Front Speed Sensor
Removing and Installing Front Speed Sensor
Removal
1. With the ignition switched off, open the combination plug connection at the spring strut and pull out the plug for the speed sensor.
2. Loosen the fastening screw (hexagon socket head bolt) and remove the speed sensor.
Important notes
Before installation, ensure that there are no metal chips at the magnetic edge of the speed sensor.
The gap between speed sensor and pulse wheel is determined by the design and cannot be adjusted.
Installation
1. Coat speed sensor and the bore in the wheel carrier with Molykote Longterm.
Important: There is no O-ring between the speed sensor and the wheel carrier.
Furthermore, ensure that the speed sensors for the front axle are not interchanged with those for the rear axle, otherwise the edge position of the speed sensor will be offset by 90° with respect to the pulse edge.*
Distinguishing characteristic:
Identification on the speed sensor lead by means of added spare part No. and position of the fastening bore with respect to the edge position.
1 = Speed sensor, front axle*
2 = Speed sensor, rear axle*
* The statement that the speed sensors for the front axle/rear axle must not be interchanged no longer applies to speed sensors installed after 24.11.1995. See New Speed Sensor in this article for information on this.
2. Without using excessive force, insert speed sensor into wheel carrier without applying any force and tighten the hexagon head bolt to 10 Nm (7.5 ftlb).
3. If the speed sensor has been removed or replaced due to an ABS fault or ABS / ABD fault, or because of accident repairs, a functional check should be carried out with the System Tester 9288 - via the Actual Values menu, Speed submenu. Refer to Antilock Brake System, Testing and Inspection.
New Speed Sensor
The speed sensors for the front and rear axles have been standardized. As of 24.11.1995, the same speed sensor, part No. 993 606 405 00, has been installed on all four wheels of new vehicles.
Repairs:
The previous speed sensors - part No. 993.606.404.00 for the front axle and 993.606.402.00 for the rear axle - are no longer available.
In case of spare parts requirements, the new speed sensor (part No. 993.606.405.00) is also valid for vehicles manufactured prior to the aforementioned introduction date.
Important: a mixed configuration on an axle is NOT permissible. In other words, if a previous-model speed sensor, part No. 993.606.404.00 or 993.606.402.00, is replaced with a new speed sensor (part No. 993.606.405.00), both sensors on the axle in question must be replaced!
A mixed compliment with different speed sensors mounted on the front axle than on the rear axle is permissible.
If the previous version is installed together with the new version on the same axle, the different reception sensitivity values can cause the ABS warning light to light up and thereby can deactivate the ABS function.
DISTINGUISHING CHARACTERISTIC:
Part No. printed on the speed sensor lead.
The statement that the speed sensor for the front axle must not be interchanged with the speed sensor for the rear axle, as otherwise the edge position of the speed sensor will be offset by 90° with respect to the pulse edge no longer applies to the new speed sensor.