Boost pressure control, ME-SFI fault code description - AD07.61-P-4000-97M

		Boost pressure control
1	Fault code	P2001 Charge pressure too low (-)
	(Fault code according to OBD)	P20E2 Charge pressure too high (-)
2	Fault storage	After expiry of test duration and fault
	Actuation of engine diagnosis indicator lamp (EURO4) or CHECK ENGINE (MIL)	no activation
3	Checking frequency	Continuous
4	Checked signal or status	Charge air pressure value depending in the performance map (pressure conditions downstream/upstream of compressor) Values from the pressure sensor upstream of throttle valve actuator (B28/6) to pressure sensor downstream of air filter, for the right cylinder bank (B28/5).
5	Fault setting conditions
	Boost pressure too low/too high	Deviation from the performance map value to large
6	Check prerequisites	no fault in pressure sensor boost pressure control adapted
7		the closed throttle is closed at an excessively high boost pressure to protect the turbocharger. Causes for an excessively low boost pressure could be:  Leaky charge air ducting Charge air temperature greater than 70°C due to air in the low temperature cooling circuit or a fault in actuation of the charge air cooler circulation pump Boost pressure control pressure transducer (Y31/5) has a short circuit to minus or line discontinuity, boost pressure control pressure transducer is defective Hose line to pressure sensor upstream of throttle valve actuator (B28/6) leaky Deceleration air valve leaky due to cracked membrane (leak test) Turbocharger blocked or sluggish, e.g. due to a foreign object in the compressor housing. If a turbocharger stops then the boost pressure will fall over this unit. Boost pressure control valve (wastegate) does not close, e.g. due to a loose or bent control rod. If the boost pressure control valve on a turbocharger is hanging open then there complaint of a loss of performance when driving off. Air filter dirty Altitude or pressure sensor for ambient pressure in engine control unit defective Fuel grade inadequate (RON 98 required). Causes for an excessively high boost pressure could be:  Electrical line to boost pressure control pressure transducer (Y31/5) has a short circuit to positive Leaky or switched around hose lines between charge air cooler, boost pressure control pressure transducer and vacuum cell Boost pressure control valve (wastegate) jammed closed Control rods to the boost pressure control valves (wastegate) loose.

Fig 1: Boost Pressure Control Function Diagram

Courtesy of MERCEDES-BENZ USA

The input parameters for the boost pressure control are:

• Pressure values of pressure sensor downstream of air filter (B28/4 and B28/5)
• Pressure values from pressure sensor upstream of throttle valve actuator (B28/6)
• Charge air temperature, signal from charge air temperature sensor (B17/8)
• Load recognition from pressure sensor downstream of throttle valve actuator (B28/7)
• Ambient pressure (altitude correction), signal from pressure sensor in engine control unit
• Engine speed
• Coolant temperature
• Engaged drive mode
• Engine oil temperature
• Pressure drop in air filter, detection by pressure sensor downstream of air filter
• Exhaust gas temperature (from model calculation/performance map)
• Knock control active (maximum boost pressure only possible with RON 98)
• TWC damaging misfires identified.