Exhaust System Differential Pressure Sensor, Basic Function - GF49.20-P-2000A

Engine 256, 264 in model 167 

with code 598 (Gasoline particulate filter (OPF) with sensor system) 

Engine 260, 282 in model 118 

with code 472 (Gasoline particulate filter) 

Engine 260, 282 in model 177, 247 

with code 598 (Gasoline particulate filter (OPF) with sensor system) 

Engine 608, 654, 656 

All models (cars) 

Engine 656 

All models (off-road vehicles) 

Courtesy of MERCEDES-BENZ USA

Sample illustration of differential pressure sensor and temperature sensor on spark-ignition engine 

Courtesy of MERCEDES-BENZ USA

Sample illustration of differential pressure sensor at diesel engine 

Overview 

This document contains information on:

• General 
• Function 
  • Analog differential pressure sensor 
  • Digital differential pressure sensor 

General 

The particulate filter differential pressure sensor (1, 3) provides the pressure drop that is caused by the filter and the loading of the soot particulate filter.

The low-pressure exhaust gas recirculation differential pressure sensor provides the pressure drop that is caused by the low pressure exhaust gas recirculation tract (essentially the low pressure exhaust gas recirculation valve).

Depending on the exhaust system design, there are several differential pressure sensors installed:

• Particulate filter differential pressure sensor (1, 3) (gasoline and diesel engines)
• Low-pressure exhaust gas recirculation differential pressure sensor (diesel engines)

The measuring signal of the particulate filter differential pressure sensor (1, 3) is used in the control functions of the combustion engine control unit that serve for the proper regulation and monitoring of the soot particulate filter as part of the exhaust gas aftertreatment.

The measuring signal of the low-pressure exhaust gas recirculation differential pressure sensor is used by the control functions of the engine control unit that ensure proper control and monitoring of combustion.

The particulate filter differential pressure sensor (1, 3) is located in the area of the soot particulate filter.

The exhaust gas recirculation differential pressure sensor is located in the area of low-pressure exhaust gas recirculation.

The gas pressure lines coming from the sensor are connected either upstream or downstream of the soot particulate filter or the low-pressure exhaust gas recirculation at the exhaust pipe.

Function 

Analog differential pressure sensor 

The particulate filter differential pressure sensor (1, 3) consists of a piezoresistive pressure sensor element, electronics for signal amplification and a temperature compensation. All components are integrated in a silicon chip. The silicon chip is molded into the plastic housing. A protective gel protects the silicon chip against corrosion damage.

The pressure difference between the exhaust gas pressures acts on a piezoresistive pressure sensor element. A voltage is hereby generated that is amplified by the integrated silicon chip and is forwarded as a sensor signal to the combustion engine control unit.

The pressure upstream of the soot particulate filter is applied from one side at the pressure element in the particulate filter differential pressure sensor (1, 3). The pressure downstream of the soot particulate filter is applied at the other side. Once a pressure difference exists, the pressure element curves in the corresponding direction.

Digital differential pressure sensor 

The particulate filter differential pressure sensor (1, 3) consists of a plastic housing with two pressure connections that lead to two separate pressure chambers. A 3-pin MLK plug has been integrated in the housing as an interface to the engine wiring harness. For the attachment, a screw-on point is integrated in the plastic housing that is reinforced by a case-in metal sleeve.

There is a PCB with the sensor electronics located inside the sensor housing. There are two piezoresistive pressure measuring elements on the front of the PCB. The pressure measuring elements are positioned in the openings of the pressure measuring chambers.

The electronic circuit with amplifier (Application Specific Integrated Circuit, ASIC) for processing and outputting the measured pressure signals is located on the rear of the printed circuit board.

To protect the piezoresistive pressure elements against chemical damage due to exhaust gas, these are coated with a gel.

Two piezoresistive measuring cells in which two separate measuring chambers have been installed record the exhaust gas pressure at the respective sampling point.

The resulting voltage of the measuring cells is processed by the measuring circuit with an amplifier. The amplifier calculates the pressure differential from both independent pressure signals and converts this into a digital output signal (SENT).

The digital signal in the SENT format is transmitted to the combustion engine control unit via a wiring harness.