G1 brakes: drum, disc and assist service

Incorrect: On a single-wire grounding sensor an open wire can never complete the circuit, so it keeps the light off.

Incorrect: Low fluid lights the red brake warning lamp, not the pad wear indicator.

Correct: A single-wire sensor lights the lamp when worn pads let its contact ground against the rotor; with 6 mm left, a chafed wire touching ground does the same.

Incorrect: The only sensor is on the left front inner pad, so wear on the right front cannot trigger this light.

Incorrect: The instrument cluster only displays what the sensor circuit reports; condemning it before checking for a grounded wire skips the obvious cause.

Incorrect: The ABS module is not suspected; air in the lines is the expected cause after a caliper replacement.

Incorrect: Booster pushrod adjustment changes pedal height and free play, not sponginess.

Incorrect: A road test with a pedal that is still soft puts the vehicle on the road with a known defect.

Correct: Air can move past the one wheel that was bled; bleeding the full system in the specified sequence (with a scan tool on some ABS units) removes it.

Incorrect: The master cylinder was not touched in this job; a soft pedal right after opening the system points to air first.

Incorrect: The cooling vanes are inside the rotor; their shape does not create dark patches on the friction face.

Correct: Uneven pad material transfer leaves patches of different friction on the rotor; the pad grabs and slips as they pass, felt as vibration even though the rotor measures in spec.

Incorrect: A loose wheel bearing gives play and noise all the time, and it would not leave dark patches on the rotor face.

Incorrect: A hydraulic restriction causes drag or a pull, not vibration from patches on the rotor.

Incorrect: Lateral runout was measured within specification, so it is not the source here.

Incorrect: Vehicle B is at the replacement point now; another 3,000 miles would take it below the minimum.

Incorrect: Vehicle A's 4 mm is above the 3 mm minimum, so the specification does not require replacing those pads.

Correct: Vehicle B has reached the 3 mm minimum, so its pads are replaced; Vehicle A is above the minimum and can be noted for a recheck.

Incorrect: Vehicle B is already at the minimum; monitoring it lets the pads wear below specification.

Incorrect: Pad thickness says nothing about the fluid; a flush is decided by fluid testing.

Correct: With an ABS fault the anti-lock function shuts off, but the base hydraulic brakes and power assist keep working normally.

Incorrect: A wheel speed sensor fault does not command the parking brake.

Incorrect: Power assist comes from the booster, which a wheel speed sensor fault does not disable.

Incorrect: A failed sensor does not apply or release one brake, so the vehicle has no pull in normal stops.

Incorrect: The base hydraulic brakes do not depend on the ABS sensor, so the service brakes still work.

Incorrect: Lining wear lowers the reservoir slightly as pistons move out, but it never leaves the backing plate damp.

Incorrect: A seeping reservoir seal wets the master cylinder on the firewall, not a rear backing plate.

Incorrect: The metering valve sits in the front brake circuit near the master cylinder; it cannot wet a rear backing plate.

Incorrect: A brake drum is not part of the hydraulic system, so porosity in it cannot leak fluid.

Correct: Worn wheel cylinder cups seep fluid that runs down the backing plate under the cylinder while the reservoir level drops.

Correct: The wear sensor should have triggered the warning long before the pad reached the backing plate; its circuit or contact has failed.

Incorrect: A pad worn to metal is exactly what the sensor exists to report, so no warning is not normal operation.

Incorrect: A glazed pad surface affects friction, not whether the sensor reports a worn-out pad.

Incorrect: The ABS hydraulic unit has no role in pad wear sensing.

Incorrect: A low brake fluid level would turn a warning on, not keep the pad wear light off.

Incorrect: 1 mm is the difference between the two numbers, which means nothing for pad wear.

Incorrect: 5 mm is the steel backing plate, not the friction material.

Incorrect: 9 mm adds the 5 mm backing plate, which never wears and is not lining.

Incorrect: 4.5 mm averages the lining and the backing plate, which measures neither.

Correct: Pad thickness for inspection is the friction material only, so 4 mm is recorded.

Incorrect: A stuck ABS valve would hold hydraulic pressure, and the free-moving piston shows there is none.

Correct: The piston moves freely, so hydraulics are not holding the brake; a seized parking brake cable keeps the rear brake applied mechanically.

Incorrect: A blocked master cylinder port would make more than one wheel drag and would hold pressure against the piston.

Incorrect: The piston compresses easily with a C-clamp, so the caliper piston is not frozen.

Incorrect: A restricted hose traps hydraulic pressure, but the piston pushes back freely, so no pressure is held.

Incorrect: Fluid color darkens with age and contamination, but it does not tell how much water the fluid holds.

Incorrect: Copper level shows corrosion inhibitor depletion, not moisture saturation.

Incorrect: A galvanic voltage reading points to corrosion activity, not to the water content of the fluid.

Correct: Absorbed water lowers the fluid's boiling point, so a boiling point test measures the effect of moisture directly.

Incorrect: The reservoir fluid level reflects pad wear or leaks; it says nothing about water in the fluid.

Incorrect: A seized front caliper piston causes a pull or drag, not high pedal effort on every stop.

Incorrect: No external leaks were found, and a leaking wheel cylinder would make the pedal low, not hard.

Incorrect: An internal master cylinder leak lets the pedal sink; it does not make it hard.

Correct: Without vacuum the booster gives no assist, so the pedal is hard and needs a lot of force; a failed check valve or hose cuts that vacuum.

Incorrect: Air in the brake lines makes the pedal soft and spongy, the opposite of hard.