Component description for NOx sensor control unit - GF14.40-P-3024MRA
Engine 274.9 in model 205 with code 920 (Direct petrol injection with stratified charging)
Engine 274.9 in model 253 with code 920 (Direct petrol injection with stratified charging)
View of vehicle from below on model 205.0
Location
In every exhaust system there is a NOx sensor with permanently attached NOx sensor control unit. The NOx sensor is screwed into the exhaust pipe. The NOx sensor control unit it located on the underfloor.
Tasks
The NOx sensor records downstream of the NOx storage catalytic converter the NOx and O2 concentration levels in the exhaust and routes this information in the form of voltage signals to the NOx sensor control unit. This processes the information and sends it via the drive train sensor CAN (CAN I) to the ME-SFI [ME] control unit (N3/10).
Input and output signals
The following input signals are evaluated by the NOx sensor control unit and appropriate output signals are emitted:
- 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
- Terminal 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 the exhaust
- O2 concentration in exhaust
- Diagnostic data
Body
The NOx sensor (double chamber sensor with evaluation circuit) is inseparably connected via an 8-pin signal line to the NOx sensor control unit.
An integrated sensor heater which is controlled by the NOx sensor control unit ensures rapid operational readiness of the NOx sensor.
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 broken down into double charged oxygen ions and for them to be pumped out of or into the first contact cavity (depending on whether richer or leaner 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 ground 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 the NOx sensor are sent to the NOx sensor control unit and processed there. The NOx sensor control unit sends the NOx and O2 concentration levels over the drive train sensor CAN to the ME-SFI [ME] control unit.
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 sensor also recognizes damage and "sulfur poisoning" of the NOx storage catalytic converter.
A desulfuring process can then be initiated by the ME-SFI [ME] control unit by increasing the temperature of the NOx storage catalytic converter.
Schematic function diagram of the NOx sensor (double chamber sensors)
| Wiring diagram for gasoline-DI control unit | N3/10, vehicle-side | PE07.08-P-2101-97FBJ |