2004 Mercedes CLK55 AMG Convertible... accidental purchase

[jhubs139]

So I returned to the UK for 6 months or so from Australia recently with the intention of buying a car to use while I am here for road and track duties. I sold my Megane RS265 Cup (regrettably) before I left with the aim of buying something similar here, however after a few beers and some browsing on a certain new auction site I thought sticking some speculative bids on a few interesting (and not quite track suitable) cars was a smart idea. The two that caught my eye were a 996 Carrera and a CLK55 AMG convertible with both needing a little love so I stuck a bid on each that I didn't think would come close to winning and left it there. To my surprise, the following evening, I was still winning both with an hour to go eventually only being outbid on the Porsche by a few quid and winning the Mercedes.

I went to collect the car a few days later expecting to find something that would struggle to get me the few hundred miles back to Norfolk given the ad had outlined a few issues. Luckily the journey home was uneventful (even managing 25mpg!).

So now to start bringing the car back up to scratch before a road trip to the south of France in June (but probably not track days).

The good bits;

- The car was owned by the same family from new and came with a huge folder of files and history (including the original sales invoice) up until about 3 years ago and its last service at 89k. The car has now done 100k
- The engine feels smooth and strong and so does the gearbox (mostly)
- The interior is in good nick cosmetically
- Tyres and brakes have been recently replaced
- The hood works and is water tight!
- Overall the car drives better than I expected

The bad bits;

- The engine management light is on (apparently it has been on and off since new) but doesn't seem to affect the way it drives. I want to cure this though
- The SRS and SRS service lights are on (again on and off since new)
- Slightly whiny power steering pump (hopefully just needs a top up of fluid)
- The gearbox is a bit clunky when cold going from 1st to 2nd so probably needs a service. Is very smooth once up to temp
- The electric seats have a mind of their own as to when they want to work and when they don't. Assuming some modules will need replacing
- The bodywork needs a general tidy up and a good cut and polish
- The wheels all need refurbishment

The plan is to take it to the local Mercedes indy for a long overdue service and diagnostics on the EML etc. Hopefully I don't leave there with the car condemned and I can start getting it up to scratch mechanically before dealing with the cosmetic bits and annoying electrical gremlins.

Future plans will include trying to liberate a little more noise (without being offensive) with some mods to the standard exhaust system and maybe trying to extract a touch more power from the V8 lump.

[Northbrook]

It looks nice. Enjoy!

[Tommie38]

Looks like a great buy. Lovely V8, I bet it sounds great with the hood down and they are still very quick thanks to the torque from the 5.4 motor.

On your todo list;
- Gearbox and differential oil change are well worth doing. I’d leave to a specialist because they can be a bit messy and it isn’t easy to get the levels perfect for the box.
- Seats are controlled by an air pump in the boot. Issue is probably that. Breaks in the hoses also possible but obviously they wouldn’t be intermittent.
- Removal of secondary cats is straightforward and won’t affect MOTs. Make sure the welds are not visible when refitted if you can.

Lovely cars and I would say one of the last classic Mercedes V8s. C63 very different (I’d guess a more fun motor but not as bullet proof).

[Gmlgml]

Without wanting to rain on your parade I hope the SRS light is an easy fix. I only remedied mine by buying a brand new ECU from Mercedes (cost about 450) as multiple attempts to code a 2nd hand ECU to it simply wouldn’t work, even after paying an ECU company to take 1 back to its virgin state and recode it with the right chassis number.

The Indy I used had all the correct Merc software and it simply wouldn’t take it. Also be aware they are buried in the car so labour to get at it and refit it mounts up.

The potential cause may be of interest to you as well as a word of warning, if you’re not going to use it regularly. It appears the solar battery panel I left plugged in wasn’t regulated and spiked it; garage said quite a common fault with this and things like flat battery-jump start. So don’t let it go flat!
Also be aware that the gearbox issues may be the conductor plate itself which isn’t cheap at around 500-600 for a refurbed one fitted (or does yours not have the 7G gearbox? In which case ignore me.)

[mwstewart]

That looks nice. I think that you have the basis of a good car. The SRS light could be any number of things, but the more common issues involve to the seat occupancy sensors, and belt buckles.

I will read the codes if you are close to, or pass through Lincolnshire.

[tobinen]

On my old 209 the SRS light was caused by chafing of the wire to the NSF seat base. A common issue IIRC

[jhubs139]

Gmlgml said:

Without wanting to rain on your parade I hope the SRS light is an easy fix. I only remedied mine by buying a brand new ECU from Mercedes (cost about 450) as multiple attempts to code a 2nd hand ECU to it simply wouldn’t work, even after paying an ECU company to take 1 back to its virgin state and recode it with the right chassis number.

The Indy I used had all the correct Merc software and it simply wouldn’t take it. Also be aware they are buried in the car so labour to get at it and refit it mounts up.

The potential cause may be of interest to you as well as a word of warning, if you’re not going to use it regularly. It appears the solar battery panel I left plugged in wasn’t regulated and spiked it; garage said quite a common fault with this and things like flat battery-jump start. So don’t let it go flat!
Also be aware that the gearbox issues may be the conductor plate itself which isn’t cheap at around 500-600 for a refurbed one fitted (or does yours not have the 7G gearbox? In which case ignore me.)

I am hoping the SRS isn't the ECU for sure. The previous owner seemed to have the issue diagnosed as related to the passenger seat but never followed through with getting it rectified.

Mine is the 5 speed gearbox (722.6) and from what I've read and been told they are pretty tough units. I will get the transmission oil changed as a starter and go from there

[jhubs139]

mwstewart said:

That looks nice. I think that you have the basis of a good car. The SRS light could be any number of things, but the more common issues involve to the seat occupancy sensors, and belt buckles.

I will read the codes if you are close to, or pass through Lincolnshire.

Thank you for the offer, the codes are being read by the indy on Wednesday so I will report back. The occupancy sensor for the passenger seat does throw up a seatbelt light occasionally when I'm driving alone so could be related. Like I said above, it looks like the last owner had it diagnosed or isolated to something in the passenger seat but didn't follow through with rectifying.

[jhubs139]

Completed a couple of small jobs yesterday. Took the buffing wheel and cutting compound to the headlights that had yellowed and gone hazy. Not 100% perfect as an outcome but the yellow tinge has gone and enough of the haziness has disappeared for me to be happy for now. Just to get the overspray of the cutting compound off the paintwork now!

I also changed the air filters to a pair of K&N panel filters. No pics of this but was about as straight forward as an air filter change can be. The air box is part of engine cover and pops off and on very easily. Not sure if there is any noticeable difference but is a change I like to do to my cars.

Next on the research list once the mechanical side of things are sorted will be a double din updated head unit/screen with Android Auto and Apple Car play. Does anyone have any experience of doing this upgrade on the CLK? I'm keen to retain the steering wheel controls.

Edited by jhubs139 on Sunday 24th April 11:25

[samoht]

My C55 gearbox is exactly the same, clunky 1st-2nd when cold. Have been to two specialists, had the fluid changed, and they can't suggest anything other than taking the box out and sending it to a automatic transmission specialist. Which doesn't seem worth the time/cost especially without knowing if they'll fix it, as it's not that bad.

Otherwise love the car, and can imagine the convertible version must be a nice thing.

[jhubs139]

samoht said:

My C55 gearbox is exactly the same, clunky 1st-2nd when cold. Have been to two specialists, had the fluid changed, and they can't suggest anything other than taking the box out and sending it to a automatic transmission specialist. Which doesn't seem worth the time/cost especially without knowing if they'll fix it, as it's not that bad.

Otherwise love the car, and can imagine the convertible version must be a nice thing.

That's useful to know. It is only an issue until the car gets up to temperature and then it is as smooth as silk. I think I will have the box serviced regardless for peace of mind but perhaps not spend too much time chasing the issue if that doesn't cure it.

Yeah it really suits being a convertible. Roof down the noise level is about right and it's definitely a cruiser rather than an out and out sports car.

[mwstewart]

samoht said:

My C55 gearbox is exactly the same, clunky 1st-2nd when cold. Have been to two specialists, had the fluid changed, and they can't suggest anything other than taking the box out and sending it to a automatic transmission specialist. Which doesn't seem worth the time/cost especially without knowing if they'll fix it, as it's not that bad.

Otherwise love the car, and can imagine the convertible version must be a nice thing.

Have you tried a reset of the TCU adaptions? My CLK55 did not have those symptoms.

The other cause can be incorrect oil level - either too much or too little. From memory the oil must be at the prescribed temperature when the level is checked. Temperature is read via diagnostics.

Edited by mwstewart on Sunday 24th April 19:14

[trevalvole]

Tommie38 said:

- Seats are controlled by an air pump in the boot. Issue is probably that. Breaks in the hoses also possible but obviously they wouldn’t be intermittent.

I'm surprised to hear that the seats are controlled by an air pump, as I've the related W203 with electric seats and there are only electrical connections to the seats.

On the subject of the SRS/seat electricals etc, I wonder if there is some general issue with the seat electrics or their connections, perhaps, with it being a convertible, the result of some moisture getting in?

[mwstewart]

The pneumatics are for the adjustable bolsters and lumbar. The actual movement of the seat is by electric motors.

It should be simple to diagnose.

[jhubs139]

mwstewart said:

The pneumatics are for the adjustable bolsters and lumbar. The actual movement of the seat is by electric motors.

It should be simple to diagnose.

Interesting to know. The lumbar and bolsters don't work at all at the moment so probably a separate issue to the intermittent seats in that case.

[mwstewart]

jhubs139 said:

Interesting to know. The lumbar and bolsters don't work at all at the moment so probably a separate issue to the intermittent seats in that case.

It will be. It isn't unusual to have issues with the pneumatic system, but obviously the electric side is higher up the priority list.

[jhubs139]

mwstewart said:

jhubs139 said:

Interesting to know. The lumbar and bolsters don't work at all at the moment so probably a separate issue to the intermittent seats in that case.

It will be. It isn't unusual to have issues with the pneumatic system, but obviously the electric side is higher up the priority list.

That's really helpful to know. I'll do some investigation (this is the exact knowledge I came here for).

[mwstewart]

trevalvole said:

...On the subject of the SRS/seat electricals etc, I wonder if there is some general issue with the seat electrics or their connections, perhaps, with it being a convertible, the result of some moisture getting in?

I agree with that. There is an outside chance that someone has removed the seat but did not reinstall it correctly, or somehow damaged the pneumatic and electrical connections. The connections are robust but worth checking.

[samoht]

That reminds me, I've recently had the occasional SRS warning light immediately after my passenger vacates the front passenger seat, assume it's the same sort of issue.

mwstewart said:

Have you tried a reset of the TCU adaptions? My CLK55 did not have those symptoms.

The other cause can be incorrect oil level - either too much or too little. From memory the oil must be at the prescribed temperature when the level is checked. Temperature is read via diagnostics.

I'm away from home currently, will look into TCU adaptations when I'm back, thanks a lot for the tip!

The first specialist definitely checked the level, they said that low oil which would expand as it warmed up could explain it. But they said it was fine.

Appreciate the tips on this as it's the only thing that slightly annoys about mine currently.

[jhubs139]

mwstewart said:

Have you tried a reset of the TCU adaptions? My CLK55 did not have those symptoms.

The other cause can be incorrect oil level - either too much or too little. From memory the oil must be at the prescribed temperature when the level is checked. Temperature is read via diagnostics.

Edited by mwstewart on Sunday 24th April 19:14

How do I reset the TCU adaptations? Is this a procedure I can do within the car or does it need to be plugged in? I remember doing the reset in my M3 for the SMG box quite regularly.