Okay, so this might not be new to you... But I just found these out...

If you clear your CEL, you'll have to drive around for 50 miles before your car can go through the smog check.

If you get a CEL, say a P0304 misfire on cylinder 4. It'll go away after 20 restart without another misfire. Go away as in out of the ECU and light off.

So if you have to get your car smogged but you know the CEL will come back within 50 miles but long enough to get through the smog process. Get close to the smog station, restart 20 times (not sure how bad this can be to the car if you restart back to back 20 times), and get the car smog...

I was getting a bit nervous because my car needs to be smogged next month and I had a P0304. But after driving a while with the Lucas Fuel Treatment the light went away by itself. I thought the light was off but the code still in the ECU. So I went to autozone to borrow the OBDII, that's when I found out about that 20 cycle thing. My CEL went away on its own, and I hope it doesn't come back...

Just FYI...

 

I think most of what you're saying is true, I hadn't heard about the 20 cycle thing though. That might not apply to stuff like having a cel for a bad o2 sensor though or a 'altered' o2 sensor. There are a bunch of sensors that need to complete a cycle to gain "ready" status. So even if you reset the ecu and have no cel when you roll in for smog they can still fail you since there will be no readings from certian sensors because their computer will show them as not having completed the monitor cycle. I guess thats why you need to drive 50 miles before smogging after a reset, unless something is still wrong then the cel will pop back up again.

 

stg2lgcy00 has it right - it has more to do with individual sensors starting and gathering enough data to start reporting correctly rather than starting the car a certain amount of times or driving a certain distance.

 

it'll be fun when i get mine tested next year. can i just clear the CEL (po302 and po304) before i go to get it tested for smogcheck?

 

No, that is what this whole post is about - the fact that you CANNOT simply clear your CEL, turn up at a shop, and pass.

Dude - pick up that stock flywheel I PM'd you about! It could be all that's still wrong. Is it still showing a CEL??? I thought it was done with that nonsense.

 

Thats what the OB2 interface part of the smog test is about.
You can't have more then 2 OB2 monitors incomplete or pending in order to pass the smog test.

Back in the olden days dealers and shaddy people would turn off the MIL and smog the car and then later on the light would come on.

Just think if you were one of the people that bought a used car, drove it home and had the light come on saying your transmission is starting to slip 4 days later

When you clear the ECM, you have to perform certain "drive cycles" for the computer to perform a self test of said systems and OK the monitor.
Some cars this requires 50-100 miles of driving (Volvo,Nissan) and letting the car heat cycle, some cars it requires 10 miles and no heat cycling.

Regards

 

send the dude a pm. let's see if he ever gets back to me.

yup, still showing a cel. i just drive it with the CEL on.......

 

It's all about the readiness monitors for the smog check (as well as the CEL being off, of course).

Something to consider though for those with "more modded" cars....the readiness monitors might be able to be hacked. I know that is certainly the case on my Impala with the OBD-II ECU (96 Impala only, 94-95 were OBD-I and thus are trivial to make pass). With some "creative" programming, you can make it up so that as soon as the ECU is plugged in and powered up, ALL of the readiness monitors INSTANTLY show up as "ready" to a scan . You still have to pass tailpipe and visual (as well as CEL off) of course, but it does mean one less PITA thing to deal with at smog time.

Not sure if the same can be done yet on a Subaru ECU, but I wouldn't be shocked if it can be done...someone more familiar with OpenECU or StreetTuner can probably comment more.

 

i don't know if this would help, but when i had to smog my car in 2006 i was having a knock sensor code that triggered the CEL. i was visiting my friend at the shop he was working at, and when i started my car to leave the CEL was gone. so i decided that i better get it SMOG right away since the CEL was gone. smogged it, passed. CEL came back later on that day.

 

P0304 was what my car always threw for about a year- before the motor burnt.

Just don't disregard them, especially if it starts happening a lot.

 

****.....yea my misfire cel keeps comin up and its in like 3 cylinders