OBD Emissions Readiness Monitors Resetting on Shutdown

[00scrub]

Hi, I'm running into a problem on a 10th Gen Honda Civic. All the emissions monitors show not ready. We've gotten them ready and as soon as we turn the car off they jump back to not ready. Anyone seen this before?
We've checked the #7 "Meter" Fuse in the interior fuse box and it has continuity. It gets voltage when the car is running and has no voltage when the car is shut off. Is this normal behavior?
Thanks

 

[CleanSump]

You can erase the codes, but the engine has to be put through a number of driving cycles before it will show "ready" for an emissions test. It's to keep cheaters from clearing codes and driving straight to the emissions inspection.

 

[00scrub]

Hi @CleanSump there are no codes and we aren't clearing anything with the reader. We are just monitoring the status of the Emissions readiness statuses after a drive cycle (EVAP, lambda heat, EGR, etc).

 

[Eddie Hudson]

Check your battery cables. They might not be making a secure connection.

 

[SC Maintenance]

Sounds like maybe the memory is faulty and it looses that when the ECU goes to sleep. You would need to find someone more knowledgeable on that particular ECU. Depending on how new I would expect its flash or something.

 

[Mechanician]

Check the Engine ECU fuse under the hood.

 

[Mechanician]

From what I can see online it's #12

 

[mk378]

The fuse that supplies constant memory power to the ECU used to be called "BACK UP" but that was many generations ago. What model year do you have?

 

[00scrub]

Hi thanks. I'll check that fuse.
It's a 2018 Civic Type-R. Is that still the same fuse number?

 

[mk378]

Yes fuse 12 in underhood box, 10 amp circuit hot at all times.

 

[Marcozi]

Hmmm, I thought engine computer memory was non-volatile.

 

[mk378]

Hmmm, I thought engine computer memory was non-volatile.

That is more and more the case, but some PCMs still store temporary data like fuel trim calibration and OBD codes in RAM which is backed up by a "hot at all times" circuit from the car battery.

 

[Mechanician]

That is more and more the case, but some PCMs still store temporary data like fuel trim calibration and OBD codes in RAM which is backed up by a "hot at all times" circuit from the car battery.

I've never seen an explanation of the engineers' reasoning on why some things are volatile, and other things are not.

I do remember in the early 2000s VWs had problems after a low battery - attempted start. The low voltages would cause the "basic settings" to go all out of calibration. Often the car would have to be towed to somebody with a scan tool to reset everything after a new battery was installed. That may be a good valid reason to let some stuff get wiped after a loss of power.

 

[00scrub]

Hmm fuse 12 in the CTR is fi-ecu. It is measuring 0V off.
I just checked the LAF fuse (fuse 11) and it has 12V on it even with the car off and door locked. Is this normal behavior?
I checked the Back up fuse (fuse 18) and it is 0V with the car off and locked

Turns out the car also has an Igla anti-theft installed. Not sure how that exactly works, but I wonder if it could be interfering.

 

[Mechanician]

As stated above that fuse should have constant power. Good noticing that aftermarket item, I would bet the anti-theft is the culprit.

 

[Chris142]

Turns out the car also has an Igla anti-theft installed. Not sure how that exactly works, but I wonder if it could be interfering.

That is most likely your problem. Incorrect instalation.

 

[Marcozi]

That is more and more the case, but some PCMs still store temporary data like fuel trim calibration and OBD codes in RAM which is backed up by a "hot at all times" circuit from the car battery.

Thanks for the information.

 

[mk378]

12 in the CTR is fi-ecu

By "CTR" you mean the fuse box under the hood?

I think most of the small fuses are powered through one of the sections of the multi-element main fuses that bolt into the box, but the diagram I have does not show exactly how.

An alarm install should not involve the fuse 12 circuit which appears to be wired only to the PCM, but who knows what the installer actually did.

 

[00scrub]

Hi CTR = Civic Type-R.
It shouldn't but this alarm somehow shuts the engine off if a code isn't entered before a set time. I'm not sure how it's wired up and will be taking it to the installer next week to have them take a look.
What else could effect the 12V on the Back Up fuse? Could a bad/damaged PCM/ECU or relay impact this?
This is what the underhood fuse box diagram shows for us:

 

[Mechanician]

There are 4 block (main) fuses in that fuse box, one of the links inside one of them feeds the #12 fuse.
It's possible that link is blown, but usually there are other circuits that would be affected causing more problems with other items.
I don't have access to a power flow diagram to tell you where to look, or which one it is.
They look like this so you would be able to see inside it. And see if a link is broken / blown when you remove them.