Component description for NOx sensor control unit - GF14.40-P-3024MM

ENGINE 276.9 in MODEL 204, 207, 212 (except 212.095), 218 with CODE 920 (Direct petrol injection with stratified charging) 

Shown: the exhaust system 

Location 

In every exhaust tract there is a NOx sensor with permanently attached NOx sensor control unit. The NOx sensors are screwed into the exhaust pipes. The NOx sensors control units are located on the underfloor.

Task 

The NOx sensors detect the NOx and the O₂ - concentration in exhaust after every NOx storage catalytic converter and passes this information to the NOx sensor control units in the form of voltage signals. These process the information and send it via drive train sensor CAN

(CAN I) to the ME-SFI [ME] control unit (N3/10).

Input and output signals 

The NOx sensors control units evaluate the following input signals and send the corresponding output signals:

• Direct input signals 
• CAN input signals from the ME-SFI [ME] control unit 
• CAN output signals to the ME-SFI [ME] control unit 

Direct input signals 

• circuit 87

CAN input signals from the ME-SFI [ME] control unit 

• Diagnosis requests

CAN output signals to the ME-SFI [ME] control unit 

• NOx concentration in exhaust
• O₂ concentration in exhaust
• Diagnostic data

Body 

Every NOx sensor (double chamber sensor with evaluation circuit) is inseparably connected via an 8-pin sensor line with the NOx sensor control unit.

An integral sensor heater which is controlled by the respective NOx sensor control unit ensures rapid readiness to operate of the NOx sensors.

Function 

The active ceramic probe bodies consist of many layers with two reaction chambers. The oxygen (O₂ ) in the exhaust is detected in the first chamber, as in an oxygen sensor.

To do this, a pump voltage is applied to the electrodes in the first chamber. This causes the O₂ molecules to be split into double charged oxygen ions and then pumped out of or into the first chamber (dependent on whether rich or lean exhaust gas is present) until a 450 mV voltage difference at the electrodes is reached. The oxygen concentration is calculated from the size of the required pump current "Ip1".

The nitrogen oxide is split at the earth electrode into nitrogen and oxygen in the second chamber if present. The oxygen is pumped out if the chamber again. The concentration of the nitrogen oxides in the exhaust is calculated from the resulting pump current "Ip2". The voltage signals from NOx sensors are transmitted to the respective NOx sensor control unit and processed there. The NOx sensor control units send the NOx and the O₂ concentration to the CDI control unit via drive train sensor CAN.

Using this information, the exhaust treatment can be monitored in stratified operation (lean-burn operation) of the engine and thus the NOx storage catalytic converter purging can be controlled.

The NOx sensors also recognize damage and "sulfur poisoning" of the NOx storage catalytic converters.

A desulfuring process can be initiated as a reaction by the ME-SFI [ME] control unit by increasing the temperature of the NOx storage catalytic converters.

Schematic function diagram of the NOx sensor (double chamber sensors) 

Designation	Unit	Values	Tolerance range	Remarks
LH NOx sensor control unit (N37/5), Right NOx sensor control unit (N37/6)
Supply voltage for control unit: minimum	V	6.0
Supply voltage for sensor heater: minimum maximum	V V	12.0 16.5
Power consumption	A	2.1
Power consumption	W	20		Maximum
Measuring range of the NOx concentration	ppm	0 - 500
Reverse polarity protection
Short-circuit resistance
Additional specific parameters
Special features
Flash capability/coding capability

	Wiring diagram for gasoline direct injection system control unit	N3/10 Vehicle connector model 204	PE07.08-P-2101-97FAF
		N3/10 Vehicle connector model 207	PE07.08-P-2101-97EAF
		N3/10 Vehicle connector model 212	PE07.08-P-2101-97DAH
		N3/10 Vehicle connector model 218	PE07.08-P-2101-97XAD