ML 270 Running in 'Limp' mode

[richbrowne]

Hi,

I own an ML 270 and it has started to intermittently run in ECU 'Limp' mode. The disc pad warning light and brake fluid level lights started to come on (fluid level goes down slightly with disc pad wear) with the 'usual' beep from the dashboard to indicate the issue.

Approx. 20 miles after the pad warnings, power was substantially reduced and it will not exceed a certain speed.

I initially thought this 'Limp' mode was due to the disc pad wear but I have since been told that this does not induce 'Limp' mode.

Does anyone know what could be causing this please?


Thanks in advance.


Rich.

 

[richbrowne]

I have also posted this in the 'ECU' section as I was unsure what category this should be posted in?

 

[Mrtibbs]

Hi Rich
I had a fault with my ML270 when I went to test drive it, prior to buying, and it was diagnosed as a faulty fuel injector. The injector was replaced and it has been fine ever since (only a few weeks.... but long enough I think).
I wonder if yours is suffering the same problem? During my test drive I had a low fuel and low brakes warning appear momentarily on the dash, then they went out but the fault stayed, totally gutless.....
It may be worth sticking some injector cleaner down its throat as it only costs about a fiver and going for a decent run. It will be cheaper than having the car put on a diagnostic system and to be honest I would think it will do it good even if that is not the fault.
Maybe someone else has a better idea?
HTH

Keith

 

[richbrowne]

Hi Keith,

The ML problem is a funny one. I do believe that the disc pads need replacing as the warning lights and bleep occur regularly when the brakes are applied (I have performed a best endeavours visual inspection through the wheels and the front pads are low, but nowhere near the metal yet).

The ML mostly stays in 'Limp' mode but does partly/fully come out of it now ang again?

 

[Xtractorfan]

The most probable cause for the limp mode is normally the MAF..or air flow meter.. The brake problem is as you suspect due to pads needing replacing.

 

[richbrowne]

The most probable cause for the limp mode is normally the MAF..or air flow meter.. The brake problem is as you suspect due to pads needing replacing.

Thanks for the information. Is it possible to diagnose this by checking the ECU error codes?

 

[television]

I would check the MAF by unplugging it and trying the car,ignore the idle if its rough or lumpy

 

[richbrowne]

I would check the MAF by unplugging it and trying the car,ignore the idle if its rough or lumpy

Thanks. Don't suppose you can point me to where this unit is placed on the ML 270 please?

 

[television]

Its 14 in the link

http://www.detali.ru/cat/oem_mb2.as...GM=716.644&CT=M&cat=21T&SID=09&SGR=015&SGN=01

 

[richbrowne]

Its 14 in the link

http://www.detali.ru/cat/oem_mb2.as...GM=716.644&CT=M&cat=21T&SID=09&SGR=015&SGN=01

Thanks.

 

[richbrowne]

Thanks for all your answers guys.

I had the ML serviced today and recommended that the MAF sensor was changed. Apparently the ECU pointed towards this as failing anyway and following the installation of a new sensor, it is back to how it was before.

I say 'back to how it was' because it was and still is, down on turbo power/boost for some reason. Possible issues have been pointed towards the inlet manifold or the waste gate vacuum.

Does this sound right?

 

[Hertfordshire Merx]

I would firstly test the intercooler boost system for split hoses as this is common, you will hear these under hard acceleration as a high pressure air escaping.

This fault also brings up suspect readings the mass air flow sensor as the amount of air is not being regulated if a pipe is split. Easy to get caught out on, and can be a costly mistake by whoever diagnosed it!!

Have had turbo waste gates sticking in the open position so no boost builds up. The above faults will cause the engine to not rev over 3000rpm while under load. Then it will go into limp home mode after two similar drive cycles with the same fault. Have the running vacuum checked should be 700mbar or just under, that would give you a good sign to see if there is a vacuum leak. if you have then its worth substituting the turbo transducer to see if the fault goes.

Incidetally, Mercedes have just released a new service operation recall with regards to the actuator rod on the turbos for V6 diesels. They must be chrome plated to prevent corrosion, if not the rod must be replaced. Have heard tales of dealers replacing the whole turbocharger units when only the rod is required to be replaced in the working instructions and Mercedes are reclaiming the costs back from the dealers!

 

[richbrowne]

I would firstly test the intercooler boost system for split hoses as this is common, you will hear these under hard acceleration as a high pressure air escaping.

This fault also brings up suspect readings the mass air flow sensor as the amount of air is not being regulated if a pipe is split. Easy to get caught out on, and can be a costly mistake by whoever diagnosed it!!

Have had turbo waste gates sticking in the open position so no boost builds up. The above faults will cause the engine to not rev over 3000rpm while under load. Then it will go into limp home mode after two similar drive cycles with the same fault. Have the running vacuum checked should be 700mbar or just under, that would give you a good sign to see if there is a vacuum leak. if you have then its worth substituting the turbo transducer to see if the fault goes.

Incidetally, Mercedes have just released a new service operation recall with regards to the actuator rod on the turbos for V6 diesels. They must be chrome plated to prevent corrosion, if not the rod must be replaced. Have heard tales of dealers replacing the whole turbocharger units when only the rod is required to be replaced in the working instructions and Mercedes are reclaiming the costs back from the dealers!

Hi MSH,

Thanks very much for the information. The car was only serviced yesterday and so far has not entered limp mode. However, from what you say it is quite possible it will enter the cycle you have detailed again if there is a problem with the vacuum. I'll watch out for this, thanks.

Regarding the recall, I had not heard of this; presumably because mine now gets serviced by an independent. Would mine require the recall please? How can I check, by ringing my local Merc garage and providing chassis number or maybe just reg I guess?

Thanks again, you have been most helpful.

 

[Hertfordshire Merx]

Yes by all means give your local dealer a call I believe the recall number is something like P186 reference the new ones. Yours might not be influenced by this.

Hope they're helpful....

 

[BlackC55]

Is it a 163 or 164?

 

[richbrowne]

Is it a 163 or 164?

Ah, I guess this is part of the chassis number? In that case it's a 163. Why?

 

[Hertfordshire Merx]

Check the boost system black rubber pipe which is attached to the intercooler on the near side (left-hand-side if you were sat in the drivers seat), as I have replaced a few of these for a split. May be oily on the outside and this would be an indication of a leak there.

 

[richbrowne]

Check the boost system black rubber pipe which is attached to the intercooler on the near side (left-hand-side if you were sat in the drivers seat), as I have replaced a few of these for a split. May be oily on the outside and this would be an indication of a leak there.

Thanks MSH, much appreciated.

Is there a need to remove anything to get to this pipe please or is it fairly obvious?

 

[Hertfordshire Merx]

Yes you may need to remove the front most section of the undertray or get a decent torch and have a good look from underneath. Taking the undertray off is favourite though for a thorough inspection.

 

[richbrowne]

Yes you may need to remove the front most section of the undertray or get a decent torch and have a good look from underneath. Taking the undertray off is favourite though for a thorough inspection.

Thanks HM.