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96 Honda Civic EX 130,000 miles, D16Y8 engine, automatic.

It had a CEL and when I pulled the code it pointed to a pre-cat O2 sensor heater. Replaced the sensor with a brand new Bosch 13007 and the CEL went out right away. Fuel economy was the same before and after the new O2 sensor.

Need to pass smog, but two inspection monitors (cat, and O2 sensor) do not pass. I have been driving it from cold for several days now, and the smog shop just told me yet again that those two have not passed yet. I have driven it for 360 miles since precat O2 sensor was replaced.

I found a couple of online lists of the driving cycle to follow and I have done that, but in order to do so around here, I get up very early in the morning when the freeways are empty.

I am stumped, but several shops and smog stations I went to tell me that many cars are running into this problem, and there is not much to be done. The last smog station I went to tells me that maybe the post-cat sensor voltage is at 0.95 rather than 0.45V (he checked the coolant temp it was 95C/202F so it was up to temp), and that it might be the post-cat sensor, or the cat itself, or perhaps there is an exhaust leak. He tells me to keep driving it for a good half hour at a steady 55 etc. But there are no DTCs, and the CEL is not on. He said that it may be possible for no DTCs to set for a marginal post-cat sensor. He said if all else fails, I can bring it in for a 1hr diagnosis ($90) which will include putting it on the dyno which will guide the process and possibly point to what is causing the issue. (This sounded a big vague, but the guy seemed fairly decent and not out to get me).

He also said I can try to use some 'CRC guaranteed to pass' fuel tank magical fluid that might help. He did say that he was just as skeptical of that but saw it work on a few cars.

Here in California, all I/M need to pass, otherwise the smog check fails.

I am planning on changing the post-cat sensor (Amazon and Bosch tell me the same 13007 one is used for pre- and -post). It's not my style to throw parts without diagnosis, but how do I diagnose the post-cat sensor?

What's the best course of action here?

 
Rep Power: 518

Did you ever ERASE that code from the computers memory?
Is there still a (history) fault code stored for the sensor?

*COUGH*crap*COUGH*

I'd first throw away the bosch sensor (or trade it for) and install an NTK or DENSO sensor. If you still have the original sensor, wire brush the crud off and see what brand it was and stick with the same brand.


Do you have your own code reader that can show you if the readiness monitors have completed?
At the end of a test drive, did the monitors complete?
Do they go back to incomplete after cycling the key off? Do ALL monitors go back to incomplete?

Got a scanner or anything that can display live operating data from the ECM? What do the O2 values look like as you drive around?


How many monitors can be incomplete at the time of emissions testing and still be accepted for testing? One incomplete according to Calif. rules.
http://asktheref.org/About/MonitorReadinessConcerns/tabid/552/Default.aspx


Sadly, I didn't find factory info on the preferred OBD drive cycle for a 96 in the 3 minutes I was looking.

 
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The original is Denso 234000-2311, which I am guessing is really 234-2311 ?

https://www.amazon.com/Carrep-Oxygen...so+234000-2311

I found only one source for this through Amazon, but it's made by some obscure brand, not denso.

Denso's website says the correct upstream one is 234-4099. Should I try 4099 or 2311?

No, it is those two that don't complete at the end of a drive. They don't all go back to incomplete. I checked all that just in case there was some electrical issue that disconnects/resets the ecu at the start/end of every drive cycle.

If you have any info on any honda drive cycle, pass it along. Even if it isn't the one for my model it will give me some ideas on what else to try. Here is the one I have been using, but I believe it is a generic drive cycle to set readiness, so it may not be all that useful for Hondas. I'll try to check with a referee center to see if they can give me a specific one.

1. As soon as the engine starts, idle the engine in drive for two and a half minutes with the A/C and rear defrost on. (OBDII checks oxygen sensor heater circuits, air pump and EVAP purge.)

2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle. (OBDII checks for ignition misfire, fuel trim and canister purge. )

3. Hold at a steady state speed of 55 mph for three minutes. (OBDII monitors EGR, air pump, O2 sensors and canister purge. )

4. Decelerate (coast down) to 20 mph without braking or depressing the clutch. (OBDII checks EGR and purge functions.)

5. Accelerate back to 55 to 60 mph at half throttle. (OBDII checks misfire, fuel trim and purge again.)

6. Hold at a steady speed of 55 to 60 mph for five minutes. (OBDII monitors catalytic converter efficiency, misfire, EGR, fuel trim, oxygen sensors and purge functions.)

7. Decelerate (coast down) to a stop without braking. (OBDII makes a final check of EGR and canister purge.)

 
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One more question on the old primary sensor. can I use a resistor across the heater pins to see if that will let the ECU set IM readiness?

I really hate those kinds of hacks, but until the new sensor arrives I am trying to use this downtime to do some troubleshooting.

Also, is it safe to back-probe the oxygen sensors with a multimeter while they are connected to the ECU to check voltage?

I want to make sure I don't set any more DTCs, or reset the ECU and wiping out the other readiness monitors.

Also, on the scan tool question. I had bought one that was highly rated, but it had some issues (and on several cars) so I had to return it - I can't find a link to it, but it was a straight up scanner with cable and a few buttons. Is there one anyone would recommend that would let me look at readiness monitors, and DTCs? I've spent many hours reading reviews and I am not the wiser. I have an android phone with bluetooth and can install the torque app, etc.

 
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I did not erase the fault code with a scan tool, because I didn't want to reset all the readiness monitors.

The smog shop that scanned it with their professional scanner didn't see any stored codes. I've had it scanned by a shop several times now and no-one said there are stored codes. I saw the screen on a few of those scanners display 'No DTCs'.

 
Rep Power: 518

Obscure????
Denso the brand, isn't made by anyone else.

I looked up a 96 Civic EX 4-door, auto trans with California emissions (If this isn't an exact match to your actual car, the sensor number I found may not be right)

In a Honda parts catalog I came up with Honda part
number 36531-P2R-A01 for the upstream O2 sensor.

I looked up the DENSO cross reference chart for these sensors: http://www.impocali.com/images/pdf/C..._Reference.pdf

Cross the Honda number in the chart (page 467) and it shows Denso part #234-4099

I can't say the Bosch sensor is your entire problem, but I do know many of the cars don't like them. The cars tend to work best with original brand parts.
As stated in the previous reply, I don't have that info and couldn't find anything relevant in my info.
I don't live in an area that has emissions testing, so I really don't ever have to deal with this stuff. PTL


Try leaving all those electrical consumers OFF.

Also, I sent you a PM.
No.
Wait wait...what do you hope to accomplish by doing this? What sort of theory do you have?

What codes did it have that caused you to replace the sensor in the first place?


If you already know what backprobing is and can do it, you're probably miles ahead of most other posters LOL.
Sure. Try to avoid damaging the insulation and connector seals, you want to keep the wiring waterproof.

At this point, who cares? You're gonna need to keep driving to get at least one of the last two monitors to pass, that's gonna take miles.
The O2 monitor probably has to run and pass before the cat monitor can begin.
No scanner opinions from me. I have access to dealer level equipment.


So it's been working long enough for the PCM to purge that stored info. Good enough.
I had the thought that maybe a stored history code could prevent the monitor from running.

 
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Well, the Denso sensor arrived last night, I installed it this morning and went for a drive with an obd2 scanner plugged in. Low and behold, it set the o2 sensor monitor within a couple of minutes of hwy driving, and about 15 miles later, it set the cat monitor.

Later in the afternoon after the car was driven on a couple of in-town trips, I checked again, and those two readiness monitors were showing incomplete again -- all the other ones were showing complete. No DTCs.

What on earth is going on? I thought those two monitors are not the continuous type and are run periodically. What else could be going on?

I don't have any evidence of electrical issues. Car cranks and starts with no hesitation, and the other three readiness monitors persist.

I'll try to see if I can read the fuel trims, and go for another drive to see if I can set them all again.

The Denso came in a box marked 234-4099 but the sensor itself had different markings:
Denso
41300
03T29
I will call them up on monday to find out what those markings mean.

I am turning gray trying to get this ready for the smog check. And let's hope it stays below the 487 PPM NO threshold. It was just under that the last couple of times.

 
Rep Power: 518

Now you KNOW it's at least possible to pass.
Just drive that same pattern to get the monitors to set then head for the test station.

The O2 monitor might reset after each key cycle, and the monitor runs during every drive cycle?
I really don't have an answer, and like I said I don't have to deal with emissions tests in my corner of the planet.

You ought to find an identical car and plug the reader in to see if it also resets those monitors after a key cycle.

I wouldn't bother with that. Manufacturers markings aren't the same as part numbers. Those could indicate production line, processes, mold numbers, time and date, shift, etc.

The sensor WILL pass the monitor now, you already saw it happen. The sensor is no longer questionable.

 
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It passed smog with flying colors actually (in fact, 0 PPM NO, unusual for this car).

The problem is that it does not persist readiness for 3 monitors. The O2 heater monitor is set within 5 seconds of a start, the O2 monitor is set within 1.5 miles or so of highway driving, and the cat can take anywhere from 15-40 miles on the highway (maybe longer?).

I don't know yet if it resets fuel trims each time.

In all the years it had to pass smog, it never needed to have its readiness set. It never goes on the highway unless I do it, and there have been battery disconnects at various times.

e-zone, can you think of anything that might be causing this? ECUs are supposed to be very robust and reliable, so I am inclined to think the ECU has a valid reason to reset those two readiness monitors only.

There are no exhaust leaks.

 
Rep Power: 518

A pass is a pass, yes?

Is it over now?
Or are you still needing to get monitors to complete before you can test?

Three monitors now? I thought you only had 2 that wouldn't set before?



I don't have a car that year-- or any 6th generation Civic-- to double check on, and like I said earlier I don't have to deal with emissions testing in my area.

Weak battery, causing a ECM reset during starter cranking because voltage drops below some memory dump threshold??

 
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To clarify, yes, it passed. No more long drives to get the car ready for the smog dyno.

I'll dig more deeply into this. Thank you. I was hoping the ECU would help out here by logging a power drop DTC, but that wouldn't be very exciting, now would it?

 
Rep Power: 518

The ECM was never programmed to detect any such faults, so you'd never find a code for a weak battery. Most people would notice slow cranking when the battery gets weak.

The ECM grounds (the clump of wires on the thermostat housing) might be affected by corrosion/poor contact/elevated resistance, during the high amp loads of cranking too.


Another thought, that ECM is probably 20 years old now, and some were susceptible to leaking capacitors causing weird electronic actions and sometimes circuit board damage.

 
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Thanks ezone. I really appreciate any ideas on this.

I've had to repair even brand-new electronics that had leaky caps, so I am familiar with the kind of repair involved.