A Wash and a Wish Isn't Prep: Five Winter Checks That Keep Trade Margin Alive

Ask a trader what their PDI involves and you will often get the same answer: a wash, a hoover, a fresh set of plates and a bit of optimism. That is not a pre-delivery inspection. That is a valet with a clipboard attached.

In June, you can sometimes get away with it. In November, you cannot. Cold starts, salted roads, flat batteries and buyers who know how to use a code reader have a habit of turning a quick forecourt flip into a three-week headache. The margin you thought you had gets eaten by a recovery truck, a warranty argument and a Google review that starts with the words ‘bought a car from these lot’.

None of this is about turning your prep bay into a main dealer workshop. It is about five checks that take less time than a photoshoot and catch the stuff that actually costs you money.

1. Fluids: the cheap stuff that causes expensive comebacks

Start with coolant. Not a glance at the expansion bottle. A proper check of strength with a refractometer, because a car that has been topped up with water all summer will not thank you when the first hard frost arrives. A cracked head or a failed water pump is not a warranty conversation you want to have in December.

Then oil. Level and condition. If it is black and thin on a car you have just bought at auction, change it before it goes on the forecourt. It is a £40 job that makes the car feel looked after and gives you something to point at when a buyer asks what you have done.

Screenwash should be neat enough to survive -10°C, not a splash of blue water. Brake fluid should be clear and at the right level. These are small things, but they are the difference between a car that feels prepared and a car that feels like it has been wiped over with a damp cloth.

2. Brakes: standing stock and salt do not mix

A car can pass an MOT with brakes that are technically legal and still feel dreadful. If it has been sitting on a wet forecourt for three weeks, the discs will have a layer of surface rust and the pads may have stuck to the discs. A quick drive around the block might clean them up. A quick drive around the block might also hide a seized caliper.

Check pad thickness properly. Look at the inner pads, not just the outer ones you can see through the wheel. Check the handbrake operation. Check for corrosion on the brake pipes. And if the brake fluid has not been changed in living memory, factor it in. Brakes are the first thing a buyer tests on a test drive and the first thing they mention when they are unhappy.

3. Tyres: legal is not the same as sellable

We all know the legal limit is 1.6mm. We also know that a car with 1.8mm tyres on the front will be back on your forecourt in a month with a complaint, especially once the weather turns. For winter stock, 3mm is a more sensible line in the sand.

Check pressures when the tyres are cold. Check for sidewall damage, bulges and uneven wear that points to alignment issues. Check that the tyres match across an axle, or at least that they are a sensible brand pairing. A car on four mismatched budgets is a car that tells a buyer you were not paying attention. That is not the message you want before they have even asked for the keys.

4. Battery: the number that decides your January phone bill

A battery that starts fine in the mild November afternoon can be useless by the first proper frost. Use a proper battery tester, not a jump pack and a prayer. Check the cold cranking amps against the battery’s rated figure. Check the date code. Check the charging system while you are there.

Stop-start cars with AGM batteries are a particular trap. They are expensive, they do not like being left standing, and a weak one will throw all sorts of electrical gremlins that look like something much worse. A £90 battery is cheaper than a recovery call-out and a customer who has decided you sold them a pup.

5. Live data, not just fault codes

A basic code reader tells you if the engine light is on. It does not tell you why. A live-data scan tells you whether there are pending codes, whether the readiness monitors have been reset, whether the fuel trims are drifting, whether the glow plugs are working, whether the DPF is half-blocked or whether the misfire counter is quietly ticking up on one cylinder.

This is the check that separates a trader who is prepared from a trader who is hoping. It also gives you a baseline. If a fault appears two weeks after sale, you know whether it was there at prep or whether it developed later. That is worth real money when a warranty claim lands on your desk.

The paperwork is the margin

None of these checks mean much if you cannot prove you did them. A simple checklist per car, with the date, the technician’s initials and a photo of the battery tester result or the tyre tread gauge, is enough. It does not need to be a leather-bound file. A folder on your phone and a printed sheet in the car’s history is fine.

That paperwork does three things. It protects your warranty position, because you can show the car was inspected before sale. It protects your reputation, because you can answer a complaint with facts rather than shrugs. And it protects your margin, because you catch the £200 problem before it becomes the £2,000 comeback.

A valet makes a car look ready. A proper PDI makes it ready. In winter, the difference is the whole ballgame.