B3984 BMW Fault Code

Description:

Catalytic converters must be warm before they can work properly. On a cold start the PCM provides a rich mixture to keep the cold engine running.
All that extra fuel goes into the catalytic converter. But the exhaust isn't very hot, because, ah, the engine is pretty cold. GM has employed several strategies to fire up the catalytic converter quicker and reduce cold start emissions. One way is to use a secondary air pump that pumps outside air directly into the catalytic converter.

B3984 Code Symptoms :

While fuel economy was increased, acceleration was seriously compromised, and the loss of engine vacuum led to a dangerous loss of braking assist when the B3984 code system was in four-cylinder mode. In addition to these issues, while the company proposed a hydraulically controlled system that could be switched from within the car, the version they implemented had to be manually changed in the engine compartment using hand tools.

Diagnosis And Repairing B3984

Parts or components should not be replaced with reference to only a B3984 DTC. The vehicle service manual should be consulted for more information on possible causes of the fault, along with required testing.

How to fix B3984 code ?

• Air fuel ratio (A/F) Sensor 1 Bank 1 harness is open or shorted
• 1Camshaft Position Sensor circuit poor electrical connection
• Camshaft Position Sensor harness is open or shorted
• Open VPWR circuit