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P0135 and P0300/P0301 Codes on 1998 Toyota Avalon: O2 Sensor Location and Misfire Diagnosis

Model: Toyota Avalon Fault Code: P0135 Posted: 2007-08-01 23:42

I'm experiencing trouble codes P0135, P0300, P0301 on my 1998 Toyota Avalon with over 198,000 miles. The traction control warning light is also illuminated. I recently installed new Bosch spark plugs six months ago—no wire replacement was done—and am unsure whether the oxygen sensor in question is located upstream or downstream on the front of the engine block. Based on this, I suspect a faulty O2 sensor may be causing an incorrect air-fuel ratio and resulting in misfires. Can anyone confirm the correct location of the upstream O2 sensor for bank 1 on a 1998 Avalon? Is it possible that a failing O2 sensor is triggering these codes?

Related fault codes
P0135
Comments (5)
Anonymous 2007-08-02 07:37

The oxygen sensor should be located at the front of the engine, specifically upstream on bank 1. In a two-sensor setup, this would be the sensor before the catalytic converter; in a three-sensor configuration common on V6 engines, it's the first O2 sensor for bank 1 upstream.

Anonymous 2007-08-03 05:17

I replaced the O2 sensor and noticed that the P0135 code disappeared. I also used my scanner to confirm misfires in cylinders #1 and #4. After swapping coils between #3 and #6, the misfire codes moved with them—this confirmed a faulty coil pack. I’ve ordered a new coil set as a next step. Thanks for the helpful insight.

Anonymous 2007-08-03 06:55

After the sensor replacement, the code shifted to P0XXX—suggesting that the original issue may have been resolved or redirected by the fix.

Anonymous 2007-10-07 15:31

I recommend using iridium spark plugs instead of Bosch platinum or standard types. I personally experienced persistent misfire codes and actual engine misfires when using Bosch 2-pronged plugs on my Toyota—switching to iridium resolved the issue completely.

Anonymous 2007-10-07 17:16

I disagree with the plug recommendation for Toyotas. While some vehicles, especially Isuzus, may have sensitivity issues with aftermarket plugs, I’ve never encountered such problems on any Toyota model. If a plug-related issue occurred in your case, it would be helpful to know specific details—such as exact plug type and symptoms—to validate the claim.