Test Point 2

TEST POINT 2
Front Left Speed Sensor, Signal Implausible

DTC 4206

Fault effect: 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.

1. Test 1 with raised vehicle. (Swap of speed sensors and test of the speed sensor signal quality).

2. 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.

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 1.81km/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.

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". Actual Values (Actual Value Test)

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.