DTC 28

DTC 28 Wheel Speed sensor Circuit Frequency Malfunction






DTC will set when:

1. One wheel is detected at least 19 mph (30 kph) faster than the remaining wheels for an extended period of time.
2. One wheel is at least 6 kph (4 mph) less than or greater than the remaining wheels for an extended period of time.

Code 28 is set if the EBTCM cannot specifically identify which wheel speed sensor is causing the frequency error problem.

Action Taken

1. Code set.
2. ABS/TCS switched "OFF".
3. "ANTILOCK" indicator "ON".
4. "TRACTION DISABLED" message displayed.

Test Description

Test numbers refer to circled numbers on the diagnostic chart.

1. Checks wiring and connections for problems. It is critical that this step is performed thoroughly, as wiring/connector problems are the most likely cause for this code.
2. Use the TECH 1 to check for sources of induced electrical noise.
3. Checks for damaged wheel speed sensor and/or loose circuit connections.
4. Checks for proper sensor resistance.
5. a) Replaces front wheel speed sensor as the likely cause of the triggering intermittent. b) Replaces rear wheel speed sensor as the likely cause of the triggering intermittent
6. Checks if the Code resets after wheel speed sensor replacement.
7. Checks for a short to ground in the speed sensor input circuit wires. The circuit to be tested depends on which speed sensor triggered the TECH 1. The ground may be either a "hard" short to ground, or a resistive short. A short with a resistance less that 2 M ohms, though not a hard short, can still cause Code 28 to set.

Diagnostic Aids

Be sure the speed sensor wiring is properly routed and retained. This will help prevent false signals due to electrical noise being picked up by the wiring. It is very important that a thorough inspection of the wiring and connectors be performed. Another condition that may set DTC 28 is if more than one sensor signal has a problem.

A worn hub/bearing assembly may cause this fault, in extreme cases the bearing play allows the sensor to toothed-ring gap to change excessively. Never reuse a wheel speed sensor once it has been separated from the front hub/bearing assembly.