Brake Fade on a Long Descent with a Tyre Warning Already Lit

Diagnosis: brake fade, from heat, on a loaded vehicle on a sustained gradient.

The evidence, and what each item means:

• Soft, long pedal - the brake fluid is boiling. Vapour compresses, so pedal travel goes into squeezing gas instead of pushing pads. This is a fluid problem, not a pad problem.
• Speed creeping to 75 km/h under firm pressure - the pads are also past their working temperature and their friction coefficient has fallen away ('green fade').
• Acrid smell - resin and friction material cooking. By the time you can smell it, the system is well beyond its design temperature.

Why pressing harder is the wrong response: both failure modes worsen with heat, and harder, longer braking adds heat faster than it removes it. There is no pedal pressure that restores friction to a boiled system. Continuing to brake hard on this descent converts a warning into a total loss of brakes with 5 km still to run.

Why this descent in particular: a 7% grade over 8 km in a loaded SUV means the brakes are being asked to dissipate the potential energy of the whole descent, continuously, in 38 °C air. Engine braking was designed for exactly this and was not being used in D.

Next 200 metres - stop adding heat:

1. Select a low gear now. In a 7% descent, 2nd or manual mode second gear will hold the vehicle near 50–60 km/h on engine braking alone. This is the primary brake, and it works whether or not the brakes are hot.
2. Get off the brake pedal entirely for a few seconds at a time to let airflow cool the discs. Alternating short firm applications with cooling gaps beats riding the pedal continuously.
3. Hazard lights on to tell following traffic you are slow and unpredictable, and to discourage overtaking.
4. Look for a pull-off, lay-by or escape lane and plan to use the first safe one. Do not try to complete the descent on a known-failing system.

Next ten minutes - cool it properly:

• Stop on level ground off the carriageway, in gear or with the parking brake applied and wheels chocked.
• Let it cool naturally. Do not pour water on hot discs - the thermal shock can crack a disc or warp a hub. Do not touch the discs.
• Do not use the parking brake as a substitute while moving at speed. On many of these vehicles it acts on the rear wheels only and can lock them, spinning the car.
• Check the brake fluid level; a boiled system may have pushed fluid out. If the pedal is still long after cooling, the vehicle should not continue - a soft pedal after a full cool-down means air or fluid loss, and it needs recovery, not a top-up.
• Only continue once the pedal is firm and high, and continue in a low gear the whole way down, not just until the next corner.

A steady light is not an emergency, but in this context it moves the risk up a level.

What a steady light means: at least one tyre is outside its expected pressure range, most often low. A flashing light on some systems indicates a sensor fault; steady means a real pressure reading out of range.

Why it matters here specifically:

• Underinflation plus heat plus load is the classic blowout recipe. A soft tyre flexes more, generates more internal heat, and on a 38 °C day on an 8 km descent the margin is already thin.
• A rear tyre was topped up two days ago - which means it was losing pressure. It may still be losing it. A top-up is not a repair.
• A rear blowout while descending a mountain road is one of the hardest situations to recover from, particularly with a loaded vehicle and compromised brakes.

Decision: the tyre light is not the reason to stop - the brake fade already is - but it removes any argument for pressing on to the bottom. Stop at the pull-off, check all four pressures cold with a gauge, look for a nail or a damaged valve on the tyre that was topped up, and do not simply reset the warning and carry on. If the vehicle was driven on a soft tyre for two days at highway speed, have the tyre inspected for internal damage before continuing.