Component description for NOx sensor control unit

P14.00-2139-75

Location

The NOx control units are screwed onto the underfloor. The NOx sensors are screwed into the exhaust system.

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 pass this information onto 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

P14.40-2334-01

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) 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 (depending on whether rich or lean exhaust 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.

P07.04-2541-76