[WhyHonda]

My check engine light has been on and off for awhile and at first there is only one code (P0420). And since it didn't' affect performance of the car, I didn't pay too much attention to it.

Now my check engine light is on again and it stays on for almost a month. I know there must be some more serious problems and have the code scanned again. This time I found four codes (P0420 appears twice):

P1167 Air/Fuel Ratio (A/F) Sensor (Sensor 1) Heater System Malfunction
P1162 Air/Fuel Ratio (A/F) Sensor (Sensor 1) Slow Response
P0420 Catalyst System Efficiency Below Threshold

It looks like I have a bad A/F sensor heater (P1167) and because of this, the sensor has slow response (P1162). I searched this forum and didn't find any posting about these two codes. Could anybody tell me what is the problem or at least where is this sensor/heater?

The two P0420s probably mean I have both catalyst converters failed. I will try to correct them after I fix the more serious problem.

Please help me!

 

[Yves M.]

P1162-67 They point to either the ECM is bad or the Primary Oxygen sensor is bad. There is no heater anywhere. It is the Oxygen sensor.

P0420 says the TWC (Three Way Catalytic) converter is bad. The secondary oxygen sensor reads the output of the converter and seems to report that the converter is not 'converting' enough.

Maybe the bad O2 sensor broke the catalytic converter. I dought that it is the ECM (but it is possible)

Am I correct into thinking that you drive with high MPG and you get lean burn often.

 

[Insightful Trekker]

The primary O2 sensor heater is bad. All OBDII cars use heated O2 sensors to bring them up to operating temp faster. The O2 sensor is the primary input sensor for "tuning" the air fuel mixture. Without its input the PCM can only take its best guess at controlling the mixture. Read: expect much lower MPG especially with an Insight.

You'll need a new one and its not a common variety.

See:
http://www.insightcentral.net/forum/vie ... 27d05ffae8

Mixture control is also important to prevent CAT (catalyst) damage although I don't believe that a "cold" O2 sensor of and by itself can achieve this.

HTH!

 

[Yves M.]

Sorry, I see I was not clear. There is no external heater.

The actual physical auto part is 'the' oxygen sensor. As an integral part of the sensor, there is a heater within. One can not replace the heater alone to my knowledge, the sensor needs replacement.

 

[WhyHonda]

Thanks guys for all your input! Looks like the common diagnosis is the main O2 sensor (the one located in front manifold/exhaust pipe before catalyst, 5 wires) is bad. I will try to buy one and replace it.

Do you know any source I can buy it cheap? I found one on OxygenSensor.com and it costs almost $290. Compare to the $50 one on my Ford, it's too much. I don't know if it's worth the money or it's just price control by Honda?

I will let you know the result.

Thanks again.

 

[WhyHonda]

I forgot to mention the ECM in my car is still the original and not the new one from the recall. So if I replace it with the new one, all the problems may go away?

I have about 120K miles on it and an average of 62.9MPG. I use lean burn a lot on highway driving.

Thanks!

 

[JLR]

Some of the replies you have gotten so far are inaccurate or misleading, although I'm sure they were well-intentioned. A P0420 does NOT mean the catalyst has failed; it only means that it is (as the code description says) inefficient. True, many P0420 codes turn out to be caused by a dead cat (mine went at 79,850 miles), but your other codes suggest that the cat is only temporarily inefficient. No catalyst can operate efficiently when an oxygen sensor's performance is degraded.

Your P1167 and P1162 codes do not refer to an oxygen sensor; they are for (again, trust the code descriptions) your air/fuel sensor. A/F sensors are very different from oxygen sensors. Your Insight needs an A/F sensor to achieve its superlean mixtures; an oxygen sensor could not keep up (by the way, oxygen sensors do not measure oxygen, but that's a subject for another time). Yes, A/F sensors really are that expensive. No, you don't want to find a bargain replacement.

You are probably correct in your guess that a failing A/F heater, which is part of the A/F sensor, caused the A/F sensor to have a slow response. The heater is the weakest part of this sensor. Whether or not your cat is damaged will depend on how long you drove after a P0420 was recorded by your ECM.

Once you have replaced your A/F sensor, it may take up to 100 freeway miles before your catalyst cleans itself of carbon deposits. If the P0420 persists AFTER that time, then the cat may in fact be damaged.

Your ECM would not have caused this; the reason they were recalled is a calibration issue unrelated to this problem. Good luck!

 

[Insightful Trekker]

<snip>

Your P1167 and P1162 codes do not refer to an oxygen sensor;...

<snip>

A P0420 does NOT mean the catalyst has failed; it only means that it is (as the code description says) inefficient.

Insight factory SM pg. 11-7, P1162, "Primary Heated Oxygen Sensor (PHO2S Sensor 1) Circuit Malfunction." And P1167, "Primary Heated Oxygen Sensor (PHO2S Sensor 1) Heater System Malfunction."

Yup, could be an open/short circuit failure on this branch or PCM failure.




Good point. Push a "good" CAT hard enough and it will code.

The Sensor in which you refer to as the A/F sensor is more technically an LAF type O2 sensor, which is an uncommon variety. Page 11-25 and various scattered places in section 11 of the factory SM. You just have to "know" that a 5 (+2 heater) terminal O2 sensor is of the LAF type (Linear Air/Fuel).

However, if the primary code is a P0420 (especially if its the only code with no other driveability symptoms) then its overwhelming likely that the CAT is bad. Inefficient = insufficient performance to do its job = replacement needed = bad.

Since the OP wasn't concerned about initially replacing the CAT I saved my fingers the wear for later. <g>


DIY diagnosis of automotive problems has been around for many years, and will continue. Even with the very complex circuits that most new cars now commonly use. More often that not the DIY'ers get lucky with the throw a part at the problem type repair. But with the increasing complexity and cost the odds of success are narrowing.

The philosophy of pinch a penny now only to have to spend a dollar later to fix it right the second time is increasing.

"Feeding" didn't used to be much of an issue either, until the Insight. Look at the number of posts and inferences in regard to "poor" (50-60) MPG. <VBG>

HTH!

 

[Yves M.]

Thaks for the input messages above.

I just checked the Service Manual and the Pcodes list I have on my site:

The service manual does list the codes to the "Primary Heated Oxygen Sensor " which is good

The list I have on my site, list the code to be the "Air/Fuel Ratio Sensor" , which seems bad.

Now I did not verify all the codes in the list on my site. It came from an Honda site. The code description in not very good. I will check them up with the manual (not all are listed but most Insight related are) to change the descriptions

I do not know what an air/fuel ratio sensor is. To me, the only solution was the Oxygen sensor. It is the only sensor that reads the fuel mixture. Now please correct me if I am wrong.

I know of an air mass sensor, intake air temp sensor IAT, manifold absolute pressure MAP,... but only the exhaust has an ratio sensor (oxygen sensor). No?

 

[bretthans]

As others have mentioned, you may want to check the wiring before springing for a new LAF sensor. A bad ground or heater wire would cause a malfunction. It's tough to find all the problems with a wire harness, but I would check the most obvious, such as at the sensor connector. The heater is an integral part of the sensor, but it will likely have two wires dedicated to it. If it fails (or is disconnected), that could easily cause the other codes you are seeing.

For anyone interested, the heater is required to make the A/F sensor into a LAF (linear air/fuel) sensor. The sensor is very non-linear unless the temperature is closely controlled. Keeping the sensor in a linear range allows for better control of the mixture. Outside that range the ECM will do a rough approximation.

 

[WhyHonda]

Thank you guys for all your inputs!

After reading all your postings, I still have one more question: The heater inside the O2 sensor should be for cold weather only. If the weather is as hot as Houston, Texas here (still in 90s during the day!), you really don't need a heater. And I believe this code appears during this summer. Which makes it very unlikely.

So I think what happened is either the wire is broken or poor connection, or the heater is broken. When the computer senses this, it will turn on the "slow" code automatically.

This weekend I will use a resistor to cross that two heater wires to trick the computer think there is still a heater. Then I will clear all the codes and drive for awhile, see what will happen.

I will let your guys posted.

 

[Insightful Trekker]

This weekend I will use a resistor to cross that two heater wires to trick the computer think there is still a heater. Then I will clear all the codes and drive for awhile, see what will happen.

BAD mistake. Get the current flow too high and you can "smoke" the PCM ($$$).

The heater is _required_ for correct O2 sensor operation. If the heater side of the circuit isn't open or shorted, you need a new sensor. There's no other way. And the possibility exists for CAT damage _IF_ the O2 sensor inputs get too out of range. Much bigger bucks ($) for those parts.

HTH!

 

[WhyHonda]

I just disconnected that O2 sensor and measured the resistance between the heater, it's about 3 ohms. Since I can't measure any resistance between any other two wires, I assume it's the heater. It's between the blue and yellow wire.

Since I still have resistance, the heater is not broken. So loose connection/bad wire must be the problem. I cleared the codes and verified they are all gone for now.

By the way, if the heater were broken and I used a 3 ohms resistor to cross the heater wires, the computer won't be able to tell any difference because a resistor is a heater itself. If I used a resistor too small to generate too much current, I believe there should be a fuse to cut it off. And a bigger resistor won't cause any problem either because now the whole thing is under current.

I will let your guys know the final result Monday when I drive it to work.

Thanks!

 

[Shotster]

Yeah, me too!

I just bought a used 2001 Insight a few weeks ago, and the check engine light is on most of the time as of recently. I took it to Auto Zone and got P1164 and P0420 codes.

P1162-67 They point to either the ECM is bad or the Primary Oxygen sensor is bad. There is no heater anywhere. It is the Oxygen sensor.

So does P1164 mean the same thing? It wasn't even in the system at Auto Zone when the guy looked it up.

P0420 says the TWC (Three Way Catalytic) converter is bad.

Yipes, that sounds expensive. Where exactly is that? Is it the thing under the car toward the front that looks like a muffler, or are we talking about something else entirely? :shock:

 

[Shotster]

How do you "clear the codes"?

I cleared the codes and verified they are all gone for now.

I've been following this thread because I am currently experiencing a very similar problem, except that I'm getting a P1164 along with the P0420. I have a couple questions:

1) How would I go about clearing the diagnostic codes?
2) Is the "main" sensor the top one on the exhaust pipe just behind the engine? It has 5 wires. I see another sensor just below it (and also on the pipe) which appears to have 4 wires. Does the P1164 point to one of these sensors?

Also, is it best not to drive the vehicle until the problem is fixed? I just bought this Insight (a 2001 sith 72K miles on it), so I'm rather new to things. Thanks for the help.

---
Steve

 

[Shotster]

Ok, I'm doing some sleuthing and learning fast. The sensor that's higher on the pipe is the LAF, and the lower one is the O2 sensor. Here's my next question... The description on the Auto Zone computer for OBD-II DTC P0420 was "Catalyst system efficiency below threshold (bank 1)". My question is, what's the "bank 1" mean?

Thanks for the help,
---
Steve

 

[Insightful Trekker]

<snip>

My question is, what's the "bank 1" mean?

Thanks for the help,
---
Steve

In a multi-banked system (with Honda it means either a I4 or v6 engine. Each cylinder "bank" is monitored by an individual O2 sensor. Bank 1 is always the bank related to the #1 cylinder.

Some other makes and models are setup with 4 O2 sensors 2 ea. per bank with one CAT per bank. Therefore each bank requires 2 O2 sensors one above each CAT and one below.

HTH!

 

[Shotster]

Thanks for the reply, John. So then, a bank is a group of cylinders and not a single cylinder, right? Since the Insight has only three cylinders, does that mean there's only 1 bank - i.e. the group of 3 cylinders? And thus the 420 code is referring to the catalyst that's just below the LAF sensor?

Thanks for the clarification.

 

[Insightful Trekker]

You are correct Shotster.

I oopsed in my eariler post and forgot to include the Insights I3 (I=Inline) configuration, sorry.

OBDII codes by law must be transportable across all manufacturers. Not all cars will share all codes but the same code on 2 different cars must be the same symptom.

btw The LAF sensor is a specific type of O2 sensor. And is commonly called such. AFAIK LAF type O2 sensors are not used as a secondary O2 sensors. Their type of output is not necessary for its function in that location. And I believe that only "lean burn" Honda models use this type of O2 Sensor ( Civic VX (early 90's model?), Civic HX 98-00, Civic Hybrid and the Insight). A LAF type sensor gives accurate readings well beyond what a mere mortal O2 sensor is capeable of and is necessary for the "lean burn" range of operation.

I sincerely hope that WhyHonda dosen't end up causing secondary damage. Instead of trying to write an encyclopedia on the topic I've kept it simple. He's wayyyy out on a limb with his "bypass" approach and is risking big bucks damage. Time will tell and ultimately only he will know for sure.

HTH!

 

[Shotster]

One last boneheaded question...

Assuming the DTC correctly identifies the problem, then if the problem is fixed (e.g. a sensor is replaced), does the trouble code automatically clear (and thus the MIL automatically go out), or must the diagnostic code be explicitly cleared somehow?