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Matt, Engineer
Category: Mercedes
Satisfied Customers: 21270
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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, 2001 c240 looses power momentarily when driving on

Customer Question

Customer: ***** *****
JA: Thanks. Can you give me any more details about your issue?
Customer: 2001 c240 looses power momentarily when driving on highway, but then recovers without stalling completely. It is intermiten. happens once in a while.
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Submitted: 1 year ago.
Category: Mercedes
Expert:  Matt replied 1 year ago.


I'm assuming that this is the petrol 2.6 ltr six cylinder engine ?

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance - Also replace the spark plugs if any of them fail this checklist:

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V

Customer: replied 1 year ago.
My car is NOT a petrol engine
It is a c240, 6 cylinder, 2.6L Injected Gasoline engine.
Expert:  Matt replied 1 year ago.

Hello Ted

petrol is gasoline chap ( the english term)

so my original advice still stands

let me know how you get on and get back to me on this post

Customer: replied 1 year ago.
Let me repeat the problem (Syndrome).
While driving at highway speeds, the car looses power (as if the engine cuts out) for a couple of seconds, but then it turns back on and runs normally. When this happens, the ESP light comes on and it stays on until the next time the car is turned off and restarted, at which time the ESP is no longer on. As I said, this happens during highway driving. However, one time it did it at around 25-30 mph as I was leaving the gas station where I had just gotten off the freeway , refueled, and was trying to get back on the freeway. My wife drives the car around town and it has never happened around town. When it first did it, about a year ago, my wife saw the ESP light and took it to the mechanic who read the codes and thought that the gas pedal sensor may be causing the ESP to come on. He probably thought that the ESP was the cause. After I have been driving the car to get a better feel for the syndrome, I believe that the ESP is not the cause, but the symptom. In other words, the ESP comes on because the engine cuts out, not the other way around. I tend to agree with you that the CPS may have an intermittent problem. But what makes me wonder is that I read online that other people who have bad CPS, some times they can not start the car. We never had that problem. The CPS in our car always senses the crank position correctly during starting up. It never fails to start or run properly at low speeds around town.
I can take it to our mechanic and replace the CPS but I would like to have higher level of confidence that the CPS is likely the problem. What do you think?
Thanks for listening. Let me know what you think.
Expert:  Matt replied 1 year ago.


thanks for the extra information as you have the ESP light on then

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

However with ABS systems 99% of the time its a problem with one of the wheel speed sensors and I'd first check the connections at all four corners first for any signs of corrosion or chafed wiring.

The sensor is located in the wheel hub so you'll have to remove each wheel in turn to inspect them all.

Also check that the toothed wheel that the sensor points to is clean and free of any debris.

you can check each sensor's function by plugging the two output wires into an AC voltmeter and spinning the wheel quite quickly, you should get a voltage signal that increases with rev's.

Its possible that the fault is only a bad connection to one of the wheel sensors.

This may be remedied by removing each wheel in turn and unplugging each sensor and cleaning the contacts with a squirt of electrical contact cleaner. Then refitting.