Workshop Hints

Workshop Hints


Before any service work is performed on any fuel system related component, always adhere to the following:

^ Observe relevant safety legislation pertaining to your area.
^ Ensure adequate ventilation.
^ Use exhaust extraction system where applicable (alleviate fumes).
^ DO NOT SMOKE while performing fuel system repairs.
^ Always wear adequate protection clothing including eye protection
^ Use caution when working around a HOT engine compartment.
^ BMW does not recommend any UNAUTHORIZED MODIFICATIONS to the fuel system. The fuel systems are designed to comply with strict Federal Safety and Emissions Regulations. In the concern of product liability, it is unauthorized to sell or perform modifications to customer vehicles, particularly in safety areas.





The Malfunction Indicator Light can be diagnosed with an aftermarket Scan Tool that allows Technicians without BMW Special Tools or Equipment to Diagnose an emission system failure. With the use of a universal scan tool, connected to the "OBD" DLC Located in the driver's side left lower instrument panel area) an SAE standardized DTC can be obtained, along with the condition associated with the illumination of the "Malfunction Indicator Light". Using the DlSplus or GT1, a fault code and the conditions associated with its setting can be obtained prior to the illumination of the Malfunction Indicator Light.

Misfire Detection

Testing the Oxygen Sensor should be performed using the DlSplus Oscilloscope from the Preset Measurement List. The scope pattern should appear as below for a normal operating sensor.
If the signal remains high (rich condition) the following should be checked:
^ Fuel Injectors
^ Fuel Pressure
^ Ignition System
^ Input Sensors that influence air/fuel mixture
^ Engine Mechanical

If the signal remains low (lean condition) the following should be checked:

^ Air/Vacuum leak
^ Fuel Pressure
^ Input Sensor that influence air/fuel mixture
^ Engine Mechanical


NOTE: A MIXTURE RELATED FAULT CODE SHOULD BE INVESTIGATED REST AND DOES Not always INDICATE A DEFECTIVE OXYGEN SENSOR!

Check Filler Cap

After refueling and switching the ignition ON, the ECM detects a fuel level increase. When the ignition is switched OFF, the ECM activates the DM TL for a brief test to check the filler cap. If the filler cap was not properly installed; when the vehicle is started and driven at a speed >10 Km/h, the "Check Filler Cap" light will illuminate for 25 seconds (and then go out)
The second time the ignition is cycled OFF, the DM TL is activated to test the filler cap. If loose; when the vehicle is started and driven at a speed >10 Km/h, the Check Filler Cap light will be illuminated for 25 seconds (and then go out).
If the filler cap is properly secured, the Malfunction Indicator Light will not be illuminated and a fault code will not be stored in the ECM.
The third time the ignition is cycled OFF, the DM TL is activated to test the filler cap. If loose; a Large Leak fault code is stored in the ECM. The Malfunction Indicator Light will be illuminated the next time the engine is started.