The scan tool is not able to perform O2 sensor tests on 2 of the 3 sensors. The one it does test is the O2SB1S2.
Also, I captured "Live Data" readings off the OBD-II and see Bank1Sensor1 O2S voltage of 3.96 Volts, and Bank2Sensor1 O2S voltage of 3.99 Volts. Whereas the Bank1Sensor2 voltage reads 0.8 Volts.
Haynes repair manual for Highlander indicates that the V6 2001 has 3 O2 sensors, of which 1 is downstream.
I would like to add that about a month ago, I replaced the BATTERY on the Highlander myself (auto zone). The battery was easy to replace and I did not have to juggle with any other cables etc. I hope I did not juggle something then.
Q1) Does all of the above information point to the (one and only) downstream sensor (B1S2) just ahead of the first muffler?
Q2) If so, is this really on O2 sensor or A/F (Air/Fuel Ratio) sensor?
Q3) If I have to replace it, do I have to remove the back seat and carpet to access it (as mentioned in Haynes guide), or can i disconnect cable from negative battery terminal and then access the sensor from under the car (which it seems is under the driver's seat as opposed to the rear seat).
Q4) On The Other Hand, is the B1S2 voltage of 0.8 valid? I.E. Is the voltage of a sensor proportional to the oxygen level, meaning does the low voltage indicate of B1S2 indicate a valid reading? Implying the catalytic converter is doing its job?
If needed, I can post more LiveData and/or FreezeFrame scanned information.
The downstream O2 sensor has an heated element to get the sensor up to temperature, these O2 sensors must be hot to work. So it sounds like the heating element in bank 1 downstream O2 sensor is burnt out. When the O2 sensors are close to the engine they get hot enough from the exhaust manifold to work and do not need a heating element.
The computer monitors the amount of oxigen in the exhaust to properly set the fuel/air mixture, so that is why you are getting that A/F sensor heater circuit malfunction.
Check with your dealer, this is an emissions system element so you might be in the 80,000 emissions warranty at 70,000 miles.
I checked the warranty booklet and see that the Catalytic-Converter is covered for 8yrs/80Kmiles. I will check with the dealer regarding the O2 sensor. If it is covered I hope it implies parts and servicing.
If anyone knows of any website that gives more detailed info on toyota warranty, please post.
I re-read the Warranty. It seems Federal requirement for Emissions Warranty is for 2yrs/24Kmiles, but Toyota provides emissions warranty for 3yrs/36Kmiles. However certain parts are warrantied for 8yrs/80Kmiles, and these include (1) Engine control module, (2) CC and protector, (3) Data link connector, (4) Malfunction indicator light and bulb.
So, I am not sure whether the O2 sensor is included in the warranty, but, I will ask them anyway.
N.E.O. Thanks for the post. I had read some other post about A/F sensor on some other thread (maybe it was yours). Is there any way to tell whether it is B1S2 or B2S1? In other words how do you (did you) determine the bank# and sensor# given the code P1155?
Also, where is the A/F sensor located? I don't see any entry in Haynes.
Are the O2 sensor voltage readings correct? 3.98 volts for upstream ones, and 0.8 volts for the downstream one? Is the voltage directly proportional to the amount of oxygen? If so, then if the CC is working properly, then the voltage on the O2 B1S2 should be low. However, there is a test (minVoltage maxVoltage) on the Innova 3130 and the results are confusing.
The A/F sensors are pre-cat sensors, and the code you had, P1155 is for bank 2 sensor 1. Bank 1 is always the cylinder bank where #1 cylinder is located, and in your case if would be the back cylinders. Sensor 1 is located on the exhaust manifold.
The normal voltage reading for the A/F sensor is aprroximately 3.30V, and the reading will vary up and down from there. 3.98 is too high, rich mixture; however, that could have been affected by the heater element not working properly, hence the P1155.
The O2 sensor in your case, which is the post cat sensor, is used the monitor the cat's efficiency, its voltage varies from 0 to 1.0V, depending on the oxygen concentration. Don't quote me on this, I think it is inversely proportional to the oxygen contain, a lean mixture will have higher oxygen concentration and a rich mixture will have less.
The 3.98V readings (ON BOTH sensors) was when the vehicle was stationary and recently turned on. I took some live readings when driving and saw the readings to be around 3.3V or so, but I will confirm and re-post or edit this posting.
So, what I hear you saying (and as per the link above) Highlander has TWO A/F sensors upstream (also known as wide-band oxygen sensors), and ONE normal/narrow-band Oxygen sensor downstream.
It could be either the sensors (both sensors have 3.98 V on startup) or the relay???? Hmmmm.... For now I am going to test drive get some readings.
P1155 is only for bank 2 sensor 1; bank 1 sensor 1 has its own code, P1135, and so does the O2 sensor, P0141, but they are all just for the sensors' heater circuits. In this case you don't look at the sensor voltage since it is the sensor's heater that is not functioning properly. you can measure the resistance of the sensor's heater element to see if it is in spec or if it is open. The reason for the code is because the ECM is not seeing the correct amount of current draw from the sensor's heater element. Since only one code is store, the relay that supplies the power tow both A/F sensor heater is probably functioning correctly.
It is possible that the codes on the links I sent are for US models, but the one in the Camry manual are for California model. My Highlander is a Calif model, so it suits me just fine. Also, my highlander has the 1MZ-FE engine, which is the same as the Camry. I was thinking of checking the code from the local library (if they have the prof repair manual), but your link suits me just fine.
So, it seems P1155 is Bank 2 Sensor 1 A/F Ratio Sensor Heater!
Also, during the recent LiveTest, I see "Fuel System 1 Status" is ClosedLoop and "Fuel System 2 Status" is OpenLoop.
So, Bank 2 Sensor 1 is on the rear exhaust manifold accessed from beneath the car.
I believe Toyota uses Denso sensors (OEM), so maybe I'll go for that (or buy from a dealer).
Additionally, I might erase the code, and see if it reappears...
Bank 2 is actually the front bank, with cylinders 2, 4, & 6, which is what you code is for. You should be able to see the sensor on the front exhaust manifold by the cooling fan.
Even though the link is for a Camry, the test is still valid for your vehicle. The reason it states Cal spec vehicle was during that model year the Fed spec vehicle used O2 sensor as sensor 1 while the Cal spec vehicle used A/F sensor as sensor 1. The Highlander had always used A/F sensor for sensor 1.
Erasing the code won't hurt if you like to verify the code. Do stay with Denso or Toyota sensor, might cost
a little more but less chance of complication.
My suggestion is to simply test the heater element in bank1 sensor2 O2 sensor with an ohmmeter to see if the element is indeed open. As the error code says "heater Circuit Malfunction" that suggests an open heater element or loss of +12 volts to heat the element itself. Just remove the O2 sensor connector and see if the heater element is open or if there is +12 volts to heat the element.
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