Alex Crow
Senior Member
- Joined
- Jul 9, 2009
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This was a long long story, but I will try to keep it short.
The car - 2005 E220 Cdi
The problem - frequent and consistent 'limp home', in conjunction with the code P2355-002
The fault would always occur at a cruising speed of around 70 mph
The above is the only fault code logged, and translates as "EGR malfunction, EGR air flow is too low" (which means airflow measured at the MAF sensor is too high).
A read out of the snap shot data shows EGR control at max (95%), and MAF sensor air flow still too high.
Previous work by several other garages has covered just about everything you can imagine, including: replacement turbo, replacement inlet manifold, replacement EGR valve, replacement airmass meter, checking intake and exhaust systems for leaks and/or blockages, having engine ECU tested by ECU repair specialists, checking EGR passages for blockage, having software update to 2007 version.
Note that this is by no means an exhaustive list.
This job took some considerable time to diagnose, but I will cut to the end.
EGR function was always OK at idle, and the control of the EGR valve was verified on roadtest - see attached thumbnail for an example of the PWM wave form. The actual EGR function was fault free.
The inlet manifold flap control was another story however, and it was found that the ECU was not regulating the flaps at all. This was the key to the fault condition, at the cruising speed the flaps should have been closed, but because they were open more air was being drawn in than expected, and becuase this was during EGR operation (yes, at 70mph) the fault code was being logged in relation to EGR function. On close inspection it was found that the ECU was not providing a correct PWM wave form, with either no amplitude, or when there was amplitue the signal was just 'noise'. See the second and third pictures.
Interestingly the ECU was not logging any manifold flap related fault codes, even with the actuator disconnected!
So a new ECU needed, but that was not what we did!..........................guess what the remedy was, over to you.
The car - 2005 E220 Cdi
The problem - frequent and consistent 'limp home', in conjunction with the code P2355-002
The fault would always occur at a cruising speed of around 70 mph
The above is the only fault code logged, and translates as "EGR malfunction, EGR air flow is too low" (which means airflow measured at the MAF sensor is too high).
A read out of the snap shot data shows EGR control at max (95%), and MAF sensor air flow still too high.
Previous work by several other garages has covered just about everything you can imagine, including: replacement turbo, replacement inlet manifold, replacement EGR valve, replacement airmass meter, checking intake and exhaust systems for leaks and/or blockages, having engine ECU tested by ECU repair specialists, checking EGR passages for blockage, having software update to 2007 version.
Note that this is by no means an exhaustive list.
This job took some considerable time to diagnose, but I will cut to the end.
EGR function was always OK at idle, and the control of the EGR valve was verified on roadtest - see attached thumbnail for an example of the PWM wave form. The actual EGR function was fault free.
The inlet manifold flap control was another story however, and it was found that the ECU was not regulating the flaps at all. This was the key to the fault condition, at the cruising speed the flaps should have been closed, but because they were open more air was being drawn in than expected, and becuase this was during EGR operation (yes, at 70mph) the fault code was being logged in relation to EGR function. On close inspection it was found that the ECU was not providing a correct PWM wave form, with either no amplitude, or when there was amplitue the signal was just 'noise'. See the second and third pictures.
Interestingly the ECU was not logging any manifold flap related fault codes, even with the actuator disconnected!
So a new ECU needed, but that was not what we did!..........................guess what the remedy was, over to you.
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