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Discussion Starter #1
I have an 03 SR5, 4.7, with 134,000 miles. The engine still has the original 02 sensors. I've never had a code on them but after I installed iridium spark plugs, the mileage dropped. If the sensors should be changed, is there a particular brand that works best for this engine?

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You aren’t throwing any codes?

I used Denso from Amazon with good results (code didn’t come back)

I can’t link to it, but I made a blog post with some pictures.

Here’s the text:

My 2004 Tundra check engine light was on. I checked the codes and got P0135. This is the driver's side left front sensor. Since once side needed done, I decided to do both banks.

Oxygen sensors were ordered from Amazon Denso 234-4169 for $41.85 each versus the local autoparts store price of $80 each. Make sure you use Denso sensors, like Toyota did. The Bosch will continue to throw the code. The Denso part referenced also is NOT universal meaning you don't have to splice the wires.

Denso 234-4169 $41.85 Amazon
Oxygen Sensor Socket 7/8" $10 Autoparts Store
PB Blaster or WD40

P0135 Driver Side Bank 1 Sensor 1
P0155 Passenger Bank 2 Sensor 1

Finding the Sensors:
There are upstream and downstream oxygen sensors. Downstream oxygen sensors are after the catalytic convertor. If the codes are above, then the sensors are upstream. Find the exhaust and you will see the front crossmember. The drivers side is behind the exhaust flange.

How to Fix:
1. The upstream sensors are on the end of the exhaust manifold, behind the front crossmember.
2. Soak the sensor with PB Blaster or equivalent
3. Unplug the electrical sensor connection. This was by far the hardest part, since you can only reach one hand. I wedged a small screwdriver in the tab to disconnect.
4. Remove the sensor using the socket. My engine has 150,000 miles and this wasn't difficult. Some sensors have seized in, but I got lucky.
5. Apply anti-seize (supplied with Denso sensors)
6. Install new sensor and torque 32 ft/lbs (Toyota Service Manual)
7. Connect electrical sensor connector
8. Disconnect Negative terminal of battery to clear the code.
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