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Toyota RAV4 1999 - P0401 and P1133 Fault Codes: Diagnosis and Solutions

Model: Toyota RAV4 Fault Code: P0401 Posted: 2007-10-12 14:02

My 1999 Toyota RAV4 has the check engine light on, with fault codes P0401 and P1135. I understand that P1133 refers to the oxygen sensor (O2) for Bank 1 Sensor 1, but my Haynes manual only lists Bank 1 Sensor 2 and Bank 2 Sensor 2. Where is Bank 1 Sensor 1 located? Can someone provide a diagram or photo? Regarding P0401 — 'EGR Insufficient Flow Detected' — what should I check first? What are the most common causes of this code? How do I diagnose it step-by-step? I'm looking for clear, accurate guidance to avoid buying incorrect parts. Any help would be greatly appreciated.

Related fault codes
P0401P1133
Comments (4)
Anonymous 2007-10-12 15:57

P1133 refers to the upstream oxygen sensor on Bank 1. The '1/1' indicates Bank 1, Sensor 1 (upstream). Most vehicles have two O2 sensors per bank — one upstream and one downstream. Confirm how many total O2 sensors are in your system to ensure you're referencing the correct one.

Anonymous 2007-10-14 16:54

The most likely cause of P0401 is a clogged or malfunctioning EGR valve. Start by inspecting the EGR valve for carbon buildup and ensuring it opens properly. Clean the valve with appropriate cleaner, then test its operation. If that doesn't resolve the issue, use an oscilloscope to check the signal from Bank 1 and Bank 2 Sensor 1 (upstream O2 sensors) for proper response.

Anonymous 2007-10-15 08:25

I'm confused too — is 'air flow' referring to MAF or air/fuel ratio? Clarifying terminology here helps avoid misdiagnosis. The correct term in this context is the oxygen sensor (O2), not air/fuel sensors.

Anonymous 2007-10-15 08:57

I've seen too many online forum posts where users buy wrong parts because they rely on generic advice. For example, confusing 'MAF' with 'O2 sensors'. It's frustrating when people end up with incorrect replacements and complain about poor performance. This kind of misinformation can really hurt DIYers — it's a good reminder to verify part numbers and use proper diagnostic tools.