"check engine" light

[tmleadr03]

Did they just recently change the emission law that you CAN have a check engine light, or that you can not? I remember it used to be that as long as you passed, it didn't matter if a light was on or not.

I have had customers make it through with a check engine light, but not with a check engine and a ABS warning light. Have to have the ABS light off before it gets on the dyno.

[tmleadr03]

On the newer ones you need to turn the lights on and try to start it with the battery disconnected or wait a really long time to fully drain the system. Otherwise it'll hold the information. Also car may run rough for a minute or gas mileage drop for a short time when it restarts after this as the computer needs to relearn what setting it had before.

OBD scanners are so cheap now that it's almost pointless to not have one though, and then you can reset it yourself w/o all the hassle.

I have had cars come in with codes, disconnected the battery started taking stuff apart, waited on parts and days later got the vehicle back together and the codes were still in the system.

If you turn off your PC computer do you lose all the information stored on it?

[BigNick73]

I have had cars come in with codes, disconnected the battery started taking stuff apart, waited on parts and days later got the vehicle back together and the codes were still in the system.

If you turn off your PC computer do you lose all the information stored on it?

Well I'm not a professional mechanic, but I've got a 07 jeep and 08 Subaru. On either one if I d/c the battery, wait 10 minutes and reconnect the CEL will be there when I restarted, but hit the lights or ignition and really drain it the CEL would clear. Now if it was a legit problem it'd pop back up, maybe after a few seconds, maybe after driving for a day. The POS jeep is bad about having random issues from elevation changes, like vail pass. I've reset it on the side of the road a few times using that method since sometimes it'll actually effect how it's running, but d/c the battery, turn the key with the lights on, reconnect batt. and it'll go back to normal, and CEL won't come back.

Also had to use that method for clearing codes on a 97 f150 I had years ago (first OBDII vehicle I ever owned). Had a vacuum leak that was giving me a lean code and wouldn't clear on its own even after it was repaired, seemed easier than driving back to napa to use the scan tool.

The way I understand it the control module has a capacitor in it that supplies enough power to hold the information, and it can hold out for a very very long time, that's why you turn on the ignition or something else to drain it. Kind of the same way your BIOS settings on your PC stay even with the power off until that little button battery on the motherboard goes dead and then you're redoing all the settings every time you turn it back on.

I could be way off on all of this but it's how I've always understood that stuff to work on the newer cars. The really new stuff might have some sort of solid state memory that doesn't need power.

[JMBD2112]

In most vehicles It's actually a rollover valve to help prevent fuel spillage in an accident. It shouldn't cause an evap code because it doesn't seal anything, the gas cap does. Kinda hard to diagnose a vehicle from the computer. If you're ever down in my neck of the woods anytime soon you can use my scanner

[sniper7]

I just want to know why you were trying to steal your own gas?

[StagLefty]

I just want to know why you were trying to steal your own gas?

Read first post.

[sniper7]

Read first post.

I know I was just kidding

I'll just:

[Skully]

I just want to know why you were trying to steal your own gas?

It is a new thing all the cool kids are doing these days.

Read first post.

I hope you not in some way blaming me for your "Check engine light" I didn't ask you to stick your hose thingy down the filler.

Serious note I have this feeling it is a coincidence. If you look at the filler / line down to the tank if you see wires to a sensor then maybe but I have never seen a sensor in that area. Newer cars do tell you if you need to replace your gas cap. Wife's 2008 Commander (the one I was trying to transfer the gas out) did it to us, it has a dedicated idiot light that lite up and said "check engine gas cap." sure as shit simple fix. I believe the fuel system is closed loop and somewhere there is a sensor that tells the computer it has a pressure leak and figures it is the gas cap. Not sure how it knows it is that or a leak with the carbon canister or lines.

How far have you gotten to figure it out?

[StagLefty]

Getting with Bogie today hopefully. He has one of those scanner thingies.
Skully on advice of my lawyer I can't discuss this with you

[tmleadr03]

It is a new thing all the cool kids are doing these days.

It pressurizes the system and measures the drop of pressure. A large amount o pressure drop means it is most likely the gas cap since otherwise it would be a small hole elsewhere in the system. So a slower pressure drop. More of an educated guess then a "known" variable.

I hope you not in some way blaming me for your "Check engine light" I didn't ask you to stick your hose thingy down the filler.

Serious note I have this feeling it is a coincidence. If you look at the filler / line down to the tank if you see wires to a sensor then maybe but I have never seen a sensor in that area. Newer cars do tell you if you need to replace your gas cap. Wife's 2008 Commander (the one I was trying to transfer the gas out) did it to us, it has a dedicated idiot light that lite up and said "check engine gas cap." sure as shit simple fix. I believe the fuel system is closed loop and somewhere there is a sensor that tells the computer it has a pressure leak and figures it is the gas cap. Not sure how it knows it is that or a leak with the carbon canister or lines.

How far have you gotten to figure it out?

Formatting error being blamed on posting from cell phone.