P1155 & P0161

My AutoTap diagnostic software/hardware shows these errors as:

P0161 Heated Oxygen Sensor Heater Circuit (bank 2, sensor 2)
P1155 Alternative Fuel Control Module Has Activated the MIL

I cleared the codes, but almost instantly the P1155 returned. The description provided by AutoTap does not indicate which sensor is the culprit, however, in another thread here, P1155 is defined as:

P1155 A/F Sensor Heater Circuit Malfunction (Bank #2 Sensor #1)

This question must have been asked a million times, and I simply can't find the answer... but which sensor is B2, S1? And, when I order generic parts, how do I make sure that I grab the right one? According to some technical papers I've found, an A/F sensor is quite different from a regular O2 sensor - it apparently has a much wider range... so, going to a parts store, what do I ask for?

I have found four sensors and their connection points (two on each side of the exhaust manifold). I've disconnected them one at a time, cleaned the terminals, and reconnected them. There are four terminals on each plug. Two seem to be for resistance, the other two for voltage. One of them reads all over the place on with resistance (tested with engine running, sensor unplugged from harness, and testing directly at the sensor connector terminal).

I have an extended warranty for this Rav4 (2002, 2wd, Florida, 50k miles) through Warranty Gold - who has, of course, gone out of business after taking my $1200 premium. Oh well...

[AussieRAVer]

OK, you need 2 sensors -
1 A/F ratio sensor
1 O2 sensor

the right side of the exhaust manifold (Looking at the engine from the front of the car) is BANK 1 - Cylinders 1 & 4

the A/F sensor goes BEFORE the CAT converter - THE TOP
the O2 sensor goes AFTER the CAT converter - THE BOTTOM.....

also, when replacing these sensors run the car a little to warm up the manifold - when cold you will probably damage the threads....

hope this helps

Thanks Aussie! That's a great help... I also need to know how to differentiate between an A/F and O2 sensor when I go to my local (or on-line) parts store. They all seem to call them O2 sensors, regardless of which one I need... It's a bit daunting to plunk down >US$100 for something that may not be compatible. I just don't want to go to the dealer for a $250 part.

Also, is it possible that the P1155 error is causing the OBDII to report the P0161 error? I cleared both DTCs and the only one that keeps coming up is the one for the A/F... Just wondering if I should try to replace only one first, to see if the second one comes back. In doing so, could that ruin the one I change?

Anyone know what the diff between the left and right A/F sensor is? I've found a Bosch replacement A/F sensor, but it's right side (B1,S1) only... if it's just a matter of the cable length, I'm sure I can cut/splice the old cable to it.

[AussieRAVer]

Check out this
http://www.toyautoparts.com/TO_Air1b...nsor_list.html

Enter you model year, then select your RAV type (This step doesn't really matter - the engine is the same....) then go down to the FUEL INJECTION section.... select the AIR FUEL RATIO SENSORS..

Ive had a quick look at 2002 models and there are 3 available - 2 right 1 left.... you are looking at $200 +/- each

[rav4-22102]

P1155. so the heater circuit is bad. does it have to be fixed? what will happen if i don't fix it?

Originally Posted by rav4-22102

P1155. so the heater circuit is bad. does it have to be fixed? what will happen if i don't fix it?

Oxygen sensors (wether they are narrow or wide band) operate at elevated temperatures. When your engine is cold, electrical current is passed through the sensor heater in order to be able for it to give a reading to your ECU.

Once your engine is run for a little while, exhaust gas will keep the sensor hot enough, providing your are not idling.

Driving with a damaged heater will result in loss of fuel economy since it will take a lot longer for your sensor(s) to heat. Both A/F sensors heater broke on my girfriend's rav4 and the difference is significant + not good for carbon deposit in your engine.

Just as a reference: As seen from front of car (I will post picture shortly)
P1135 upper right - toyota part# 89467-42010 - Denso part# 234-9023
P1155 upper left - toyota part# 89467-42020 - Denso part# 234-9028
source: http://www.benitomo.com/CATALOGOS/De..._Reference.pdf and verified in person.

Here it is, as seen from the front of the car once the heat shield is removed.

Both A/F are circled yellow and red (sorry for such small circle but I've only got paint)

[img][/img]

[rav4-22102]

Thank you, FredEng22. That was very helpfiul. I will try to replace this myself. I hope getting the heat sheild off isn't a pain. (2003 Rav4)

The heat shield is the easy part, 3 12mm bolts and a 12mm nut will make it loose.
They are all in front either on top (3) or towards the ground (1).