Spongy Brake Pedal and One Hot Wheel After Pad Fitting
After a front brake pad replacement on a 2016 hatchback, the technician tops up the brake fluid and road-tests the car. The pedal now travels about 55 mm before it feels firm, compared with 25 mm before the repair. The ABS warning lamp comes on during the road test. After ten stops from 50 km/h, the left front wheel hub measures 88 °C while the right front, left rear and right rear measure 42 °C, 40 °C and 41 °C. The fluid is dark and the service record shows it is three years old. The caliper slide pins were dry during pad fitting, and the bleed sequence used was left front first, then right front, left rear, right rear. The car pulls slightly to the left under braking.
1. Separate the causes of the spongy pedal and the hot left-front wheel. What would you check first?
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The spongy pedal points to air in the hydraulic system or deteriorated fluid, not to the pad friction material itself. The hot left-front wheel points to brake drag: a sticking caliper piston, dry or seized slide pins, or a collapsed flexible hose. The pull to the left fits a left brake that is applying more strongly or not releasing. Check the left-front caliper first: slide pins, piston retraction and pad freedom. Then inspect the hose for internal collapse. Do not replace the master cylinder yet; the evidence is localised to one wheel plus air in the system. The dark three-year-old fluid supports a full flush after the mechanical fault is corrected.
2. Explain why the ABS lamp may have illuminated and why simply clearing the code is unsafe.
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The ABS lamp may have come on because air or low fluid affected the hydraulic unit, because a wheel-speed sensor or its wiring was disturbed during the repair, or because the test drive exposed a wheel-speed signal problem. Clearing the code without repairing the cause can leave the ABS inactive. The lamp is a warning that the system may not modulate during an emergency stop. Scan for the specific code, inspect the sensor and reluctor ring at the left front, and check fluid level and bleed status. Clear the code only after the fault is repaired and the lamp stays off through a road test.
3. State the correct bleeding sequence and the fluid-handling steps for this car.
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The sequence used was wrong because the left front was bled first. A typical sequence starts at the wheel farthest from the master cylinder and works closer: right rear, left rear, right front, left front. Follow the manufacturer's sequence if it differs. Keep the reservoir above the minimum mark during bleeding, use fresh DOT 4 fluid from a sealed container, and do not reuse fluid bled out. Attach a clear hose to the bleeder and watch for air bubbles. If the ABS unit may contain air, use a scan tool to run the ABS bleed procedure. Finally, check pedal firmness and test the brakes at low speed before road testing.