Is your engine light on?
August 27, 2024 3:44 PM Subscribe
Is your engine light on? Have you been told it probably indicates a vapor leak?
My very good garage mechanic told me the last time I took my auto in for an oil change that the engine light on meant s possible vapor leak...which would have to be fixed before my next emissions control check. My state requires this. He said it involves dropping the gas tank and inspecting the hoses and whatnot. Seemed reasonable to me...Estimate wasn't cheap. So I told my handyman next door neighbor who owns every tool known to man. He asked if I had checked the gas cap. I had not. He came over the next day and proceeded to wipe down the little rubber gasket in the gas cap. Then he put a small amount of white mechanics grease around the gasket. I put the cap back on the tank, turned on the auto, and the engine light was gone. It has been three weeks and it is still off. I bought him a bag of caramels.
My very good garage mechanic told me the last time I took my auto in for an oil change that the engine light on meant s possible vapor leak...which would have to be fixed before my next emissions control check. My state requires this. He said it involves dropping the gas tank and inspecting the hoses and whatnot. Seemed reasonable to me...Estimate wasn't cheap. So I told my handyman next door neighbor who owns every tool known to man. He asked if I had checked the gas cap. I had not. He came over the next day and proceeded to wipe down the little rubber gasket in the gas cap. Then he put a small amount of white mechanics grease around the gasket. I put the cap back on the tank, turned on the auto, and the engine light was gone. It has been three weeks and it is still off. I bought him a bag of caramels.
Not an unfamiliar problem. Mechanic's grease is a good solution, or you could also try a new gas cap. I have found that a code reader is a useful thing to carry in case of Check Engine light--that might help you identify any additional instances of a small evaporative leak.
posted by MonkeyToes at 4:12 PM on August 27 [1 favorite]
posted by MonkeyToes at 4:12 PM on August 27 [1 favorite]
There's a lot of different reasons the check engine light might be on. Some are serious and you can wreck your car by ignoring them. Others are not a big deal at all, though at least in California if the check engine light is lit or has been recently you can't get your car emissions certified which is sometimes required for renewing registration.
ODB2 scanners are inexpensive and can read and clear error codes. Interpreting them is not trivial but you can usually google them to get a sense of how urgent they are.
If cleaning the gas lid fixed it though, then sure that probably was the problem!
posted by aubilenon at 4:18 PM on August 27 [1 favorite]
ODB2 scanners are inexpensive and can read and clear error codes. Interpreting them is not trivial but you can usually google them to get a sense of how urgent they are.
If cleaning the gas lid fixed it though, then sure that probably was the problem!
posted by aubilenon at 4:18 PM on August 27 [1 favorite]
Not sure what you're asking here. The mechanic was not trying to scam you, though sometimes dropping the tank is required. There are numerous parts involved in keeping an air tight seal on the gas tank and the gas cap is the one you interact with most often so it's easiest to check first. But the evap leak code could have been another related component (hoses, solenoids, charcoal canister) which would require diagnosing the leak. You probably wouldn't jump straight into dropping the tank, for instance you can use a smoke machine to pressurize the system and visually see where the leak is. But fixing it might require e.g. replacing the seal around the sending unit and that requires dropping the tank. Mechanics will go to the worst case scenario when giving a quote, that doesn't mean it will always work out that way. Hopefully they would have checked the gas cap first, because again that is like, super basic super well known first step that anyone can do.
posted by Rhomboid at 5:12 PM on August 27 [2 favorites]
posted by Rhomboid at 5:12 PM on August 27 [2 favorites]
Oh and if you're asking about how the check engine light knows that you cleaned the gas cap, the computer monitors the vapor pressure in the tank. It knows when the pressure should rise (e.g. sitting parked on a hot day) and when it should fall, particularly when the computer opens a solenoid that allows manifold vacuum to pull out excess vapor from the tank and canister. If either of those things fail (pressure not building or releasing) then there's a problem in the evap system and it sets a code.
posted by Rhomboid at 5:25 PM on August 27 [2 favorites]
posted by Rhomboid at 5:25 PM on August 27 [2 favorites]
Yes, and my mechanic recommended fixing the gas cap because it was 'easier' than dealing with looking at the entire fuel system. It bought me some time until the inlet control valve started going wonky and prevented me from putting more than a squeeze of gas at a time. After a year of trying to convince my mechanic there was a problem, we got the system unstuck which bought me some time until one day the valve stopped working altogether and the fuel overflowed and ruined the entire fuel system, which cost me over 3k to fix. (There are probably more details I am missing because I was just OVER IT.)
If this is a Jeep this crap is common. Even if it isn't, fix it as soon as you can because it'll be cheaper in the long run than buying time to save money.
posted by kimberussell at 6:15 PM on August 27
If this is a Jeep this crap is common. Even if it isn't, fix it as soon as you can because it'll be cheaper in the long run than buying time to save money.
posted by kimberussell at 6:15 PM on August 27
Know a neighbor with an OBD-II scanner?
This gadget plugs under your car dashboard and it is essentially the same device as what mechanics use to "pull codes": these "codes" are readouts from the computers on your car that tell the mechanic what is wrong, and are what help them fix the problem.
With this scanner in hand, you can do this read-out yourself and see why that check-engine-light comes on, and you can do a little research on the "code" that comes out to see if your mechanic is blowing smoke or telling you the truth about what's wrong and what needs fixing.
For example, in your case, the OBD-II scanner could tell you there is an oxygen sensor issue. This can be dealt with by tightening the gas cap on your car, which your newly-carameled neighbor helped with by greasing the cap and helping form a tighter seal.
posted by They sucked his brains out! at 7:18 PM on August 27
This gadget plugs under your car dashboard and it is essentially the same device as what mechanics use to "pull codes": these "codes" are readouts from the computers on your car that tell the mechanic what is wrong, and are what help them fix the problem.
With this scanner in hand, you can do this read-out yourself and see why that check-engine-light comes on, and you can do a little research on the "code" that comes out to see if your mechanic is blowing smoke or telling you the truth about what's wrong and what needs fixing.
For example, in your case, the OBD-II scanner could tell you there is an oxygen sensor issue. This can be dealt with by tightening the gas cap on your car, which your newly-carameled neighbor helped with by greasing the cap and helping form a tighter seal.
posted by They sucked his brains out! at 7:18 PM on August 27
…and get your emissions done when the check engine light is off, if is it’s due, don’t procrastinate. Mechanics can reset the codes say, when you have a catalytic converter replaced as well.
A gas cap replacement has gotten me through with a previous vehicle.
posted by childofTethys at 8:35 PM on August 27
A gas cap replacement has gotten me through with a previous vehicle.
posted by childofTethys at 8:35 PM on August 27
Seems legit! I had a similar issue with a Hyundai Elantra, and yes, the gas cap was to blame. Fantastic neighbour you have :)
posted by tamarack at 10:08 PM on August 27
posted by tamarack at 10:08 PM on August 27
Be aware that OBD scanners range from very basic to much more comprehensive. The basic ones, often self-contained like this very cheap Topdon unit that was the first one I bought, will read and reset a common set of industry-standard error condition codes and should cover most causes of a Check Engine light showing on the dash. Any condition you reset without actually fixing the underlying defect will just come straight back, so just resetting everything is a fairly safe first response to an initial Check Engine because glitches do happen.
Fancier units that use an app running on a Bluetooth-connected phone as their UI will also know what to do with manufacturer-specific codes, letting you work with subsystems such as airbag and braking whose diagnostics are apparently not yet fully covered by industry standards. The Bluetooth types are more physically convenient as well; some vehicle manufacturers hide their OBD connectors in truly weird places.
The Autel dongle I bought after little ms flabdablet accidentally disabled all the airbags in her Misubishi Triton by removing and replacing a front seat for cleaning came with an app and a subscription service for keeping its code sets up to date. Even including that, it still cost me less than getting the airbag fault code reset at a dealer's.
posted by flabdablet at 4:45 AM on August 28
Fancier units that use an app running on a Bluetooth-connected phone as their UI will also know what to do with manufacturer-specific codes, letting you work with subsystems such as airbag and braking whose diagnostics are apparently not yet fully covered by industry standards. The Bluetooth types are more physically convenient as well; some vehicle manufacturers hide their OBD connectors in truly weird places.
The Autel dongle I bought after little ms flabdablet accidentally disabled all the airbags in her Misubishi Triton by removing and replacing a front seat for cleaning came with an app and a subscription service for keeping its code sets up to date. Even including that, it still cost me less than getting the airbag fault code reset at a dealer's.
posted by flabdablet at 4:45 AM on August 28
Further to that, at the risk of a minor derail: if you're going to remove a seat from a somewhat modern car, and you find that it's connected to the wiring loom via a little plug and socket, do not assume that that's just for the in-seat heater. Disconnect the car battery completely and leave it sit for 30 seconds before you unplug the seat, lest you too find yourself with all your airbags disabled after the computer registers the seat unplug event as a fault.
posted by flabdablet at 5:05 AM on August 28
posted by flabdablet at 5:05 AM on August 28
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posted by Mo Nickels at 4:08 PM on August 27