Error P0135 Sensor Heater Circuit Malfunction

Error code P0135 is "O2 sensor heater circuit malfunction bank 1 sensor 1. Automotive sensors are generally described by what they are supposed to sense, i.e., oxygen, air flow, coolant temperature, etc.

Although I always recommend that someone check a component before checking it, I seem to hear of problems with this sensor often enough that swapping it out is probably not a bad bet.

Bank 1 sensor 1 will be in the exhaust manifold on the side of the engine closest to the firewall. Reaching it is the biggest challenge, otherwise, unsnap the connector, and righty tighty lefty loosey to remove and replace the O2 sensor.

I can get a part like this at a typical car parts store, right? Thanks for the quick reply.

Yes, you can get an O2 sensor at a typical auto parts store, although I personally prefer genuine Toyota parts.

One more question concerning this. How will this sensor not functioning properly affect my car?

One more thing...I was doing some research and I found that there are oxygen sensors for before or after the calyltic converter. Do I need to replace both? They are listed as 64$ or 130$. There is a large difference in the prices of them. Besides the warranty, is there any real difference in the mechanics of the two?

Thanks again, Stephen

Basically, the oxygen (O2) sensor measures the amount of oxygen in the exhaust gas and reports the O2 levels back to the engine computer. The computer uses the information to adjust the air/fuel mixture.

On systems with O2 sensors before and after the catalytic converter, the one after the cat is monitoring whether the cat is doing its job or not. Vehicles with an OBD II system use this setup. The OBD II diagnostic system is primarily designed to control emissions.

An O2 sensor needs to be heated to over 600 degrees Fahrenheit to operate properly so a heated one has a heating element inside to get to this temperature much more quickly than waiting to get heated by exhaust gases. The quicker the O2 sensor gets to operating temperature, the sooner the computer has the info it needs to reduce emissions.

The trouble code you mentioned means that the heating element in the sensor isn't working so exhaust emissions may be too high. You may or may not discern reduced engine performance.

You only need to replace the bad O2 sensor. There is no need to replace ones that have not set a trouble code unless you have failed an emissions test or notice poor performance and further testing points to a bad sensor.

I prefer OEM parts and I have heard complaints of relatively short life on some aftermarket O2 sensors. for that reason, my recommendation is to use a genuine Toyota sensor, even if it costs more than an aftermarket one. When the aftermarket one is working properly, then functionally it is the same as an OEM one. If immediate cost is an issue, then an aftermarket sensor should work OK, at least for a while.

To expound on this a bit, the code you are getting only means the heating portion of the sensor has failed. If the sensor was not working, it can throw the computer into "limp mode" or it can simply misread the fuel mixture in the exhaust stream, and adjust the fuel in the intake incorrectly. If this happens, the fuel mixture can be too rich, meaning you consume more gas than you need to, and your fuel mileage will suffer as a result.

If the car made lots of short trips, then the sensor would be cold, and the mixture would probably be rich. If you started the car and made a long trip before shutting the motor off, then the mixture would probably be OK, but it would run rich early in the trip before the O2 sensor warmed up from the exhaust gas.

The heating element is part of the sensor, so the corrective action is to replace the sensor. The sensor screws into the exhaust system, much the same as a spark plug screws into the head. There is a special wrench to use that accomodates the wire in the sensor, but if your sensor is located in a spot with ample room, you can get it out with a standard end-wrench. The special wrench is a socket with a notch cut out so the wire doesn't get in the way.

I'm not so married to OEM parts for this application as Ray is. My theory is that exhaust gas isn't very complicated, and there are probably only three of four companies in the entire universe that actually make these things anyway. I wouldn't hesitate to use a Bosch or Autolite or other name-brand O2 sensor. I suppose Ray has a valid point though, Toyota can have higher quality standards for OEM parts than the aftermarket will demand. I am a skeptic, and I don't think that Toyota will have a different quality standard than the same part in the aftermarket. My guess is that Toyota uses a NGK O2 Sensor, but I don't know that to be a fact.

As Ray points out, the OEM part isn't going to cost substantially more, but it will offer a piece-of-mind quality that might be worth the cost.

A failed O2 sensor will not put the computer into "limp" mode. If the Electronic Control Unit ("ECU" detects a failed O2 sensor, it will illuminate the Malfunction Indicator Light (MIL), commonly referred to as a check engine light and go into open loop mode.

A malfunctioning O2 sensor or O2 sensor heater will not necessarily cause an overly rich mixture, whether the trip is long or short. All it does is keep the ECU in open loop longer.

For you, exhaust gas may not be complicated, but for automotive engineers, it is pretty complicated. If it were easy for automotive engineers, every vehicle would have nothing but C02 and H20 coming out the pipe a long time ago.

I wouldn't hesitate to use a Bosch or Autolite or other name-brand

A reason that O2 sensors deteriorate over time is that they are sticking into the exhaust stream, gradually getting coated with the crud in the exhaust. Enough crud builds up and the sensor can't sniff the O2 through the crud.

As far as the reliability of the OEM vs. aftermarket, I'm just going by my personal experience. On a friend's car, the original O2 sensor lasted around 100k miles, the 2 aftermarket replacements lasted about 50k each, or about half as long as the original one lasted. I have never replaced an O2 sensor in my personal vehicles so for me, the OEM O2 sensors have never failed.

I guess I'm saying that Open Loop and Limp Mode are the same. You are saying they are not.

I didn't mean it is easy, as in it can be solved. I meant it's easy in that all cars pretty much create the same gases that have to be analyzed and adjusted. O2 sensors all work pretty much the same way, kind of like light bulbs work the same way. They can work in varying ranges dependent on the environment, but once the range is determined, the rest is pretty much the same. There is little difference in a 15W light bulb and a 100W light bulb, once it is determined by the engineer that a 15W or a 100W bulb is needed, there isn't much difference in how the bulbs actually work. In that respect, it isn't very complicated.

Again, I respect that view. I don't share it, but I see how you arrive at it. I have only had one O2 sensor ever go bad, and the wires laid across the exhaust system and cooked. You are in the business, and have a much larger dataset to draw on.

Open loop is part of the normal operation of the vehicle, limp mode is not.

Under limp mode, the ECU fixes certain functions with no adjustment, like air/fuel mixture and ignition timing. The vehicle will run very roughly in limp mode.

I understood your original intent, sorry, I was just bustin' your chops! It's the Mr. Miyagi in me.

Some things to remember when working on Toyotas vs. German makes: - The Germans seems to do things the opposite of everyone else. Remember using a bolt to attach the wheels on a VW instead of studs and lug nuts like everyone else?

Before Mercedes Benz bowed to consumer demand and offered tilt steering wheels, their response when asked when they would offer one was "We spent millions determining the optimal steering wheel angle - why would you want to change it?"

Just remember Jeff-san:

Wax on, Wax off :-)

Could such a sensor be pulled from a junkyard car's exhaust system?

Lou

Yes, it could. There is no way to tell what the remaining life is. I'm not sure if the hassle is worth the cost savings.

I didn't know that distinction. I was thinking open loop and limp were essentially the same thing. Both would set the car to a setting that could get it home. What happens in open loop that is different than limp?

Sure, but why? The junk yard is where onen goes for hard to find stuff, and expensive stuff that seldom breaks and used parts will do the trick.

The O2 sensor is not expensive, it isn't hard to find, and a used one isn't going to be any better than the one you are taking off. The O2 sensor is a common consumable part, just like a spark plug, would you go to a junk yard for spark plugs? I wouldn't. It's much easier to get them from the auto parts store on the corner. Indeed, if I was going to get a used motor from the junk yard, I'd put a new O2 sensor in it just to be sure I didn't have to chase gremlins that came from the old one.

When an electronic fuel injection system is fully warmed up and operating at idle or partly open throttle conditions, it is functioning in closed loop mode. The O2 sensor is providing info on the amount of O2 in the exhaust gas so the ECU can adjust the air/fuel mixture accordingly.

ECU's will be in open loop mode when the engine is first started and the O2 sensor isn't heated enough, at wide open throttle to provide more enrichment, or if the O2 sensor is bad. Also, vehicles often run in open loop mode until the coolant temp come up a little. In open loop mode, the engine usually runs a little richer, resulting in poorer fuel economy. Heated O2 sensors help fuel economy and emissions by allowing the ECU to go to closed loop mode more quickly. So, a car can be in closed loop mode, and if the driver floors the throttle, the ECU will switch to open loop mode for maximum enrichment.

During open and closed loop mode, all the other sensors are still providing information to the ECU, like engine RPM, road speed, coolant temp, throttle position, EGR position, etc.

I have never encountered a vehicle in limp or fail-safe mode, but the check engine light usually flashes instead of comes on steadily to indicate limp mode. In limp mode, one or more of the circuits that the engine needs to even operate has a problem so the ECU uses pre-determined value, for example throttle position or engine RPM.

I knew all of that about Open Loop, I thought (rightly or wrongly) that limp was the same thing.

That is, I knew that closed loop required all of the various sensors, and open loop was when one of more sensor wasn't playing well with the others. I thought that was also known as limp. I wasn't aware that there was a difference.