Model 124

Only models 124.034 (400 E) and 124.036 (500 E) are equipped with electronic speedometers. The Service Microfiche does not yet include testing procedures. Use the following test procedure:


1. Remove instrument cluster.

2. Unplug connector for electronic speedometer.

3. Test the speed sensor with an ohmmeter (at the harness connector): Measure the resistance between socket 3 (sensor) and socket 4 (ground) of connector 5. Nominal value is 1.8 - 2.2 k ohms.

4. Test the electrical output of the speed sensor with the multimeter set to AC volts. Use the same connections as in Step 3 above. On vehicles with ASR, activate the snow chain switch (S76). With the rear wheels lifted and rotating, the output of the speed sensor must be > 0.2 V AC at approx. 10 mph (16 kph). Using the signal generator/frequency counter, check that the speed sensor output frequency increases in direct proportion to rear wheel speed.

5. Check the speedometer power supply at the harness connector with the multimeter set to DC volts. Measure the voltage between socket 2 (circuit 15) and socket 4 (ground) on the harness connector, with the ignition switch in position 2. Nominal value is battery voltage.

6. Using the electrical connector kit, connect power to the speedometer: pin 2 to power (12 V), pin 4 to ground. Set the signal generator to produce a sine wave > 1 V AC. Connect the signal generator to the speedometer: red wire from signal generator to pin 3, black wire from signal generator to pin 1 (ground).

7. Confirm the vehicle model tested.





Set the signal generator frequency output according to Table 1.

Test the speedometer at all 3 frequencies listed. The speed indicated must fall within the tolerance range shown.

Note:
Perform this test as quickly as possible, since miles are being added to the odometer.

8. Reconnect and reinstall the instrument cluster, and verify proper operation of all instruments. Check and clear all DTCs that may have been set during testing.