seem to remember you can do this on Carsoft), it may be close to limit values (which will not log a code).
 
Right. Hold on a minute here. We're drifting off in different directions what with Carsoft and thermostats and all that.

Let me better explain the gearbox problem.

If I'm travelling along a flat road at 45 mph and I press the throttle firmly (not to kickdown) to overtake someone it should downshift. I accept and understand that. However, if I want to gently accelerate up to 50 mph I would expect the car to stay in 5th.

The problem is the car changes down to 4th with little or no throttle change or gradient change. I've even had the situation where it constanly hops between 4th and 5th as if it can't decide what gear to be in.
 
Have a look at the self adaptation in the ME-SFI (I seem to remember you can do this on Carsoft), it may be close to limit values (which will not log a code).

Sorry Alex. You snuck that one in while I was typing the previous message.

I'll have a look at that. Thanks.
 
If I may correct you.

Carsoft does a full module-by-module diagnosis. There are no errors logged for the engine or transmission.

My error, thanks for the clarification. I know that generic OBD readers generally do not have the ability to access gearboxs etc.

I would still strongly suggest a good MB specialist with STAR though. I have not had time to look at the Carsoft website and info but can it access all that the STAR system can?

It would be quite useful to have it that were so.
 
The version I have will access everything on earlier cars. Pre-2003 I think. There are newer versions which will talk to the newer cars.
 

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