My Jeep (2014 Wrangler) had the engine light on, I took it last week to get serviced and the guy said there was no obvious error code for the light being on, so they cleared it and I had to "drive it around" because inspection is due within the next two weeks.

Well a week later - today - and the engine light just came on again, I was planning on getting it inspected tomorrow.

I'm not much of a car expert and this strikes me dumb. Apparently the engine light can come on for many reasons unrelated to emissions and in my case he said there was no clear cause, no emission related error code was present when the serviced it.

But it seem I will automatically fail inspection just because the engine light is on, but that's dumb, surely they can measure the exhaust gases and test it that way?

If I get the code cleared again then I'll have to drive it around once again to get the emission monitors "ready" again.

Anyone here know about this stuff?

 

Petrol or diesel?

 

Petrol or diesel?

Petrol, I ran to O'Reilly's and they printed out the diag code: P0456 something to do with the EVAP system, a slow leak.

I booked it in to my local repair guy, they said they will run a smoke test.

 

Petrol, I ran to O'Reilly's and they printed out the diag code: P0456 something to do with the EVAP system, a slow leak.

I booked it in to my local repair guy, they said they will run a smoke test.

I've gotten that code before. Turned out to be a bad (leaky) gas cap!

 

You can buy an adaptor that goes on the OBD port of your vehicle that connects to your phone that can read and clear codes for not a lot of money.

 

I was also going to suggest the gas cap.
As has already been suggested, the fuel evaporative system relies on air tight connections through the system. The fuel filler cap is the usual suspect. Although it is not the only reason!
You could start by replacing the cap, and hopefully that will be the end of it. Otherwise it could be a cracked canister, faulty lines, a leaking solenoid or defective sensors. Or even the stupid ECM.

Leave the car parked under the sun for several hours. Sniff around and see if you smell gasoline. Focus your attention around the fuel tank.

 

I was also going to suggest the gas cap.
As has already been suggested, the fuel evaporative system relies on air tight connections through the system. The fuel filler cap is the usual suspect. Although it is not the only reason!
You could start by replacing the cap, and hopefully that will be the end of it. Otherwise it could be a cracked canister, faulty lines, a leaking solenoid or defective sensors. Or even the stupid ECM.

Leave the car parked under the sun for several hours. Sniff around and see if you smell gasoline. Focus your attention around the fuel tank.

I scrutinized the cap, it seems perfect, the O-ring looks clean and good as new. Perhaps some silicone grease on that O-ring wouldn't hurt...

 

I had an '07 Corolla that kept showing a similar code. It was under warranty and the dealer swapped out the gas cap twice. The third time they updated the ECM firmware and the problem went away.

My guess is the dealer tried a pressure or vacuum test and, when that failed, reverted to the most common, easiest fix, the gas cap. See what your local guy says.

 

That's a common code and problem. It's often the gas cap but my leak was a cracked rubber hose at the canister. It wasn't easy to get to and looked fine by visual inspection. But I went ahead and slipped it off the plastic hose barb and sure enough, there was a crack in the hose parallel to the hose's long dimension. I just cut off that half inch and put it back on. Lasted years after that.

An OBD reader is under $20 and is a good investment, if you care to do any DIY stuff. For one thing it'll allow you to clear all error codes, so you can tell quickly if a problem is still present. Otherwise it may not reset itself for days even after you've made a fix.