DTC 28 - Wheel Speed Sensor Frequency Error: Notes

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

DTC 28 will set if EBCM cannot specifically identify which wheel speed sensor is causing frequency error. If EBCM can identify specific wheel speed sensor causing trouble, DTC for that sensor (DTC 21, 25, or 35) will be set instead of DTC 28.

If DTC 28 is set, anti-lock braking is disabled and EBCM turns on ANTI-LOCK indicator for remainder of ignition cycle. If failure is intermittent, EBCM will enable system at next ignition cycle and a history DTC 28 will be present.

1. Checks wiring and connectors. Performing this step is critical as wiring or connector malfunction is most likely cause for this DTC to set.
2. Monitors electrical system for noise picked up by wheel speed sensor circuits.
3. Monitors wheel speed sensors while vehicle is operating. If Tech 1 auto-trigger snapshot mode triggers, wheel speed sensor or wiring and/or connectors are going intermittent during road test.
4. Checks resistance of wheel speed sensor.
5. Replaces wheel speed sensor as most likely cause of intermittent.
6. Ensures DTC does not reset due to faulty EBCM.
7. Checks for short to ground in speed sensor input circuit wires. A short with a resistance of less than 2 megohms, though not a direct short, may set DTC 28.
8. Ensures DTC is not due to electro-magnetic interference.