w203 54 2004 c220 cdi fault codes/ egr

[slik_sly]

My mates had his engine management light come on in his 2004 54 c220 cdi auto.

My basic OBD Code reader has brought up the following:

P0402 Exhaust Gas Recirculation Flow Excessive Detected
P0404 Exhaust Gas Recirculation Circuit Range/Performance
P0408 Exhaust Gas Recirculation Sensor B Circuit High

We have cleared the faults code and the only one to return is
P0404 Exhaust Gas Recirculation Circuit Range/Performance

From what i can guess there is a fault in the EGR system?

How would we go about diagnosing this?
I am pretty familiar with how BMW EGR systems work but Mercs are new to me.

Any help will be gladly appreciated

 

[htavs]

Hi, on the EGR Valve there is a removable plastic cover between the two bolts that fix it to the Manifold. You need to take the plastic cover off just use a thin flat head screw driver. Underneath it you will see the workings of the EGR Valve this sometimes over time gets clogged with soot use brake cleaner on it to clean it out and then once cleaned use a high melting point grease to lubricate it.

Start the car with the plastic cover off and get your mate to rev the car between idle and 3k on and off, you will see it work or not if the case may be. This may rectify your mates fault if not it may need a ‘good clean’ which will involve the removal of the EGR valve the EGR cooler and the Throttle housing, these can get caked up and can give false readings to the many different sensors.

If the matter persists then you may need to look at cleaning out the DPF or look at the DPFE sensor as all these factors work round the EGR performance all have to be working within their respective tolerances for the car to run efficiently if not it’s the LIMP mode!

You will see the DPFE sensor at the top left side behind the Air filter housing. This sensor will have 2 pipes coming into it which carry exhaust gasses which means there will be carrying a fair amount of soot so over time they may clog the sensor if not burn it out. This sensor works directly with the EGR valve as on these cars the EGR is electronic so one faulty sensor and its LIMP mode.

Hope this helps.