DTC 28 - Wheel Speed Sensor Frequency Error: Notes

Toothed wheel generates a voltage pulse as it moves past wheel speed sensor. EBTCM uses the frequency of these pulses to determine wheel speed. Amount of voltage generated in each pulse depends on wheel speed and on air gap between wheel speed sensor and toothed wheel.

SERVICE ABS and SERVICE ASR indicators will be on and DTC 28 will be set if EBTCM cannot specifically identify which wheel speed sensor is causing the frequency error problem. If EBTCM can identify which speed sensor is causing the problem, the DTC associated with that sensor (DTC 21, 25, 31 or 35) will be set instead of DTC 28.

1. Checks for problems in wiring and connections. Wiring and connector problems are the most likely cause for this DTC being set.
2. Uses Tech 1 scan tester to monitor for vehicle electrical/electronic system noise being picked up by the speed sensor circuits.
3. Uses Tech 1 scan tester to monitor speed sensors while vehicle is moving. If Tech 1 Auto-Trigger Snapshot mode triggers during road test, an intermittent fault exists in speed sensor, wiring and/or connectors.
4. Checks for correct resistance reading of wheel speed sensor. 5a) Rear wheel speed sensor is most likely cause of intermittent. 5b) Front wheel bearing/speed sensor is most likely cause of intermittent.
5. Uses Tech 1 scan tester to monitor speed sensors while vehicle is moving. If Tech 1 Auto-Trigger Snapshot mode triggers during road test, EBTCM is detecting a non-existent problem with wheel speed sensor frequencies.
6. Checks for a short to ground in speed sensor input circuit wires. Test circuit that triggered Tech 1 scan tester in step 2). Ground may be a hard, constant short to ground or a partial (resistive) short. A resistive short of less than 2 megohms can set a DTC 28 if EBTCM cannot identify the faulty speed sensor circuit.