P0138 code problems - Page 3 - Toyota RAV4 Forums
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post #21 of 34 (permalink) Old 02-26-2014, 01:20 PM
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Yes, I'd be suspicious of changes to wiring and possible programming. Suggest getting the details.

On the sensor data readings I'd be sure if the scanner is reading what you think it is.
The .3-.5V is what I'd expect for pre-cat AFR sensor. A post-cat wideband 4-wire one shouldn't read the same.

Fred
2006 RAV4 V6 4WD Red Limited - wife's
2006 Accord V6 Hybrid - Dr. Dyno's - quick as the RAV but +8 mpg
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It's the pedal (or the handgrip) on the right!!


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post #22 of 34 (permalink) Old 02-26-2014, 06:51 PM
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An addition to my recent post...

At this siie I found the following.
O2 Sensor FAQ
In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire.

But the question though, FROM the vehicle wiring does Toyota have a bias voltage as well, if so, what is the voltage?

Not looking for info about the initial Air/Fuel sensor, it's always trying to achieve 3.3 volts.
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post #23 of 34 (permalink) Old 02-26-2014, 09:23 PM
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Originally Posted by Rav4tech View Post
At this siie I found the following.
O2 Sensor FAQ
“In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire.”
I read that article and question what he means by a "modern" car since it only discusses the narrowband AFR sensor. The .45V, which I never heard of, could only be a test signal since if it was an actual full time bias it would defeat the sensor's high impedance 0-.7+V output especially on what must be a one-wire sensor. Today's heated sensors both narrow and wide band ALL have four wires, not the two or three he mentions. His explanation most certainly applies to pre-OBDII cars.

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But the question though, FROM the vehicle wiring does Toyota have a bias voltage as well, if so, what is the voltage?
Maybe I'll get time to look it up but I doubt it'll spec the voltages.
Quote:
Not looking for info about the initial Air/Fuel sensor, it's always trying to achieve 3.3 volts.
Just wondered what your source for the 3.3 volts is.

Related: I'm about the replace the four-wire post-cat sensor on a 4.1 RAV4 for the THIRD time. The original one had no issues for 120,000 miles until it got damaged during exhaust system work so I replaced it. After maybe six months the CE light came on & codes said "open in heater circuit." Replaced the sensor with another Bosch one. That lasted maybe a year. Light on again, same heater code. This time I used the pin-thru-the-wires method to check for 12V with everything connected. It is there between the gray wires. Disconnected the sensor. It's open between the gray wires. Have the third one here on my desk but since the car just passed emissions (with the light off) I think I'll wait until we get ready to sell it before installing it. Point is new sensors do go bad.

Fred
2006 RAV4 V6 4WD Red Limited - wife's
2006 Accord V6 Hybrid - Dr. Dyno's - quick as the RAV but +8 mpg
2003 Odyssey V6 - handy people & cargo mover
1999 F-250 4X4 Diesel - snow plow, Bully Dog chip
2001 F-250 4X4 Diesel - truck camper, TS chip, 20' bike/trike dyno trailer
2004 Suzuki DRZ-400S Dual Sport
1968 Volvo 1800S

It's the pedal (or the handgrip) on the right!!


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post #24 of 34 (permalink) Old 02-27-2014, 12:10 AM
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Quote:
Originally Posted by Rav4tech View Post
At the 4 wire connector FROM the vehicle, one wire has 12v for the heater, guessing 2 other wires are eventual grounds, but isn't the 4th wire suppose to have a reference voltage for the O2 sensor? Something like .3 to .5 volts?
It looks like the black wire is the 12V supply to the heater (PIN #2 on the sensor). The ECM applies ground to the other side of the heater on the red wire (PIN #1). If you disconnect the sensor from the cable, you should read the heater resistance of 11-16 ohms between pins #1 & #2


The ECM monitors O2 levels between the black and brown wires on pins #3 & #4. I'm not sure how that measurement is made though. If it helps pin #3 is connected to the OX1B signal of the ECM and pin #4 is connected to the EX1B signal connector. With the sensor disconnected you should read greater than 10K ohms between pins #1 & #4, I think this test shows that no leakage exists between the O2 circuit and the heater circuit.

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post #25 of 34 (permalink) Old 02-28-2014, 11:26 PM
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I didn't see where it mentioned 'modern' car.

It does state "if the circuit is not complete, the computer picks up a steady 0.45 volts." Possibly indicating if the O2 sensor was unplugged the computer would see .45volts from somewhere, not the O2 sensor.

I was just hoping someone would go out to their Rav4, unplug the rear O2 connector and check the voltages from the vehicles connector, key on of course.

Regarding the 3.3volts for the A/F sensor.
Go to Automotive Training and Resource Site click "Technical Articles" in the left column. Then scroll down and click on article #37 regarding Oxygen Air/Fuel sensors. Read the first 11 pages. The Air/Fuel ratio operation is described beginning on page 6, referencing the 3.3 volts.

Also note: at the bottom of each page it indicates copyright by Toyota Motor Sales.
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post #26 of 34 (permalink) Old 02-28-2014, 11:43 PM
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The heater circuit appears fine. Bench tested the old O2 sensor, it apprears okay, not lazy when changing voltage and the heater shows about 14 ohms.

The O2 sensors we have here: 2 white wires for the heater, a black and gray for the O2 sensor voltage.

Next time I'm over near the Rav4 i'll check for continuity to/from the O2 sensor at the ECU since the ECU is readily available under the hood.

Thanks for responding.
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post #27 of 34 (permalink) Old 03-01-2014, 11:00 AM
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Quote:
Originally Posted by Rav4tech View Post
I didn't see where it mentioned 'modern' car.

It does state "if the circuit is not complete, the computer picks up a steady 0.45 volts." Possibly indicating if the O2 sensor was unplugged the computer would see .45volts from somewhere, not the O2 sensor.
While describing testing for the .45V he uses the term "most late model cars" in the body of the article and starts by saying "These procedures are only for self powered conventional (one-wire) sensors. Some very new cars are using a different style sensor that is powered." Since the last turbo Regal on his forum was made in the late 80s and one-wire sensors are long gone, what I'm saying is altho some of the info still applies to 14.7 narrowband sensors, don't expect to find the .45V readiness test signal anywhere on a four-wire wideband sensor.

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I was just hoping someone would go out to their Rav4, unplug the rear O2 connector and check the voltages from the vehicles connector, key on of course.
Would be nice but you do realize that's it's 20 degrees in the northern states and most of our members wouldn't have a clue how to do what you suggest.

Quote:
Regarding the 3.3volts for the A/F sensor.
Go to Automotive Training and Resource Site click "Technical Articles" in the left column. Then scroll down and click on article #37 regarding Oxygen Air/Fuel sensors. Read the first 11 pages. The Air/Fuel ratio operation is described beginning on page 6, referencing the 3.3 volts.
Excellent article and I see the confusion. He refers to what I'd call a narrowband sensor that's used to set the engine's AFR as an "oxygen" sensor, and what I call a wideband one that's used to read the engine's AFR after the cat, as an A/F (AFR) sensor. That's where you're getting the 3.3V which is correct. And altho I believe the nomenclature "oxygen" and "A/F" sensors may be common in the industry, I still prefer narrowband and wideband to distinguish them since technically they both measure oxygen content just in different ranges. But I'll have to remember their terminology when talking to automotive techs just like I do keeping track of black and white in electrical or electronic wiring.

Quote:
Also note: at the bottom of each page it indicates copyright by Toyota Motor Sales.
Sure would like to have dates for both articles. I guess the Regal forum one is about 1990; the Toyota, 1995.

The wideband AFR sensors my dyno uses to get it's fuel graphs are five-wire. The fifth wire is for a built-in calibration resistor to compensate for manufacturing tolerances. Five-wire sensors have been used on some "modern" cars for ten years.

Fred
2006 RAV4 V6 4WD Red Limited - wife's
2006 Accord V6 Hybrid - Dr. Dyno's - quick as the RAV but +8 mpg
2003 Odyssey V6 - handy people & cargo mover
1999 F-250 4X4 Diesel - snow plow, Bully Dog chip
2001 F-250 4X4 Diesel - truck camper, TS chip, 20' bike/trike dyno trailer
2004 Suzuki DRZ-400S Dual Sport
1968 Volvo 1800S

It's the pedal (or the handgrip) on the right!!


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post #28 of 34 (permalink) Old 03-01-2014, 11:35 AM
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Quote:
Originally Posted by Rav4tech View Post
The heater circuit appears fine. Bench tested the old O2 sensor, it apprears okay, not lazy when changing voltage and the heater shows about 14 ohms.

The O2 sensors we have here: 2 white wires for the heater, a black and gray for the O2 sensor voltage.

Next time I'm over near the Rav4 i'll check for continuity to/from the O2 sensor at the ECU since the ECU is readily available under the hood.
Wow, more confusion! You are calling the post cat wideband sensor an "O2 (oxygen) sensor" not an A/F sensor as in the Toyota article. And the invoice with the new post-cat one I have on my desk lists it as a "new premium high performance O2 oxygen sensor Lexus Toyota." (BTW, it's heater wires are white, not gray as I posted earlier.) I do think you know what you're doing and continuity tests are next, but don't expect to see .45V anywhere on your wideband sensor.

My guess, a new but bad sensor.
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post #29 of 34 (permalink) Old 03-09-2014, 05:17 PM
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Originally Posted by wake_100 View Post
you mean multiple sensors? with the 2.4 there is only 2 sensors. I checked the sensors for resistance and they check okay as per service manual but we'll say something is on sensor one (upstream) that wouldnt change the value of the resistance I think. I think if sensor one was coated in soot it would make it rich making sensor two high voltage?

I am wondering about my vacuum system in it to. I can sit at a stop light, and just stretch my leg pressing the brake pedal and I can set of the stability control. it'll beep and the light of the car with skid marks under it will light up. can reproduce it 100%
I am having the same problem with my Rav. I changed the downstream sensor and kept getting the p0138 code. Now I was gonna change the upstream one(as the dealer suggested) but it tests Ok by multilmeter for resistance. I afraid that this will not fix the issue. Do you have anydate on your car after replacing the upstream one? thnx
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post #30 of 34 (permalink) Old 05-05-2015, 06:12 PM
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2011 rav p0138 code

so i changed bank 1 senser 2 high voltage o2 senser didnt fix problem warning lites back on in 40 km some one said i should change the air fuel senser as well thats probably the problem !but wouldnt air fuel senser show a different code then po138 ? the a\f senser is twice as much money as the o2 senser that my code reader said was wrong !i dont want to go to toyota i know it will cost a fortune !it has 100km 4 cyl !im really disliking this rav and as soon as its repaired im selling it !i do love my 98 rav ! is this comman problem with all ravs or just mine !thx people

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