Why Your Check Engine Light Comes On After a Car Wash

If your dashboard’s check engine light illuminates after a car wash, it might or might not signal a serious issue. Moisture could have triggered the light, potentially seeping into the engine and harming critical components like wires or pipes, leading to costly repairs.

Why Does the Check Engine Light Come On After a Car Wash?

Moisture is a frequent adversary for vehicles. Since the dawn of automobiles, manufacturers have worked to shield cars from water damage.

However, the equipment used to clean our cars can sometimes cause harm instead.

Below are typical problems that may arise after a car wash.

Damaged Sensors Near the Engine

Water can infiltrate the engine compartment or battery area in several ways. If a vehicle is partially submerged, water may enter from the sides or beneath, affecting the battery.

Even the hood might not fully shield the engine from water, particularly from high-pressure sprays at car washes. Once water enters the engine area, it can combine with dirt and debris already present.

This mixture can form a sludge that damages the engine or battery. Sensors, crucial for the vehicle’s monitoring system, may malfunction if exposed to water and grime, triggering the check engine light.

A faulty sensor disrupts the vehicle’s computer system, as it fails to relay accurate data, causing the check engine light to activate.

Improper Sealing by the Manufacturer

Manufacturing defects are not uncommon in the automotive world. Issues like faulty navigation, defective software, or brake problems have been reported by brands like Ford, Lexus, and Mercedes-Benz in recent years.

It’s possible that your vehicle’s manufacturer failed to adequately seal it against water intrusion. Alternatively, a defective unit might have slipped through quality control unnoticed.

Older vehicles, in particular, may have more gaps, allowing water to enter and interfere with internal systems.

Water in the Air Intake

Vehicles with air intake systems positioned lower on the body are more prone to water-related issues.

Mass air flow sensors, often located near fuel injectors, regulate air entering the engine’s cylinders. These sensors ensure the right amount of fuel is delivered.

A small amount of water in the air intake may evaporate due to engine heat. However, if significant water accumulates, you’ll need a mechanic to clear it out, along with any mold or debris in the system.

Failing Catalytic Converter

One of the most severe issues post-car wash is a malfunctioning catalytic converter. This component reduces harmful emissions produced by the engine.

A faulty catalytic converter can prevent your vehicle from passing a smog test, rendering it illegal to drive, even with valid registration and insurance.

When the catalytic converter fails, the check engine light and other warning indicators may light up.

Signs of a failing catalytic converter include reduced fuel efficiency, frequent engine misfires, or a rattling sound from the engine. Replacing this part is costly, with prices ranging from $800 to $1,200, excluding labor charges.

What to Do When the Check Engine Light Comes On

Don’t ignore a check engine light and continue driving. Neglecting it can worsen the problem. Book a maintenance appointment with your mechanic, who can use diagnostic tools to pinpoint the cause. Mention your recent car wash visit so they can check for water-related damage.

Check Engine Light Persists After Inspection

If the check engine light keeps reappearing after a mechanic’s inspection, the issue might lie with the light’s wiring. Moisture or physical jolts can damage dashboard wiring. Ask your mechanic to inspect the dashboard’s lighting system for a blown fuse or faulty wiring.

Final Thoughts

Post-car wash issues, such as water entering the air intake, can trigger the check engine light. The most effective way to diagnose the problem is by using diagnostic codes. A mechanic can interpret these codes to identify malfunctioning components in your vehicle.