Diagnostic System Description

All BMW vehicles with the Motronic M1.1 ignition and fuel injection system are equipped with a self diagnostic system. In the event of a malfunction in the system, circuit information will be stored in an internal memory. Intermittent failures are stored with a record of the failure frequency. The M1.1 control unit can store up to 5 malfunctions at the same time and will give priority to those items which can cause the vehicle to exceed exhaust emission standards (in the theoretical case that more than 5 problems should occur at the same time).

In addition to being stored in memory, an emissions related failure will cause an indicator light ("CHECK ENGINE") to be illuminated on the instrument cluster. The information collected in the M1.1 control unit memory can be displayed on the BMW Service Tester. The malfunctioning component or circuit is identified together with the proper repair. Additional information is given on ambient conditions when the failure occurred. Generally two of the following conditions are displayed: engine rpm, engine load, engine temperature, ambient temperature, vehicle speed or battery voltage.

The following systems/components are those which, when detected as malfunctioning, will cause the "CHECK ENGINE" light to come on:

- Airflow Meter

- Lambda Control System

- Engine Temperature Sensor

- Throttle Valve Switch





When one or more of these systems/components malfunction while driving, the "CHECK ENGINE" light will be illuminated continuously. These failures can be displayed by special flash codes of the "CHECK ENGINE" light with the ignition key in position 2; three seconds after having put the ignition key into position 2, the following flash codes related to specific malfunctions can be displayed:

If, for example, the engine temperature sensor and the airflow meter should have failed in this sequence, you will read after 3 seconds the 3-flash code, after another 3 seconds the 1-flash code, then after another 3 seconds the "CHECK ENGINE" light will be on continuously.

Note:
The 4-flash code will only be displayed when all the following conditions occur at once:

- closed throttle valve switch;

- engine speed above 1,000 rpm; and

- load signal from airflow meter, i.e. flap not in closed position.

After having performed the repair, the failure memory can be cleared by punching in a special code (999) in the Service Tester. Failures can also be erased from memory automatically with the 5th engine start after the repair has been performed. Intermittent malfunctions in memory are cleared no later than the 10th engine start.

Note:
The flash code is not a substitute for the BMW Service Tester and a thorough troubleshooting procedure. It is only helpful as a quick and rough predetermination of some possible failure sources.

When there is no malfunction stored, the "CHECK ENGINE" light will be on continuously with the ignition key in position 2 for bulb checking. The light goes out when the engine is started.

NOTE:
If the "CHECK ENGINE" light is illuminated during driving and the 2-flash code is displayed in ignition key position 2, indicating a problem in the Lambda Control System, this does not mean necessarily, that the oxygen sensor is defective. The Lambda Control System flash code will also be displayed when the Lambda Regulation has reached its programmed thresh holds under certain circumstances with, for example, a defective purge valve. In this particular case a replacement of the oxygen sensor would not cure the problem.

As opposed to malfunctions of the airflow meter or coolant temperature sensor when the "CHECK ENGINE" light comes on immediately, it might take the Lambda System up to 3 minutes of engine running time before a malfunction is displayed by the "CHECK ENGINE" light.

In the case of an intermittent problem, it is possible that the failure memory is cleared by the 10th engine start before there is an opportunity to connect the engine to the BMW Service Tester. If this should happen, test drive the car under similar conditions as stated by the customer. The malfunction will then be restored.