CASE 009
ABS Warning and Intermittent Pulses
advanced
22 min
Petrol
Vehicle
- ModelTraining Hatch 1.2
- Engine1.2 16V
- Mileage88,000 km
Customer complaint
The ABS light comes on intermittently at low speed and the pedal pulses occasionally when braking gently.
History
Wheel bearing replaced on the front right 2,000 km ago.
Fault codes
C0035 Left front wheel speed sensor circuitC0040 Right front wheel speed sensor circuit (intermittent)
Live data
- Wheel speeds at walking paceOne wheel briefly drops to zero
Measurements
- Sensor resistanceSimilar on both front sensors
- Scope waveform, right frontSignal drops out over bumps
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Diagnostic case
Next step — Reasoning.
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Confirmed cause
Intermittent signal loss at the right front wheel speed sensor, consistent with a loose sensor, air gap or damaged reluctor after the recent bearing work.
Reasoning
Intermittent dropouts that appear over bumps and after bearing work suggest a mechanical/air-gap or harness issue rather than a failed sensor. Static resistance tests can pass while the signal still drops out dynamically, which is why a scope recording and wiggle test are decisive.
Recommended repair
- Inspect the sensor mounting, air gap and reluctor ring.
- Check the harness and connector for damage.
- Repair, clear codes and confirm stable wheel speeds on a road test with live data.
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.