Rep Power: 0

Ok so I recently bought a 2001 Civic gx which from the factory runs on natural gas. It was an ex-government vehicle. The car runs great. it has about 115k miles. it has an automatic tranny. So i went to get an inspection thinking it would pass no problem. NOPE. Turns out when they hooked it up to the computer there was 5 codes going off. p0300 which is random cylinder misfire as well as individual misfires in each cylinder. The car does not have a misfire.... and weird part is i didnt notice the codes because the CEL isnt on! so i thought i had a bad bulb in the CEL. replace it. still no light. light does not cycle on when you first turn the key. and when i hooked my scanner to it, sure enough the 5 codes were there. and the scanner says CEL status: OFF.....
Anyone have problems with this before? I changed spark plugs all are very clean, no oil. changed battery. took off and cleaned the grounds I could see. I need some guidance as to the next step i should take.... Im leaning towards the idea that the computer is messing up. any help is appreciated! thanks

 
Rep Power: 517

So..... the code is no longer active, the codes are now history codes.
It takes 3 'good trips' to turn off the CEL, but the data is stored in memory for a much longer period of time.

Got freeze frame data? Post it.
What are all of the codes?

You say it is NOT misfiring, and the CEL OFF status agrees with this.

Clear the codes and drive it until the monitors have passed.
Recheck for any codes before you head to the inspection place.
See if your area wants all of the monitors to have passed or if you can have 1 or 2 incomplete and still pass the test.


The inspectors should have checked for the CEL coming on when you first turn the key on (bulb check), so if you don't fix that then you can expect a fail for that too. (MOST places expect that light to work)

Follow a wiring diagram and see if you can make the CEL bulb work from the computers plug. Maybe someone cut the wire or something so the light wouldn't be seen (so you would buy the car?).


tl;dr
Clear codes and fix the light.
Drive it and see if codes come back.

 
Rep Power: 0

i have now cleared the codes several times and driven over 400 miles but still they keep coming on. they are p0300 0301 0302 0303 0304. i dont think the government agency would go as far as disabling the check engine light. it was a "no inspection" auction anyway meaning i couldnt look at the car before i bought it.
even after the codes are cleared, when they eventually come back the CEL status is still OFF....

 
Rep Power: 0

oh and the only way to pass here is to have no codes at all.

 
Rep Power: 517

I'm sorry, I don't think I have any good answer for you.

Even though I have taken all of the CNG vehicle training available from Honda, we have no CNG cars in my area so I have no real world experience with them.

If you had some freeze frame data (that should be stored along with the code), that would let you know some of the running conditions that were happening at the time the code(s) set. That might aid in the diagnosis to some extent.




You might do some basic routine maintenance checks, like valve adjustment....and see if the cam and crank (timing belt) is timed correctly...

Then do a compression test?