Engine Light On: The engine warning lights come on. In some cases, you may have more than one light. It is highly recommended to look into the issue fight away.
However, the engine warning light can come on due to plenty of reasons, so don’t rush to conclude that it’s coming on due to the NOx sensor problems. For those of you that have an engine code scanner, you should be able to detect whether it’s the NOx sensor causing your issues with an onboard reading from home. If you don’t have the analyzer, take your car to an experienced professional to help you with the diagnosis and analysis.
Here are some related codes for a BMW car
2AF2: 2B06; 2B09 nitric oxide sensor, Lambda linear
2AF4: 2B07; 2B0A NOx sensor, electrical
2AF6: 2AFB; 2B0B nitric oxide sensor, Lambda binary
2AF9: NOx sensor, NOx signal: coast mode check
2EAE: NOx sensor message missing (timeout)
30D6: nitric oxide sensor, plausibility
30D8: NOx sensor, Sensor damaged
30DA: NOx sensor, heating time
30DC: nitric oxide senor, heating
Other major symptoms can be fuel consumption going up and erratic idling.
Fuel Consumption Up: If the NOx sensor no longer operates as intended, it cannot send right information to the engine, the ECU is unsure how much fuel to provide to the engine. And due to this, the engine’s electronic brain assumes that your car is in the worst condition and enriches the fuel mixture to provide maximum power to the car.
Erratic Idle: In most cases, erratic idling is due to a faulty NOx sensor. Fuel injectors have to maintain a certain fuel flow into the combustion chamber for even idling, a task that the DME electronically manages.
When the NOx sensor is faulty, the starving and surging of the fuel results in uneven idling, therefore, if you have noticed that the car isn’t sticking to a given rpm, a faulty NOx sensor might be the reason.