Component description for nitrogen oxides control unit with NOx sensor - GF14.40-P-3023OG

ENGINE 642 in MODEL 212 up to 8/31/14, 218 up to 8/31/14 with CODE U42 (BlueTEC diesel exhaust treatment (SCR)) 

ENGINE 642.8 in MODEL 207, 212 as of 9/1/14, 218 as of 9/1/14 with CODE U77 (Diesel Emission control BLUETEC (SCR)) 

Shown on model 212.024 from the right 

Fig 1: Nitrogen Oxides Control Unit - Shown On Model 212.024

Courtesy of MERCEDES-BENZ USA

Location 

The NO _X sensor is screwed into the exhaust pipe downstream of the diesel particulate filter (DPF). The nitrogen oxides No _x control unit is connected inseparably with the NO _x sensor and located on the underfloor.

Shown on model 212.024 from the front 

Fig 2: SCR Catalytic Converter - Shown On Model 212.024

Courtesy of MERCEDES-BENZ USA

Location 

The NO _x sensor is screwed into the exhaust pipe downstream of the SCR catalytic converter. The nitrogen oxides control unit downstream of SCR catalytic converter (N37/8) is inseparably connected with the NO_x sensor or sensor NO _x and located on the underfloor.

Task 

Nitrogen oxides control units are supplied by the company "VDO Automotive AG".

The NO _x sensors detect the NO _X and the O ₂ concentration in the exhaust downstream of the DPF and SCR catalytic converter and pass this information on to the 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 nitrogen oxides control units evaluate the following input signals and send the corresponding output signals:

• Direct input signals 
• CAN input signals from the CDI control unit via the drive train sensor CAN 
• CAN output signals to the CDI control unit via the drive train sensor CAN 

Direct input signals 

• Terminal 87

CAN input signals from the CDI control unit via the drive train sensor CAN 

• Diagnosis requests

CAN output signals to the CDI control unit via the drive train sensor CAN 

• NO_X concentration in the exhaust
• O₂ concentration in exhaust
• Diagnostic data

Body 

Every NO _X sensor double chamber sensor with evaluation circuit) is inseparably connected via an 8-pin signal line with the respective nitrogen oxides control unit.

An integral sensor heater which is controlled by the respective nitrogen oxides control unit ensures rapid readiness to operate of the NO _X sensors.

Fig 3: Nitrogen Oxides Control Unit

Courtesy of MERCEDES-BENZ USA

Function 

The active ceramic probe bodies consist of many layers with two reaction chambers. The oxygen (O ₂ ) 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 O ₂ 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 the NO _X sensors are transmitted to the respective nitrogen oxides control unit and processed there. The nitrogen oxides control units send the NO _X and the O ₂ concentration to the CDI control unit via the drive train sensor CAN.

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

Fig 4: NOx Sensor Function Diagram

Courtesy of MERCEDES-BENZ USA