Test Point 3 - Speed Transmitter
TEST POINT 3 - DME 944Speed Sensor
The speed sensor can only be tested with an oscilloscope.
A workshop oscilloscope will be required to have correct oscillographs. Adjust oscilloscope to supplier's instructions.
Connect control unit plug terminals 8 and 27 on oscilloscope tester via test leads.
Start engine: screen must display sine oscillation, of which the amplitude must be > 2.5 V!
If voltage signal is too small (< 2.5 V), distance between sensor and gear ring is excessive or speed sensor is defective.
Distance between gear ring and sensor: 0.8 ± 0.3 mm.
No Display:
Disconnect speed sensor plug on plug plate in engine compartment. Connect oscilloscope tester leads on plug with help of test leads.
Connect test leads on center and outer plug pins of plug (term. 1 and 2).
Start engine. Sine oscillation must be visible on screen.
Check sensor for power flow, spacing and dirt, replacing sensor if necessary.
Sensor adjustment: see Engine Speed Sensor. Adjustments