I had a CEL thrown a few days ago, which I found to be a circuit malfunction on the rear O2 sensor.
I can't get the stupid thing to move. I've tried using PB Blaster when the thing is hot and wrenching it, same thing when it's cold. Should I take the converter completely off of the exhaust system so I can pick around the O2 socket if it's too rusted, or do some hot/cool down penetrating oil combination?

 

This is one of the most common misdiagnosed codes, most O2 codes that is, what was the problem and how did you verify it for the archives please. I dont hesitate to pull the convertor and carry it over to a shop with a fire wrench (torch), done. New gaskets too.

 

PB Blaster + let it soak?

 

Get the proper socket for O2 sensors at your local auto store.... it will work much easier!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Duane_in_Japan &raquo;</TD></TR><TR><TD CLASS="quote">This is one of the most common misdiagnosed codes, most O2 codes that is, what was the problem and how did you verify it for the archives please. I dont hesitate to pull the convertor and carry it over to a shop with a fire wrench (torch), done. New gaskets too.</TD></TR></TABLE>
Well, I was driving to work, and as the car was warming up the CEL came on and I noticed a loss of power. Later in the day the idle was poor and the CEL came on with a slight delay if I reset the computer after letting it sit for awhile, and didn't turn on if I just switched the thing on without actually cranking the engine (which verified it had to be something with the engine running). I hooked up the service connector and it blinks a code 65, which is for a circuit malfunction on the rear O2.

 

65, post O2 sensor heater circuit, this should have zero effect on drivability, you stated you had drivability issues. Yes, the heater circuit could very well be bad but I do not see how changing this part is going to help your root problem, did you ohm out the heater circuit cold and hot or check power to the heater. This sensor is only a cat monitor sensor, thats it.

 

I reset the computer with the cat hot (15 mile highway drive on an 80 degree day) and it still came on. Initially it came on after running in town and to the highway for about 10 minutes on a cool morning.
When the computer detects any problem with the O2 sensors, it keeps the car in open loop, which would give me off-normal engine behavior after the initial warm up. I managed to loosen and change out the sensor today and my CEL has stayed off. I reused the old wiring clip from the OE sensor so it's not a wiring problem, at least in that area.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Duane_in_Japan &raquo;</TD></TR><TR><TD CLASS="quote"> This sensor is only a cat monitor sensor, thats it.</TD></TR></TABLE>
Checks the primary sensor too.

 

Checks the primary sensor too, HOW, not by design of the entire system. YES, if the post O2 sensor was giving crosscounts then it would say that the primary sensor was giving crosscounts and that the primary is doing its job of controlling fuel delivery and that the cat was not working at this time, for what ever reason, more diagnosis to determine why, BUT the purpose of the post O2 by design is not to monitor the primary sensor.

IS IT theory that a non functional primary O2 sensor will put a vehicle back into open loop, I dont remember that one, open loop is a temperature related issue. I admit my memory is failing at the moment for an inop primary O2 putting a vehicle back into open loop, a post O2 going bad should AGAIN, have no effect on closed loop operation at all.

I have seen where some GM computers allowed the post O2 to effect fuel trims but they needed to be recalibrated (reflashed).

EDIT
I still find it hard to believe that a heater circuit code 65 will effect anything except the MIL, if the O2 gets hot on its own then the O2 will still work just fine and give no drivability issues. The heater was added to make the O2 sensor work quicker so it could clean up emissions quicker. Some sensors would go cold and stop working at idle, this is another reason for the heaters being installed, to clean up emissions at idle too. I am not arguing just by design and from reading thousands of posts I cannot see the post O2 effecting anything. If your car is truely fixed then great, can you please post back in several days to verify.

 

I am getting a heater sensor circuit malfunction on my code reader. How do the front and rear o2 sensors differentiate from each other and are they interchangeable?

 

I do believe they are the same and you want to be sure the good one is in the front. See my theory above.

I might concede that if the front sensor goes cold that the computer will enter open loop again but I do not believe that the rear will cause open loop operation.

 

It won't use the secondary sensor every day to check the primary. It's hard to put the diagram in my head into words... But if the ECM suspects the primary o2 sensor is acting up it can use the secondary o2 sensor reading to determine what the primary should be. This really only applies to OBD 2.2 Hondas

 

I have never heard of this in 13 years and as a member of the biggest professional website in the world, I have never seen it mentioned there either, nor in a dozen tech magazines, Honda is my strongest vehicle. Can you point me to something in print please.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Duane_in_Japan &raquo;</TD></TR><TR><TD CLASS="quote">I have never heard of this in 13 years and as a member of the biggest professional website in the world, I have never seen it mentioned there either, nor in a dozen tech magazines, Honda is my strongest vehicle. Can you point me to something in print please.</TD></TR></TABLE>
In my short time working at a dealer it has bitten me twice. A slight resistance problem in the secondary o2 sensor has caused a false code for the primary o2 sensor (a borderline faulty secondary o2 caused the ecm to code for the (good) primary o2). I've never seen it in print. One of my good friends in Honda training and I were discussing it and finally figured it out.
If you don't believe it, that's fine.

 

Above you stated that some sort of test is designed into the PCM for the post O2 to check the primary, I dont believe it, we are talking heater resistance, I will concede to a false code probability, although I do believe that many O2 sensor codes are in fact, not correct and need to be tested, I THINK that O2 codes are the number one misdiagnosed codes on the market. I respect your experience, just never seen it mentioned my friend, knowing that Honda is not greatly helpful with OBD anyways, remember they were forced to comply in the US market back in the day. They have one of the shortest lists of OBD enhanced codes available.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Duane_in_Japan &raquo;</TD></TR><TR><TD CLASS="quote">Above you stated that some sort of test is designed into the PCM for the post O2 to check the primary, I dont believe it, we are talking heater resistance, I will concede to a false code probability, although I do believe that many O2 sensor codes are in fact, not correct and need to be tested, I THINK that O2 codes are the number one misdiagnosed codes on the market. I respect your experience, just never seen it mentioned my friend, knowing that Honda is not greatly helpful with OBD anyways, remember they were forced to comply in the US market back in the day. They have one of the shortest lists of OBD enhanced codes available.</TD></TR></TABLE>
If Honda can't explain their DVD player to me I surely don't expect them to be able to explain an ECM.

 

Well, I've driven on cold mornings straight out on the highway like when the MIL was first thrown, hot days, all day, highway, in-town downtown, whatever, and the MIL has stayed off. All I replaced was the rear O2 sensor, again, I reused the original harness. Based off of all of this, it seems problem was the rear O2 sensor, and I'm really not sure why that's still being contested here.

 

Thanks for the verification, I will remember this one as par for the course.

 

I'm only asking because I have a rear sensor circuit malfunction on the secondary o2 sensor. I have a second engine in my garage that has a good o2 sensor on the front. I was wondering if I can pull the good one out of the other engine, cut the harnesses and wire in the good o2 sensor in place of the bad one and turn off my CEL.

 

the o2 in the front is diff., than the rear, just cause u have an o2 code, doesnt mean the o2 is bad, check possible causes for that code such as cat efficintcy, lean/rich af mixture.