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2002 Toyota Sienna CEL P0401

The CEL in my mother’s 2002 Sienna is on. It is a solid light, not blinking. I sent her to Pep Boys to get the codes read. She came back with P0401. The guy at Pep Boys says the problem is “EGR Insufficient Flow Detected.”

I placed my hand near the exhaust pipe and it doesn’t feel like it is flowing like it should. The normal puffs of exhaust aren’t there. The exhaust gas comes out constantly instead.

Since the owner’s manual recommends high octane fuel for better performance, but it doesn’t require it, she has been using regular 87 octane gas to save money. She made this decision based on what is written in the owner’s manual, so I am hoping it didn’t cause the problem.

What does this code mean? Is it time for new catalytic converters? Is it time to go back to expensive gas?

One thing to check for this code is the EGR vacuum control solenoid. This solenoid is commanded by the computer when and when not to supply engine vacuum to the EGR valve. If this solenoid has failed and doesn’t allow engine vacuum to the EGR valve it’ll trigger this code.


Thanks, Tester. That is where I will start.

The EGR system is tapped off the exhaust way up on the engine, either on the exhaust manifold or inside the cylinder head. By using lower octane fuel, the EGR passages may be clogged with soot and carbon. This would restrict gas flow through the EGR system, and set this code. If the vacuum lines are good and the EGR valve is functioning properly, then the lines may need to be cleaned out. Switching gas now will not help.