Component description for NOx sensor control unit - GF14.40-P-3024OMA
ENGINE 651.9 in MODEL 207, 212 (except 212.098/298), 218 with CODE U77 (Diesel Emission control BLUETEC (SCR)) without CODE 494 (US version) without CODE U42 (BlueTEC diesel exhaust treatment (SCR))
View of exhaust system on model 212.0 (with code (474) Particulate filter)
Location
The NOx sensor downstream of the diesel particulate filter is located in the exhaust pipe downstream of the diesel particulate filter (DPF) and the NOx sensor downstream of the SCR catalytic converter is located in the exhaust pipe downstream of the SCR catalytic converter. The NOx sensors control units are located respectively on the underfloor.
Task
The NOx sensors control units are supplied by the company "VDO Automotive AG". The NOx sensors detect the NOx and the O2 concentration in the exhaust downstream of the DPF and the SCR catalytic converter and forward this information to the NOx sensors control units in the form of voltage pulses. These control units process the information and transmit it via the drive train sensor CAN (CAN I) to the CDI control unit (N3/9).
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 CDI control unit
- CAN output signals to the CDI control unit
Direct input signals
- Terminal 87
CAN input signals from the CDI control unit
- Diagnosis requests
CAN output signals to the CDI control unit
- NOx concentration in the exhaust
- O2 concentration in exhaust
- Diagnostic data
Body
Every NOx sensor (double chamber sensor with evaluation circuit) is inseparably connected via an 8-pin signal line with the respective 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) is detected in the exhaust in the first chamber as in the case of 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 (depending 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 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 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.
Schematic function diagram of the NOx sensor (double chamber sensors)
| Wiring diagram for AdBlue® control unit | N118/5 Model 207 | PE14.40-P-2101-97EAA | |
| Model 212 (except 212.098/298) | PE14.40-P-2101-97DAB | ||
| Model 218 | PE14.40-P-2101-97XAB |