Antilock Braking System (ABS)

DTC 35 Rear Wheel Speed Sensor Circuit Malfunction:

CIRCUIT DESCRIPTION
As the differential pinion gear turns, the speed sensor creates an AC voltage as the toothed ring (mounted to the differential pinion gear) rotates by the stationary sensor. The sensor consists of a permanent magnet and coil generating voltage by magnetic induction. The frequency and voltage of the induced signal is proportional to rear axle speed.
The EBCM uses the speed sensor signal to calculate vehicle reference speed, individual speed, acceleration and slip values for the rear wheels which determine when antilock control is required.

DTC 35 WILL SET WHEN
There is a short to voltage or ground in CKT 1811 or 1810, or a malfunctioning speed sensor. The testing for this malfunction occurs when the vehicle is in motion; it will not set with the ignition "ON" and the vehicle at rest.

ACTION TAKEN
If a malfunction is detected which causes a speed sensor DTC 35 to set, antilock braking is disabled and the EBCM turns "ON" the ABS warning lamp for the remainder of the ignition cycle. If the malfunction is intermittent, the EBCM will enable the system at the next ignition cycle and a history DTC 35 will be present.

IMPORTANT
^ The rear axle speed sensor is located in the rear axle housing. In order to prevent electromagnetic interference from disturbing the speed sensor signal, the sensor wires are twisted together 9 times for every foot of wire.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for a short to battery in either of the speed sensor circuit wires.
2. Checks for a short between the speed sensor circuit wires.
3. Checks for a short to ground in the speed sensor input circuit wire. The ground may be either a "hard" short to ground, or a resistive (partial) short. A short with a resistance less than 2 megohms, though not a "hard" short, can still cause DTC 35 to set.
4. Checks if the DTC resets during a road test. If so, since tests 1-4 have validated that all of the circuitry and components are good, intermittent malfunctions are suspected.
5. Checks wiring and connectors for intermittents.
6. Checks for sensor mounting, toothed wheel, and rear wheel bearing malfunctions which may be causing the malfunction. Check the toothed wheel for any large grooves, gouges, marks, etc. that might influence the tooth's signal at the wheel speed sensor. Also check for a buildup of foreign material in the gaps between teeth in the toothed wheel this material may cause this malfunction.
7. Replace the speed sensor assembly, as it is likely the cause of a DTC reset experienced during the road test, since other portions of the circuit have checked out OK.
8. Ensures DTC was not set due to electromagnetic interference.

DIAGNOSTIC AIDS
Setting of speed sensor DTCs may be caused by improperly mounted sensors or improper wire routing. Verify that the sensor is properly mounted and free of foreign material such as metallic particles, dirt or grease. If rear axle service was performed and the rear axle toothed wheel was removed it must be replaced. Verify that sensor wires are properly routed and secure. Improper rear axle wheel speed sensor wire routing may cause DTC 21 and/or DTC 25 to set. To aid in troubleshooting intermittent conditions the Tech 1 can be used while test driving the vehicle however, antilock braking will be disabled. Refer to the Tech 1 Brake Cartridge Operators Manual for additional information. If this does not identify the intermittent, wet the speed sensor harness on the underside of the vehicle and road test monitoring wheel speeds with the Tech 1.