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Did you know that in 2015 the Mercedes C class was voted the overall World Car of the Year.  Wow.  That is some achievement.  Overall World car of the YEAR!  This title is not given lightly.  It’s an assessment made by 72 jurors including some of the top names in the motoring industry.  

And if you are a C Class owner, you will also know that the premium brand has a certain ‘something’ that keeps you as a Mercedes owner.  And it goes without saying that all vehicles, even premium German brands, require regular servicing and maintenance to make sure that they perform at their best.

So when Mr G brought his Mercedes C220 into our Newbury garage with an issue, our Mercedes specialist technicians got straight to investigating and diagnosing the problem.  Here at Fergies, we pride ourselves on making sure our clients get the best from their vehicles, and this includes a complete investigation to get to the root cause of the problem.

Our 15 step diagnostic evaluation makes sure that we can get to the root cause of the fault and, in turn, give the client a first-time fix every time.  And as your local Mercedes garage, our team use recommended manufacturer guidelines, making sure the integrity of your premium vehicle is maintained, just as Mercedes intend.

Mr G advised us that he had an Engine Management Light (EML) showing on his dashboard, highlighting a fault within the Engine Control Unit (ECU).  There was also an AdBlue warning showing.

The client advised that he had topped up the AdBlue within the C220, but he had ended up overfilling the system.  But what Mr G didnt know was that there is a risk of further damage if you overfill your AdBlue system.  The sophisticated system relies heavily on having everything working within the correct levels.

So our team of Mercedes specialists took the C220 from Mr G and got to work on completing a full visual inspection, followed by our 15 step diagnostic evaluation.  Having looked over the engine from all angles, we couldn’t see anything immediately wrong, so we started the evaluation with a full scan of the vehicle’s serial data.


Within our Newbury Mercedes garage, we accessed the vehicle serial data and found the fault code:

  • P140300 – The control unit AdBlue has a malfunction

Armed with the serial data, our Mercedes specialist technicians accessed the AdBlue pump and started to check the system’s wiring.  They found that there was no power going into the AdBlue module, so they began stripping back the wiring to locate the defect.  The team found that the main loom had rubbed completely through, which had caused water contamination and some serious corrosion to the power wire. The wiring had to be replaced entirely and re-insulated, something we can do onsite at Fergies.

Mercedes C220 adblue fault    

Mercedes C220 adblue fault

Whilst the technicians were working on the AdBlue system, they had also noticed a problem with the level sensor.  The client had already told us that he had managed to overfill the system, which shouldn’t happen with the system working on an ultrasonic sensor system.  But our knowledge and experience have taught us that if you overfill the AdBlue system, the ultrasonic sensor cannot check the level and therefore causes misinformation within the vehicle’s systems.

So we drained the AdBlue tank system then re-filled the tank to the correct level. With the AdBlue level at the correct level, we took the C220 for a road test and confirmed that the Engine Management Warning light had gone and the Mercedes was back to being a fun, reliable vehicle.


With the AdBlue system put back together and the road test completed, our team of Mercedes specialist technicians gave the C220 a final check over and handed the car back to Mr G.

The client was happy that he had his car back within 24 hours.  Fergies had given him that first-time fix and therefore saved him the stress and money of repeated repairs.  Everything was explained in detail to Mr G so that he was fully aware of what was going on through the repair, and therefore he knew he wouldn’t experience unnecessary costs.

This transparent approach is key to our business at Fergies, and we make sure that our clients are fully involved in the process of maintaining their vehicle and never hit with any unexpected charges.

If you are a Mercedes owner and want to enjoy the reliability of your vehicle, contact Fergies today and let our team of Mercedes specialists look after your car, giving you peace of mind and great value for money.

Call us today on 01635 778002 for your Mercedes servicing and repairs.

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