mm28 Anti Lock Braking Systems ABS for Trucks, Tractors, and Buses C Version

3 Troubleshooting

VOM Setting (Test Adaptor Pins)

Speed Sensor Resistance Test or Measurement

Vehicle Ignition

(Record) Actual Measurement

Desired Measurement

Possible Causes of Malfunction

Other Action

Ohms LF 15 & 32 RF 17 & 34 LR 18 & 35 RR 16 & 33

OFF

700-3000 ohms

Broken wire between ECU and sensor Sensor connector Defective sensor Shorted sensor wire Chafed/cut sensor cable Defective sensor

Ohms LF 15 & 27 RF 17 & 27 LR 18 & 27 RR 16 & 27 Volts AC LF 15 & 32 RF 17 & 34 LR 18 & 35 RR 16 & 33

Speed Sensor Resistance to Ground

OFF

> 30K ohms

Speed Sensor Adjustment

OFF

> 0.200 VAC

Turn wheel by hand at 30 RPM (2 sec./ rev.)

No reading

— Sensor wire broken — Sensor wire shorted

Sensor gap too large Large variation

— Excessive tone ring runout — Tone ring damaged — Excessive wheel bearing end play

WABCO Maintenance Manual MM-28 (Revised 03.2020)

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