Check engine light due to gas cap

Guys, my check engine light was on this morning.
Turns out it’s because my gas cap gasket was thin, sending out an emissions code.
Has anyone heard of this!w/the gen 1? Glad it’s nothing serious but that is unreal!

 

Fairly common for a faulty gas cap to throw a code actually. Not unique to the Tundra either.

 

Yeah, that's pretty common with these trucks. It's not a bad idea to buy a new OEM gas cap from a dealer at the age of these now. Rubber, and plastic get brittle/dry rotted over time.

I've put one new gas cap on everything but the corolla. Heard of this problem but never experienced it for myself

 

Yep. Happened to me. Common issue on all cars with OBDII.

 

Stealership got me boys. Wish I had searched the forum first.

 

Or at least all EFI engines with emissions/EVAP in particular for sure.

The fuel system is sealed and works on a vacuum/purge system to hold a very specific pressure. Obviously, if your gas cap isn't firmly fastened with at least 1 click, then it cannot properly seal the tank, i.e. you're leaking vacuum.

It's not unreal, it's just the design virtually all modern auto makers use today. Where the purge valves exist is variable. There's almost always a charcoal/absorptive container somewhere to collect excess fumes and/or return them to be ignited too.

 

Uh-oh. What happened?

Also, I'm in the bad gas cap group.

 

The gasket in my OEM cracked and gave me CEL. I was in East Boofoo so I got an aftermarket and put the gasket on my OEM. Worked fine after that.

 

First thing I do with EVAP/emissions codes which suggest a leak is present is try to tighten the gas cap. If it's already tightened all the way, I replace the gas cap with new, legit OEM.

It's solved my issue on a couple of vehicles now, but sometimes w/EVAP codes you neverk now. A couple GM trucks I owned had issues with an EVAP vent solenoid near the gas tank getting jammed up with mud. That was a fun one...

 

My 99’ Tacoma actually went into limp mode cause of a bad gas cap.

$42 at the dealer, and it solved the problem.

 

These aren't '68 trucks anymore. Mileage and emissions are much better due to systems design.

How'd the dealer get you? Reading the code? FLAPS will do that for free or code readers can be purchased for DiY diagnosis.

Enjoy the Tundra!

 

That’s just wrong.

 

Yeah, bummer, but we all make mistakes.

When it happened to me, I was in town, had my code reader with me so I looked it up, reset the code, drove home, ordered a new gas cap for like $18? And it never happened again. Only code my truck has ever thrown in fact while I've owned it.

Emissions maybe...not so sure about mileage.

 

Greetings All,

I just joined the Tundras.com forum - aka new member - hello everyone!

My Tundra needs regular scheduled 100k maintenance. I thought I would do things right and ask questions in the forum before scheduling. So what is the most pressing question an owner of a magnificent 2003 Toyota Tundra might ask? Well, I typed in 'check engine light gas cap' - lo and behold this week it appears to be a topic of discussion. If ever there was an invitation to join Tundras.com, this is it!

RE[CAP]PING

$40 gas cap.

$140 if you let the mechanic do it.

New gas cap, reset the system by disconnecting the battery. No more light!

Well, not so fast... 20 years of light coming back on after 2 weeks.

20 years of $140 gas caps.

Here's the kicker - I can disconnect the battery, drive my Tundra around awhile, hit up the smog
check station, pass the smog check, two weeks later the light comes back on... and I didn't have to pay $140 for a gas cap!

SUGGESTED ALTERNATIVE: piece of electrical tape, cut to fit, placed strategically on instrument panel pane. No more check engine light!

 

Have you gone to your friendly local auto parts store to see what codes your engine is throwing? If it's running fine, it's probably the O2s on one bank or the other.

In which case, unless you like clogged cats at $600+/ea and shit gas mileage, is a relatively cheap solution (and if you buy Denso brand O2 sensor, then replace both on the affected bank, you won't see it back on for 20 years). Taping over the light is never a solution, it's a visual band-aid preventing you from seeing when a more serious problem happens and that CEL starts flashing indicating "stop driving me, ASAP"

Anyway, welcome to the forum. Toyota recommends changing the timing belt every 9yr or 90k miles. If you have the V8 (2UZ-FE), and your timing belt breaks, your engine will grenade itself, it's interference. If you haven't done the timing belt in the last 10-12yr/100k-120k miles, that should be your #1 priority right now.

 

So no OBD2 hookup for inspection, just a smog check?

Normally, they'd fail you here if the ODB2 hookup didn't get through it's drive cycles to read all clear. Disconnecting the battery resets it and would require you to go through them once again. Then again, we don't smog so maybe it's check one but not the other. Weird.

 

Dunno where @ToyBoyt is, but I think you may remember in GA, there's a couple of prerequisites. No CEL can be lit, for any reason (airbag or other). OBDII must also report all readiness checks are completed or they won't finish the inspection. They'll turn you away and tell you to come back after driving a couple hundred miles.

Anyway, I guess it could be more than O2. It could also be knock sensors. If @ToyBoyt lives where there's mice, they may've nested up in the intake plenum area.

 

Sounds about right. The good thing for me is that I’m exempt from emissions after 15 years so i just clear any existing or pending codes to insure the light won’t go on during inspection that day.

 

Yes! O2 sensors, I forgot about that. See this is why I wanted to get input here at Tundras.com - help refresh my memory. This is very helpful. I also found some other notes - 'Mass Airflow Sensor'???

Yeah, they did the timing belt / water pump back in 2018 at 85k. That was the last time Tundra was in.

 

I mean, the #1 best thing you can do for yourself right now is to go to a local auto parts store, or buy a decent OBDII code reader, and scan for codes. Parts stores normally do it for free. AutoZone's system will even print out an info sheet telling you likely causes, they'll do anything to get you to buy parts from them. I'd go in, get a free scan, then start a new thread with the code. We can walk you through troubleshooting it.

MAF is one of those things you only replace if there's a suspicion of damage and/or potential fuel/air ratio problem. I would never proactively replace one unless an event came up, like you pulled straight water into your intake, rodents shredded your air filter and that rained paper over the sensor, or there was visible corrosion on it. I don't even bother cleaning them; I know you can, but the risks outweigh the rewards for the at-home armchair mechanic.

I threw a CEL about 2-3 weeks ago out of nowhere. When I scanned for codes, it turned out to a knock sensor detecting pings, likely due to bad gas. I went to a grocery store gas station out of desperation/impatience in the week or so prior, and about 1/3 of the way thru that tank of gas, the code fired out of nowhere, and money light came on. I cleared the code and that was that ... but the engine was running totally normal.

There are a few things that'll toss codes without impacting performance. Lots of emissions related stuff, like minor/major EVAP leaks, SAI pump (but you should hear a high-pitch whistle/screech at startup from that), purge valve, O2 sensors, cats, gas cap are a few of them. Obviously, knock sensors will do it too, as we see from my case - had it been legit, I should've heard audible noise from the engine.

There's no way to know withouth knowing what code tripped the light, though ...

 

What does "I threw a CEL" mean?

All google wants to give me is people throwing their cellphones.

 

Check Engine Light (CEL), aka "money light", "dummy light", etc.

"I threw a CEL" = My money light came. Usually when they come on, it means you're spending your hard end cash on something... or you're a dummy because you forgot something.

 

In the olden days, a CEL meant 'no oil in the engine, it's about to melt, better stop.'

Hey, I found the paperwork from the mechanic dated 2018-0105.

Diagnosis of EVAP CODE PO446. Ran a smoke test and found leak at gas cap seal. Replaced gas
cap and retested for proper seal. System shows no leaks at this time after gas cap replacement. Codes have been cleared from the ECU. LABOR 115.50, PARTS (gas cap) 38.68 TOTAL 154.18

 

Ouch. That's spendy. But they did the right thing to test it.

My previous comment still stands: Scan which codes are triggering the light and share, happy to help you get to the bottom of it.

 

Your wish is my command, sir:

 

Oh, fun fun fun. EVAP related. Nothing to do with O2 or knock sensors.

So, this is supposedly what was fixed previously, small EVAP leak - i.e. you're not holding proper, regulated vacuum in your fuel/emissions system. Smoke test to find the leak would be advised in this case too, to see if/where you're leaking. It could just be the shop didn't use an OEM gas cap, aftermarket gas caps are shitware.

Basically the gist with EVAP is this: You must have a sealed fuel system which holds a constant, known vacuum pressure, from fuel cap to the injector/intake. If something is cracked preventing a constant vacuum, or the purge valve which opens if temporarily if the ECM sees too much vacuum too isn't working correctly, you'll throw EVAP codes like this.

The breakdown of your codes is this:

P0446 => You either have a leak between the fuel cap and injector/intake, or the wiring to the purge valve is shorted/faulty (it's almost always a leak)
P0441 => ECM is detecting invalid vacuum/purge, maybe a leak (broken charcoal canister, loose/missing EVAP hoses, bad gas cap, cracked filler neck) or the purge valve r vacuum switch is shorted/faulty
P0442 => Redundant with the above: You have a small leak. There are separate codes for large leaks. "Small" leak usually means something is cracked and/or not sealing properly, like the seal inside a gas cap is busted, your charcoal canister is cracked, fuel filler neck is cracked, the fuel tank has a pinhole in it, an EVAP rubber hose is cracked. "Large" leak codes would indicate a more massive leak, like a chunk of the charcoal canister was gone, there was no gas cap installed, or similar.​

My first suspicion, if the mechanic used an OEM gas cap is that your fuel filler neck may have a crack in it, or the charcoal canister could have a crack in it. The vent/purge valve on many makes/models is actually on the charcoal canister, so you can check both at same time. Alternately, vent/purge valve or vacuum switch (if used in out 1st gens) may be shot. Only way to really tell quickly would be a smoke test. You can actually buy a decent smoke test kit these days for about what you paid the mechanic.

Chasing down EVAP issues can be a nightmare. Smoke test is usually a great place to start when throwing multiple codes, just to quash the potential of this being a leak.

EDIT: Quick note to say, I had P0446 code throwing a couple of trucks ago, ~2018ish, it was a GM 1500, and it was caused by a failing fuel pump. Basically, I wasn't pumping enough gas to hold expected vacuum. This could also be your case, based on the hesitation and noise when you're accelerating up inclines... But smoke test would still be my 1st step.

 

FWIW...I used to throw a 442 code regularly. I was preparing to one day have to change the purge valve, however, I discovered that my rusty gas tank was in fact leaking. After I replaced it, no more codes.

 

There was a TSB for faulty fuel filler neck on some 1st gen Tundras. Would cause same Check Engine light as loose gas cap. Had it happen with my 04 years ago.

Service advisor told me that I didn’t know how to tighten fuel cap. Gave him my opinion of that and asked if they checked the TSB, which they had not. Fuel filler neck replaced and never had issue again.

 

Yup, great minds think alike. Main reason I mentioned such a specific thing, we've had a couple of guys here with the cracked filler neck. TSB is 0003-11 and it did impact @ToyBoyt's year/model:

2003-2004 Tundra
2003-2004 Tundra Limited
2003-2004 Tundra SR5​

I'm attaching the TSB for this. Actually - there's an updated TSB, thanks @BubbaW, see SEE HERE. 0442 code is one of the symptoms, could be worth looking into.

 

Oh, and in case you're lazy, you can just cross-reference your VIN to this list to see if maybe you're impacted.

Find your model in the left column.
Verify if your VIN number is HIGHER or LOWER than what's printed.
If LOWER, your model is affected, and the person who replaced your gas cap probably charged you for fixing the wrong thing.