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Discussion Starter #1
My Rav is 2007 base 4wd with 98k miles.
I got CEL, VSC, 4WD lights on. Scanned code P0138, bank1 sensor 2 voltage is too high. I replaced post cat O2 sensor to new Denso O2 sensor. But the same lights and code came back soon.
Below are the recorded graphs while I was driving with new O2 sensor. AFR looks okay. Still O2 sensor output voltage stuck to 0.9V. It went low boltage only when I released the accel pedal in decending slope.
What else can I look?

Thanks.
 

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According to your profile you have the I4 engine.

You might get some useful information from this thread. It includes links to a troubleshooting chart, and some tips on proving if your problem is caused by a defective sensor, or a problem in the wiring.

The final solution to this earlier problem was a defective B1S1.
 

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I have the same problem, same code. Did some of the troubleshooting from the link posted, new Bosch O2 sensor.. I unplugged the sensor, got a low voltage code and no output, which is correct..if you figure it out post it please thanks..
 

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It was bad Air/Fuel ratio sensor.

The OBD data log showed long term fuel trim is +7% or more even though AFR sensor output is in good range.
AFR sensor output shifted to lean and ECM was fooled and injected more fuel.
That's why O2 sensor stuck rich.

After replaced AFR sensor, CEL/VSC/4WD lights were gone and fuel trim%, AFR, O2 data is in normal range.
 

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Discussion Starter #6
My Rav4 is 2007 2.4L base. A/F ratio sensor I bought is Denso 234-9041.
Look for yours in
Find My Part | DENSO Auto Parts

I also got an error code P2195 once before I got P0138 numerous time.
P2195 had never come again so I went O2 sensor first and wasted time and money.
 

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That code drives me mad. Searched around the forum and changed B1S2. The code still came back. Do you have any idea what else should I look into? AF sensor, ECM?
 

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I also replaced the B1S1 Air Fuel Sensor before the Catalyst and it took care of repeat code P0138. 07, 4 Cyl. 115K miles..
 

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What is the Part # for the sensor B1S1? I also have this error even after replacing the sensor 2, might give it a try.
 

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Hey this was a great feed. So, I am stuck with either taking my car to toyota and pay 110.00 for diagnostic test of code p0138. Mind you, already changed downstream oxygen sensor with denso but code came back on after 30 miles of driving. After reading this forum, i am somewhat convince I should buy air fuel sensor but this isnt cheap either, wopping 200.00 dollars and cannot be returned. So, I am torn, whether to pay toyota 110.00 or use that money towards A/F sensor upstream, whats your say?
I just dont to waste my money going to the dealer and telling me what i already know and replace the oxygen sensor that i have already replaced with their own which means by the way throwing more money.
Well, buttom line, Im going to buy A/F sensor and hope for the best. Thinking of doing this tomorrow Nov.23, 2015
 

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It was truly was the A/F air fuel sensor upstream though the code from OBDII calls for p0138 (oxygen sensor downstream). Dont go to Toyota they would've milk me for a lot of money: diagnostic test (110.00), new oxygen sensor 100.00 and air fuel sensor 200.00 not including labor of course. Trouble shoot what u got on hand, if ur handy, at least for me, it worked out, hope it'll do the same to u
 

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I had the same problem a few months ago. I took it to dealer (Bought extended warranty from Jerry at Mid West Toyota) and they replaced oxygen sensor. One day later VSC and CEL light back on.

Took it back and AF sensor was replaced. No problems since.

Glad i bought the warranty from Jerry and glad i joined this forum because that is where i found out about the warranty at great price.
 

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I also got P0138 from DMV inspection. VSC CEL 4WD been steady 'on' for few months (few days after dealer recall visit!!). My problem is I rarely drive-9yrs with 68k!
 

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Another P0138 solved: replaced B1S1 A/F sensor (not O2)

It was bad Air/Fuel ratio sensor.

The OBD data log showed long term fuel trim is +7% or more even though AFR sensor output is in good range.
AFR sensor output shifted to lean and ECM was fooled and injected more fuel.
That's why O2 sensor stuck rich.
After replaced AFR sensor, CEL/VSC/4WD lights were gone and fuel trim%, AFR, O2 data is in normal range.
Appreciate you starting and solving this P0138 trouble code. It cropped up on my 2009 I4 and the indicated problem is the B1S2 02 sensor. But the real culprit was B1S1 A/F sensor. Thanks to this thread I went straight to the A/F sensor replacement. For the 2AR-FE engine (I4) the Denso part is 234-9022. DIY not extremely difficult, cost of part online $92.
 
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