Alphard ECU Error

Reduced power and an ECU error? Sounds like it could be a few things, but the ECU itself is a prime suspect. Could be a faulty sensor feeding it bad data, or the ECU itself might be on the fritz. Have you checked the main relay that supplies power to the ECU? A defective relay can cause intermittent issues and throw those kinds of errors. Easy and cheap to test/replace before diving deeper.

A faulty relay makes sense, actually. Where exactly is the main relay located, and how can I test it to see if it's the culprit before I start thinking about replacing the whole ECU?

The main relay's location can vary, but it's often in the engine bay's fuse box, sometimes under the dash. Check your owner's manual for its exact location and diagram. Testing involves checking for voltage at the relay and verifying it clicks when energized. If unsure, a workshop can pinpoint it quickly. Given the ECU error, it's best to have it professionally diagnosed.

Thanks so much! I followed your advice and had a workshop take a look. Turns out the main relay was defective! They replaced it, cleared the error codes, and the Alphard is running perfectly again. Total cost was only 120€. I really appreciate your help pointing me in the right direction!