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Could the dealer have damaged my engine by washing it?

My Mazda went into the dealer for routine service and, when I drove it out, it was not driving properly; the transmission seemed like it was in trouble. The dealership said staff only washed the engine with a pressure hose and changed the drive belt. My car was amazing before this service, but now I can't prove that they caused damage. Can you guide me? – Jada S.

Fortunately, the transmission is well sealed making it unlikely than any water made its way inside. It is possible that some of the high-pressure water may have penetrated the vehicle's wiring harness or modules, causing an odd electrical issue. This is uncommon, however, with complications only becoming apparent after an extended period of time once corrosion has set in.

The most common side-effect of an engine shampoo is water collecting around the vehicle's ignition systems coils, wires and spark plugs. If these components get wet, poor drivability is immediately felt by the driver. The unwanted water provides an alternative electrical path, allowing the ignition coil's electrical charge to partially short out to the engine block instead of it reaching the spark plug. When this happens, the weaker spark only partially ignites the fuel, causing the engine to stumble or skip, also known as a "misfire".

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A slight engine misfire can feel like a transmission issue. You should insist that the dealer re-inspect the ignition system and dry out any moisture.

I only recommend engine shampoos when attempting to locate the source of an oil leak and need a clean starting point.

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing "Lou's Garage" in the subject area.

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