Test Point 2

Test point 2
Front left speed sensor, signal implausible

DTC 4206

Control module receives a false / unrealistic speed sensor signal.

Procedure
Check the speed sensor signal with the System Tester 2 via the "Actual values" menu. To do this, call up the front left wheel speed.

Two tests are possible here.
Test 1 with raised vehicle.
(Swap of speed sensors and test of the speed sensor signal quality).

Test 2 with vehicle driving straight at approx. 2-4 km/h.
(Comparison of wheel speed signal qualities with each other).
Test 2 is a better measure of the signal quality than is test 1.

Further to test 1
To perform the test, manually rotate the left front wheel at a speed of approx. 2 - 3 km/h (observe display in the Tester screen).
Slowly increase the speed and simultaneously observe the speed increase (display).

Nominal values/required display
Speed steps of approx. 0.06 km/h. First display at 1.81 km/h.
This means: From the value measured last, the next value must be 0.06 km/h higher or, if the wheel is rotating slower, must be 0.06 km/h lower.
The Tester rounds the value down to 0.05 km/h or up to 0.07 km/h in some cases.
Example
First measured value = 1.81 km/h
Second nominal value = 1.87 km/h
Third nominal value = 1.93 km/h
etc.

Further to test 2
Display all four wheels in the Tester display.
Drive straight ahead at a uniform speed of approx. 2-4 km/h and have a second person observe the Tester display.
Required display: Deviation between the wheel speeds of the four wheels max. 1 km/h.
Further details about tests 1 and 2 are given under "Actual values menu" on P. 45 - D 38.

Possible faults (cause in the event of deviation)
- Air gap between speed sensor and gear wheel (pulse wheel) too large or, due to wear (chip formation), too small (check installation).
- Pulse wheel defective or corroded.
- Wheel bearing damage (wheel bearing not adjustable).
- Plug connection in wiring from the speed sensor to the control module or PIN on the control module connector not OK.