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P0135 - Bank1?

11-16-2010, 04:21 AM
I just got a 99 Camry with the engine lite on & it spits out P0135 - sensor heater circuit Malfunction (bank 1), with 2 of the same error showing. Does this mean two O2s are bad? How many does it have? I borrowed my friends obd2 reader.

I searched & know it's an O2 sensor, but what's bank 1? Looking at the threads here, there's up & downstream. Which one is bank 1? Where is it located & how can I get to it?:screwy:


11-16-2010, 11:17 AM
I believe Bank 1 is the sensor before the catalytic convertor.

Have you tried (

Good luck,


11-16-2010, 12:51 PM
If you have the 6-cylinder engine, bank 1 sensor 1 is the upper oxygen sensor (before the cat) for the firewall side bank of cylinders. This is a heating circuit failure for the sensor, so if the sensor's heater checks okay for resistance, then check the wiring and connections.

For the 4-banger, there is only one'll be mounted in the exhaust pipe just downstream of the header in front of the engine before the downpipe connection flange.

11-16-2010, 07:21 PM
Thanks guys. It's a v6. It showed 2 errors but it was the same code for both. Do you know how may of this bank 1 O2 does it have? I checked rockauto & it's about $72 each, wow! I still need to do a tranny flush cause it's black already, plus the insurance, transfer, etc. The horn doesn't work even though it's new, need to figure that out. Plus I have a power steering leak. :banghead: So I hope it's only 1 O2 that I need to change.

I'll post my findings here when I get to it.


11-16-2010, 09:50 PM
The "bank" refers to each row of cylinders in the engine. A 4-cylinder has one row, thus only one bank. A V6 has two rows, thus two banks.

In the exhaust piping, before they are combined into one pipe, each bank has a separate catalytic converter and two oxygen sensors after the exhaust sensor before and one after the cat. So a 4-cylinder will have one cat and two sensors...a V6 has two cats and four sensors total.

The OBD system is able to discern which one is having troubles, but cannot discern if it is the sensor itself or the wiring, connectors, etc.

You can test if it is the sensor itself by switching it with the pre-cat sensor in bank 2, or you can probe it with a multimeter. If the error shows up in Bank 2, then it is the sensor...if not, it's the circuit.

As for the horn, check to see if the horn fuse is blown.

As for the black tranny fluid, I would suggest against a power's been known to cause transmission death due to it dislodging particles and redepositing them into the valve body. Instead, drop the pan and drain the fluid, clean the pan magnet, and change the filter. Refill it and run it for a few hundred miles. Then drain & fill it it a few hundred more miles, then drain & fill again. This lets any buildup redissolve and be removed slowly and be caught by the filter.

As for the power steering leak, I've used Lucas Power Steering Stop Leak with success.

Hope this helps!

Brian R.
11-17-2010, 07:10 AM
Oxygen sensors go bad with time. It is most likely the sensor is bad and needs to be replaced. Call a Toyota parts department and give them your VIN number to get the correct part number for the sensor. There are usually more than one sensor installed in Toyotas of any particular year so you better make sure you get the right one. Get a DENSO unit from Amazon. I think they are the best buy in town...

11-18-2010, 06:30 AM
Thanks guys for the bad news. :shakehead I was hoping it would only be 1 sensor, but I should've known, it's a v6. So 2 sides, 1 on each side. Thanks jdmccright for the great details of tips.

I'll let you all know what I find after I check where the sensors are at.

Brian R.
11-18-2010, 09:32 AM
Just replace the sensor referenced in the DTC. Unless you have two codes, each referencing a different sensor, you only need to replace the one in the DTC.

11-18-2010, 09:33 AM
Each sensor is wired separately into the ECU. Though logic (and Murphy)may dictate to replace both of the pre-cat sensors (Sensor 1 of Banks 1 and 2), you should only need to buy one sensor if you're in a pinch to pass an emissions test. Eventually the opposite sensor will probably fail, and you can belay that purchase, but be prepared for it to come.

The sensors after the cat (listed as Sensor 2) do not need replacing.

11-19-2010, 07:31 PM
Ok. I took some pictures and I hope this will help those with the same problems. I was trying to post it in my gallery and link it to here but it kept giving me "mysql error". So I just did attachments.

There is one right after the cat before the muffler - I believe this is the downflow one. This is located underneath between the front seats. You can't miss it when you stick your head underneath.

I pop the hood open & wow! It's just sticking out right below the exhaust manifold. Awesome!! This must be one of the upflow one.

Then the bummer one. This is way low right before it becomes one tube & into the cat. And it's close to the firewall.

I guess I can reach down there and feel around with a wrench. But if the angle is odd when the wrench gets on it, I might not be able to turn it. Maybe an angled wrench might work. Then it's a matter if my arm would be in a position to be able to turn it & not scrape or crush my fingers. Any suggestions?

But which one is bank 1? Is it from front to back? I hope so, then it's the easy one.

I also checked the fuse to the horn & it's good. I think the guy who I got it from said he tested if power was going to the horn & there's power. I also checked the fuse box in the cabin & there's none for the horn. I think the horn went out when the cruise control went out, at the same time. Could it be the steering wheel? My previa horn will work when it feels like it. Maybe this is a Toyota thing.

I rubbed my eyes & reread jdmccright's detailed tips about the tranny & really don't want to drop the pan. Can I just change the fluid for now? I won't flush it. I just don't want to get the gasket & find the torque specs, and blah blah blah.

The power steering pump was changed few months before I took it over. Probably a hose gave out with the right pressure now. A drive around town would leak a lot, this should make it easy to trace, hopefully.

I checked out ( (with a 'y'). Thanks! A bunch of manuals at the click of a button. I skimmed through for O2 in the emissions section but couldn't find it. It's mainly about egr, pcv, etc.

I'll post anything else I can find as I take on this project.

One other thing, DON'T LOOSE THE BLACK KEY! I want to stress that out because that is the MAIN key that will open all doors & trunk. This is also the key you'll need if you need a replacement FROM the DEALER. It has a chip inside it. Without this, the car won't start. I only have the Grey one and it doesn't open the trunk. The dealer can't do a replacement with this key. You would have to replace the whole ignition with matching keys if you loose both, which means $$$$$. Remember, it won't start, so you'll have to tow it and, you get the picture.

11-22-2010, 03:29 PM
Bank 1 is the one between the engine and the firewall. Bank 2 is the easy one.

Yes, you could just drain and fill the tranny, but remember there is a magnet in there to clean, too. If it gets too gunked up, it can't remove the fine metal particles from the new fluid like it's supposed to. Plus, the filter has probably got a good amount of trapped particles from all those years of neglect. Be aware of this and decide for yourself.

You really don't need a torque spec for the pan or filter bolts, though it helps since they are bolted into aluminum. Just hand tight with a 3/8" ratchet or box end wrench is sufficient. You're better erring on being too loose than too tight...easier to stop a leak than to replace a crushed gasket or rethread a stripped bolt hole.

Good luck!

11-24-2010, 07:28 AM
Thanks, that just made my day. Can I just say to myself "bank 1 is the easy one?"

11-24-2010, 09:02 AM
Absolutely...just repeat it to yourself with happy thoughts as you blindly reach deep down behind the engine and slowly and tortuously scrape the skin off of your knuckles (anybody else getting "Saw" flashbacks here?).


In reality, even the "easy" ones are never easy...there's always something else you've got to move or remove first, or a bolt is frozen and breaks off, or you drop a piece into a tiny nexus that not even a magnetic probe can get to. Murphy LIVES in the garage...he's your assistant whether you like it or not.

Good luck!

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