Replacing of NOXEM 402. Introduction


The procedure of replacing the NOx emulator is very simple and takes 10 to 15 minutes.

After replacing the NOx emulator, several service procedures have to be performed.

  1. Clearing of adaptations of the NOx sensor. This procedure has to be performed as prescribed by BMW AG (in this case it’s the replacement of NOx emulator instead of the sensor). The NOx sensor reports to the engine management system several important parameters (content of oxygen in the exhaust, content of NOx, etc.), the engine management system processes the information and evaluates if the sensor readings are reliable and correct. It is critically important to update the “profile” of the sensor after replacement.
  2. Renewing of the NOx catalytic converter’s profile. The engine management system monitors the status of a NOx catalytic converter. Data on its short-term poisoning (with sulfur) and long-term deterioration are stored in the engine management unit. The engine management unit allows only long-term performance deterioration – this is self-explanatory. After replacing the catalytic converter the engine management unit has to be “informed”, that the catalytic converter is replaced. Otherwise, the new catalytic converter will not be used, because the engine management unit will be sure, that the catalytic converter is still damaged. This procedure also is intended in regulations from BMW AG as a service procedure.
  3. Re-adaptation of the engine. If the car has been driving for a while with a defective NOx system, the performance of the engine has been disturbed. The engine has used only one injection mode: Homogeneous injection (actually – emergency mode) from three possible modes, many service procedures (measuring of injector’s performance – leakage and reaction; equalization of the cylinder’s mechanical and chemical efficiency, etc.) are also been disturbed. After installation of the NOx emulator, the engine should be re-adapted: the old adaptations need to be cleared and the new ones – created.

To perform all service procedures, you will need INPA for F series (recommended) or ISTA D/+: software, well known to each BMW enthusiast.


Installing of NOXEM 402: replacement and service procedures


After the repair, we highly recommend performing a driving session to be sure DME renewed the Stratified charge as described here.


Note. 12C401 Plausibility: signal activity too low. This error message doesn’t relate to any malfunction of NOXEM. If 12C401 appears regularly, it’s a confirmation about the increased usage of Homogeneous injection mode. The cause of this situation could be: poisoned NOx converter; reduced efficiency of CO converters; leaking injectors; misfiring, etc. For more information please read here.


Important! For all owners of the N43/53 series engine (and N52/54/55 as well), we are recommending to purchase an ELM327 OBD diagnostics adapter. This is a cost-effective (starting from 3 EUR) solution with different connection (Bluetooth; Wifi; USB) option. With this adapter, you will see ignition quality (misfire counters) for each cylinder. If your engine has problems with ignition (partially damaged ignition coil, leaking injector, etc.), the situation may become worst when the Stratified charge will be re-enabled. The burning of a lean mixture requires the maximal power of spark, even the smallest current leakage or incorrect fuel beam can provoke misfires. With ELM327 adapter you will determine misfiring cylinder within seconds!

Detailed information here.