O2 Sensor Replaced - Engine Light Has Come Back On

[Pastie]

I've recently had all 4 of my O2 sensors replaced (at a non-Toyota garage to avoid the £90/hour labour rates that Toyota charge) on my 2002 GX 2.0 petrol manual.

Had the engine warning light reset but this came back on a couple of months later. Had a diagnostic performed at my local Toyota dealership and it was showing O2 Bank 1 Sensor 2 failure. Went back to the garage that had fitted the part and they replaced the sensor free of charge as it was within 12 months warranty.

14 months go by and the engine warning light comes on again. Back to Toyota for another diagnostic and lo and behold.......O2 Bank 1 Sensor 2 failure!

Again went back to the garage and they told me it would be very unusual for a sensor to fail so quickly (the originals lasted 45K over 9 years), but they agreed to replace at cost.

Had this done yesterday and the engine light reset. Drove 20 minutes home, no issues. Restarted my car this morning....engine warning light is back on!!! Not had a diagnostic done yet, but I can only guess that it's good old Bank 1 sensor 2 again.

To have the same O2 sensor fail 3 times must be high on impossible, so does anyone have an idea as to what else this could be caused by?

My gut reaction is to go back to Toyota and ask for a free diagnostic, but if that confirms Bank 1 sensor 2...what next?

[Joylove]

Are you using the correct and Geniune Denso part? They have different resistances for the heater coils for pre cat (~4R) and post cat (~15R). You can measure them with your multimeter in minutes for peace of mind. If so there was talk of an ECU upgrade.

[mystic]

maybe a faulty cat?

[Joylove]

Also there was talk of possible faulty Grouds to the sensors causing high resistance. Start by checking the sensor with your multimeter then move onto the GND and the SW update.

[Pastie]

Thanks for your replies.

Joylove - I'm a complete novice, so please excuse my daft questions - what are the GND and SW update? What would these multimeter checks show if there were faulty grounds to the sensors causing high resistance, and what would the solution be if this was the case?

Cheers.

[Joylove]

Check out the first link in my sig for the heater coil measurements. As I understand it GND (ground) is one of the black vehicle wires. Between a good clean ground in the engine bay and one of the two vehicle side black wires it should be almost a dead short. Allegedly. Then the heater coil resistances are in the first link in my sig, the two black wires are the heater coil.

Do your tests with the Battery unplugged and expect rough idle for the first 80-100 miles after reconnection during the learning phase.