The pre-departure check with an ABS warning
On a January morning you are due to take 15 passengers in your D1 minibus with a 1,500 kg trailer. The pre-departure check shows: front tyres 2.2 bar against 3.0 bar recommended; a rear minibus tyre at 1.8 mm tread; both trailer tyres at 1.2 mm; the ABS warning lamp stays on after the self-test; the trailer's left brake light is dead; the brake fluid was last changed four years ago; and 10 cm of snow sits on the minibus roof. The outside temperature is −3 °C and the route includes a long downhill section. The vehicle otherwise starts and drives. You have a spare bulb and a foot pump, but no replacement trailer tyre.
1. Sort the findings into legal prohibitions, safety-critical defects and maintenance items. Can you depart?
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Legal prohibitions: the trailer tyres at 1.2 mm are below the 1.6 mm minimum for this trailer, and the dead trailer brake light means the lighting system is not compliant. Safety-critical defects: the ABS warning lamp staying on means the anti-lock system has a fault; the underinflated front tyres reduce steering grip and increase heat; the snow on the roof can slide onto the windscreen or into following traffic. Maintenance items: the brake fluid is four years old and should be tested or changed according to the service schedule, and the rear minibus tyre at 1.8 mm is legal but close to the limit. You cannot depart as loaded. The trailer tyre must be replaced, the brake light repaired, the ABS fault diagnosed, the front tyres inflated to 3.0 bar and the snow cleared before the passengers board.
2. What are the risks of driving with the ABS lamp on and underinflated front tyres on a downhill winter route?
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With the ABS lamp on, the system may be disabled. On a slippery downhill section the wheels can lock under braking, so you lose steering control and the stopping distance increases. The minibus is heavy and towing 1,500 kg, so the extra mass makes lock-up more likely. Underinflated front tyres reduce the contact patch and steering precision, generate more heat and rolling resistance, and can worsen understeer on a cold, damp surface. Combined with a long descent, the brakes and tyres will heat up more than normal. The correct response is not to drive more slowly and hope; the ABS fault and tyre pressures must be corrected first, and the downhill route should be driven with engine braking and a large gap.
3. What would you do before departure and what would you tell the passengers?
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Replace the trailer tyre or fit the spare if it is legal and correctly inflated; repair the brake light with the spare bulb and test all lights with a second person. Inflate the front tyres to 3.0 bar when cold, clear all snow from the roof, and check the trailer coupling, safety cable and brake linkage. Have the ABS fault checked; if it cannot be cleared, do not take passengers. Check the brake fluid condition and test the brakes at low speed in a safe area. Tell the passengers that the departure is delayed for a safety defect, not for a minor comfort issue, and that you will not drive until the trailer tyre, lights and ABS are sorted. If the delay is long, arrange a replacement vehicle rather than pressing the faulty combination into service.