Hello,
I have searched the threads but have not found too much on this. I have an '04 4Runner with 198K miles. V6, 2WD, SR5. For the last 6 months or so we have been getting an intermittent (pretty strong) smell of gasoline inside the vehicle. I can also sometimes smell it standing outside of the vehicle. In addition, I have the CEL, and VSC/TRAC lights on. When it first starts up it also seems to idle high for longer than it used to. It takes a couple of minutes to settle back to normal idle RPM. Other than that it runs fine. I suspected this was an issue with the EVAP system. Today I took it to the dealer and paid $100 to have them do a diagnostic. I was hoping they might be familiar with a gas smell issue in an '04 4Runner but they were not. BTW the gas cap was replaced by me a few months ago. Anyway...The dealer could not smell anything (my bad luck) and basically just read the codes. They didn't do any real investigating. To my surprise, they said there were no EVAP codes. There were codes for A/F Sensor Bank 1, Sensor 1, and A/F Sensor Bank 2, Sensor 1. So... first I plan to replace those sensors and would appreciate any advice on replacing them. Second, I am at a loss regarding the gas smell. My understanding is that the fuel system is supposed to be sealed and if it's not I should see a code.

The codes I have are P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1) and P0051 A/F sensor heater control circuit low (Bank 2, Sensor 1)

Sorry for the long post. I would appreciate any help. Thanks.

If I'm not mistaken, the AF sensors are the top two Oxygen sensors in the manifolds. Simple enough to replace. Rock auto has decent prices at $80ish each. The tabs are a little tricky to unclick, but any auto store has the O2 removal wrench that'll help access the sensors.

If that's the issue, it'll run rich and you'll likely notice fuel smell. When mine were bad, it was even coating my exhaust pipe

Thank you!

Do buy the recommended O2 sensors, OEM or NTK (maybe Denso?) I think. They are pricier but work properly. One other thing to mention is that I believe when I got my truck both upper sensors threw a code so I replaced them. I found that there's a fuse that powers the heater on both of them that was also bad. Knowing the code numbers you have would be useful.

Thanks, good advice. I purchased the Denso sensors this morning. It looks like there are 3 and got all 3. Pricey for sure. The dealer didn't give me the codes but I have a OBDII reader and am going to try and get them myself. I will post back.

So I was able to pull the codes. They are P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1) and P0051 A/F sensor heater control circuit low (Bank 2, Sensor 1).

Those are the exact codes I had. Search on them and you'll find some threads on the fuse. For sure check it as you may have the same issue.

Actually, I think these also use the crappy relay that sticks on which can burn the heater circuits out. I would replace that A/F relay before running the car with the new sensors. I have had no issues with mine since doing this a few years ago.

Here's a couple threads I found.
Simultaneous P0031 and P0051 Codes
Swapped out O2 sensors and getting P0031 and P0051
P0031 and P0051 Codes - Check Engine Light, VSC TRAC, VSC OFF Light - The Track Ahead

Really appreciate the links Mike. I will check them for sure.

I have heard that if you continue to pump gas into your tank after the nozzle has clicked off, gas can get into the EVAP canister, the charcoal canister in the engine compartment that captures gas tank emissions after the engine has been turned off. This will cause a strong smell of gas in the cabin.

You might try just replacing that part and see if it helps

That is definitely a possibility as I have done that before when heading out on a long trip. The carbon filter is darn expensive! Thank you.

If I'm not mistaken the charcoal cannister is not under the hood but at the back of the vehicle near the fuel door, if it was under the hood pumping in to much gas could not get into it, but at the back near the fuel door it can certainly get in there from overfilling.

Correct. I can see it back there near the fuel door.

Hey Mike... so following your advice, and trying the simple things first, I swapped the Dome light relay and the A/F relay (they are the same). Bingo! CEL was gone and at first, the VSC and VSC Trac lights were off too. The dome lights no longer worked so definitely a bad relay. However, as soon as I put the 4runner in gear and moved the VSC and Trac lights returned. The CEL remained off. So I checked for codes. There were none. All clear. So that led me to search for VSC/Trac lights on no codes. I came across a video that explained I would likely just need to do a zero-point calibration of the system by jumping pins on the OBDII port. I did that and everything has cleared! So thanks to you I am returning almost $400 in sensors. The relay was less than $20. BTW the dealer wanted $1021.82 to replace those two sensors. They quoted $639.98 for just the sensor parts alone. Crazy but the craziest thing is changing them out would not have corrected the issue as it was a common power feed problem going to the sensors via the cheap relay, not bad sensors. Anyway, I cannot thank you enough for taking the time to help me. Have a great weekend.
Here is the video:
https://www.youtube.com/watch?v=rUA5Qko-v6A

But did it fix your strong fuel smell?...

No it didn't. I'm certain these two issues are not related. Now that the lights are gone I plan to zero in on the gas fumes.