• The Forums are now open to new registrations, adverts are also being de-tuned.

ECU and Oxygen sensors failed at same time?

LeeC3003

New Member
Joined
Aug 7, 2014
Messages
3
Car
C230 2008
Hi All

Hoping someone can help with advice on a problem I have with my C230 Automatic 2008 W204. I am based in Singapore but from UK with a UK Spec car. As with everything here car costs are horrendous along with repair and even from the main dealer you can't get honest advice.

So my car while driving down a normal road lit up like a Christmas Tree on Saturday with every failure you can imagine on the dash with main message something like your car is Inoperable consult your dealer. The power drained off gradually and the car stopped in the middle of the road. Even after stopping and removing the key it wouldn't crank or restart, all messages remained.

Car was towed to the dealer and they just called me saying the ECU needs replacing as well as the for O2 sensors. I have two issues, I can understand the O2 sensors may have gone but why would this trigger the car to stop? the car has done about 60,000 miles. Also why would the ECU pack up at exactly the same time, just seems too convenient to me.

Does anyone have any ideas so I can look into this. I can't see why an 8 year old car with 60,000 miles would need a new ECU for a start.

Local prices they have quoted are about 3000GBP for a ECU and 2200GBP for the sensors which is crazy pricing.

Any help is much appreciated, Thanks in advance..
 
isnt it more like the O2 sensors are out of spec or on the way out, and the actual breakdown was caused by the ECU failing?
 
The W204 C class was introduced in 2007 and in the main enjoys the reputation of being a reliable car. https://en.wikipedia.org/wiki/Mercedes-Benz_C-Class#W204 Specifications varied according to different markets but the petrol engined 4 cylinder versions started as Kompressor versions of the well known M271 engine in different states of tune. These were later replaced by a turbocharged version in 2008. https://en.wikipedia.org/wiki/Mercedes-Benz_M271_engine
Due to the popularity of the diesel engine in the UK there were not many petrol engined models purchased in the UK so experience of them on UK forums is limited. They were far more popular in the USA so you might have better luck with your request for information on forums there??? I see you are from Singapore which I believe has a fairly humid climate- not a good thing for these electronic laden cars. It does sound as if your car has suffered a fairly catastrophic electric fault possibly due to an electrical short somewhere. What most people don't know is they have a series of fusible links [ non replaceable high current fuse type devices] that provide power to many of the cars main electrical systems from the battery [ bit like a computer power bus ]. If I was to guess it sounds as if one or more of these has blown due to a fault/short further down the line. This might show up as one of these car systems being "dead" While giving the appearance of total failure it often means that all that is required is replacement of the fusible link assembly together with fault that caused it to blow in the first place. I will try to find a link to post that describes the fusible links in more detail on the W204. PS these cars are complex bits of kit-- they need to be repaired by a garage familiar with the model and its systems and with the correct diagnostic equipment =Mercedes Star------ the general purpose "garage on the corner " however competent will not have the necessary expertise.
 
Last edited:
Thanks Graeme for all of the detailed info. Yes it is very humid here just frustrating when you pay a lot for a Mercedes which you expect to be reliable and unfortunately it has been anything but reliable.

It is in the Mercedes dealer garage at the moment and they say it has been diagnosed on their system which they charge you a 100GBP fee for.

If they have used the correct system as you say could it still be the fusible link issue? The problem here is nobody will go beyond looking at a screen and saying this is what the problem is and the prices they overcharge I do question. The dealership is renowned for overcharging and doing things not needed but most locals will never question and just say do it whereas I do question them..

Just a thought I had the brake warning light on before it happened, could this have caused the car to cutout for safety reasons? Just trying to come up with ideas before going back to the dealer... 4.5K GBP on a car that has to be scrapped in 2 years and cost 75K GBP second hand at 3 years old isn't worth it if I can avoid it... The Joys of Singapore car ownership !!!!

Appreciate your help and advice..
 
I am guessing here but I reckon the two faults the Mercedes STAR system brought up are unrelated. Highly unlikely that a defective lambda [O2] sensor would blow the engine ECU. The O2 sensor may have been defective for some time its just that Star has logged it as defective now. Turning to your other problem people use the term ECU very loosely. It may not refer to the engine ECU but to the unit that controls the ABS/ stability control. [THAT BRAKE WARNING LIGHT?] Its possible that a fault in that particular unit might cause the entire car to shut down for safety reasons?? The most common fault is a trivial one- the brake light switch assembly- which tells the ECU the brakes are being applied. Its a wear and tear item due to its continued use. Many people have such problems solved by simply replacing the switch. However at the other side of the world and without knowing exactly what your dealer said was wrong I can only speculate. Is there no reliable Singapore independent Mercedes workshop you could try for a second opinion?
 
Since you're in the same time zone as Australia, have you tried the dealership in Perth as an alternative to Singapore? - Obviously they can't look at the car, but they might have better pricing.

Although I've never lived in Singapore, I've got friends that have (and still do). - They say that most cars are just a status symbol, and Singaporeans that can afford them don't really care what it costs to keep them on the road.
 
Unless it's a particularly shoddy map, all a failed lambda sensor might do is put it in to limp mode (since it can't run closed-loop).

The car should still be able to run on the basis of the MAF and TPS inputs; it just might not run quite as smoothly (I suspect it will over-fuel slightly as that's safer than running lean).
 

Users who are viewing this thread

Back
Top Bottom