Ignition sensors (Motronic system) - check and renewal

Note: Some models are equipped with a TDC sensor mounted on the front of the engine. This sensor is strictly for the BMW service test

unit, and is not part of the Motronic ignition system.

Speed and position sensors

Check

1 Locate the two electrical connectors for the sensors (see illustrations). The grey connector is for the position sensor, and the white connector is for the speed sensor.

2 Using an ohmmeter, check the resistance between terminal 1 (yellow wire) and terminal 2 (black wire) on the sensor side of each connector. The resistance should be 860 to 1,060 ohms.

3 Also check the resistance between terminal 3 and either terminal 1 or terminal 2. The resistance should be approximately 100 000

ohms.

4 If the reading(s) are incorrect, renew the sensor(s).

Renewal

5 Remove the sensor mounting screw(s), using an Allen key where necessary, and pull the sensor(s) from the sockets. Disconnect

the wiring from one sensor at a time - be sure the connectors are not interchanged when fitting new sensors. The bellhousing is marked

with a B for the position sensor (grey connector) and D for the speed sensor (black connector) (see illustration). Note: It is a good idea to check the condition of the raised pin on the flywheel while the sensors are out of the sockets. Turn the engine by hand as necessary to bring the pin into view.

6 Tighten the sensor mounting screw(s) securely, but be careful not to overtighten.

 Pulse sensor (later models)

Check

7 Locate the two electrical connectors for the sensor (see illustrations). Disconnect the electrical connector from the front.

8 Using an ohmmeter, check resistance between terminal 1 (yellow wire) and terminal 2 (black wire) on the sensor side of each connector (see illustration). The resistance should be 500 to 600 ohms.

9 If the reading is incorrect, renew the sensor.

Renewal 

10 Remove the pulse sensor mounting bolt using a 5 mm hex spanner (see illustration). Withdraw the sensor from its bracket and

remove it.  

11 When fitting the new sensor, use a brass feeler gauge to position the tip of the sensor the correct distance from the pulse wheel (see illustration). 

12 Tighten the mounting bolt, but be careful not to overtighten it