Mercedes Benz W211 E280 CDI Saloon 2006 facelifted - Power steering changes from heavy to light mode

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Sun 23 Feb 2014 13:05
Mercedes Benz W211 E280 CDI Saloon 2006 facelifted - Power steering changes from heavy to light mode - parso

I have a 2006 (56 plate) facelifted Mercedes Benz E280 CDI saloon, which I have owned from new and has done 42000 miles.

I am experiencing a problem with the steering, where it is heavy when I start the car from cold in the morning, and remains at the same weight, however long I drive it for (20 mins, 1 hr, 2 hrs etc), until I stop the car, let it stand for 20 - 30 minutes and then, when I restart it, the steering is a lighter weight. It seems to need the engine to reach normal operating temperature before the switching off, leaving 20 mins and restarting routine will have any effect. If I start the car from cold, let it tick over for a couple of minutes, leave it for 20 mins and then restart it, the steering will be just as heavy as it is when started from cold.

The other interesting factor is that, in the summer, when the ambient temperature is about 20c or higher, when I first start the car, the difference between heavy and light is almost imperceptible, as the weight of the steering remains lighter the whole time.

Any suggestions would be greatly appreciated, as my Mercedes dealer has been completely bewildered by this problem.

Thank you.

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Mon 24 Feb 2014 12:06
Mercedes Benz W211 E280 CDI Saloon 2006 facelifted - Power steering changes from heavy to light mode - cws

First thing check the simple things - is the PAS fluid level correct or is it dirty/broken down, and needs changing? You'd hope that the dealer had checked these, but you can at least rule these out yourself.

If the fluid is all ok, then could be the pump failing - might have tight spots when it's running, which is causing the variances in feel/pressure. You may be able to get the pump rebuilt (but an MB main dealer will only want to sell you a new pump).

If the pump is ok, then it could be the steering rack - I think there's a sensor on the rack which controls the PAS fluid pressure ie the

pressure is lowered when the steering wheel is straight/rack isn't working - this may need replacing, but this would only show up via a diagnostic check/test. Again, do you know if these were checked by the dealer?

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