Car washing and electronics: what pressure water damages

A car is designed for rain, and that is true. But rain does not fire a pressure jet into a connector from ten centimetres — a pressure washer does exactly that.

What does not tolerate pressure

Parking sensors. Water enters through the membrane and the system beeps with nothing there. It dries out in anything from hours to a day; covered in the parking sensors article.

Cameras. The housing seal is not designed for a direct jet; the result is permanent internal misting.

Engine bay connectors — especially on exposed sensors.

The mass airflow sensor and the intake area — water there gets expensive.

The alternator — it does not need a direct jet.

Radiator and condenser — pressure bends the fins, after which they shed heat worse. Wash along the fins and from a distance.

Decals, mouldings, and seals — pressure lifts them.

Headlights — hot after a drive while the water is cold; plus pressure drives moisture past the seals; covered in the headlight condensation article.

Washing the engine

The topic with the highest risk and the lowest necessity.

Why people do it: to find leaks, or before a sale.

What they risk: water in connectors producing intermittent codes in systems nobody touched; mechanics in the ghost codes article.

If you do wash it:

• With the engine cold — a hot head and cold water do not mix.
• No direct jet at connectors, alternator, fuse box, or sensors.
• Cover sensitive components with plastic.
• Dry with compressed air afterwards.
• Read the codes after the wash — mandatory.

The most common outcome: after an engine wash the car will not start or runs rough. That is water in the plug wells or the coil connectors.

In winter

Locks and seals — water freezes in them; covered in the freezing article.

Brakes — drive afterwards and dry them with light applications.

The handbrake — do not apply it onto frozen shoes.

Drains — clear them, or water stays in the sills; covered in the road salt article.

What to do after a wash

1. Dry the locks — blow them out or cycle them a few times.
2. Dry the brakes — a few light applications on the move.
3. Read the codes if the engine bay was washed.
4. Check the parking sensors — beeping usually clears within a day.
5. Do not leave a wet car on the handbrake in frost.

In short

• Rain does not fire a jet into a connector from ten centimetres; a washer does.
• Parking sensors and cameras are the main victims of close-range pressure.
• Wash the radiator along the fins and from a distance, or pressure bends them.
• After washing the engine bay, reading codes is mandatory.
• In winter, dry locks and brakes and do not apply the handbrake.

Download the app — codes across every system after a wash are read with an ELM327 adapter over Bluetooth SPP on Android.