Gasoline Vapor Leak?
 

The Check Engine light of my 2001 4-cylinder Accord is on. A scan was made at Auto-Zone (good folks!). It indicated one of the following:

1. Gas cap leak (tank not holding pressure). Replaced gas cap. Did not fix the problem.
2. A hose that connects the gas tank to a charcoal absorption canister is leaking or disconnected. My question: Where is this hose and canister located?

Thanks much!!

The EVAP canister is located underneath the car, about under the left-rear seat.

There's 2 different codes for the EVAP system. P1456 for the fuel tank system & P1457 for the canister system. You need the code number to narrow down the possibilities. There's half-dozen solenoid valves, a pressure sensor, a whole bunch of vacuum tubing, etc.

Thank you JimBlake.

The code is P1457.

Another possible clue... unscrewing the gas cap does not produce the familiar sound of gas vapor escaping.

I'll look for something obvious... like a disconnected hose. Beyond that it sounds like a job for the shop.

GliderPilot

Here's something I wrote a long time ago about what to check...
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P1457 won't make the car run bad at all. It just means the EVAP canister & the related system of hoses & valves isn't airtight.

Check this stuff in this order. As soon as you find something that doesn't behave like it should, fix or replace it. Then hope it was the only thing wrong with the system...

Some background for the electrical troubleshooting:
All the solenoid valves have constant +12v supply from the main relay. When the ECM wants to energize a valve, it closes the ground side of it's circuit. If the +12v supply is broken, then the ECM can't energize the valve. If the wire to the ECM is shorted to ground, then the valve is energized even when the ECM doesn't want it to be.

EVAP Purge Control valve - between intake manifold & valve cover.
Valve should be normally closed, so it will hold vacuum when it's not energized. Ground is supplied by pin A6 of the ECM to open the valve. So jumper pin A6 to ground, turn on the ignition, and check again - this time it should NOT hold vacuum.

EVAP 2-way valve - underneath the car roughly under the left-rear seat.
It's a little can with 3 hose barbs & a solenoid valve attached to it. Leave the connection on top, disconnect both on the side, attach MityVac to lower one. Normally open, when the solenoid valve is energized, it should hold vacuum.

EVAP Vent Shut valve - attached to the charcoal canister underneath the car.
Normaly open - when ECM closes pin A4 to ground, it should hold vacuum.

EVAP Charcoal Canister - the big canister under the car, about under the left-rear seat.
Leak test: Connect all the hoses together, plug the Vent Shut valve, connect the MityVac. Pump vacuum while watching the fuel tank pressure (FTP) sensor. You can read FTP sensor voltage with a scan tool, or use a voltmeter between pins A29 & C18 at the ECM. Pump down to 1.5v & it should hold that vacuum for at least 20 seconds.

EVAP 2-way valve vacuum & pressure test.
If you get this far you'll want the manual for a good picture of how to connect the hoses. Keep pumping the vacuum pump & it should stabilize between 6 & 16 mm Hg of vacuum. Then pump pressure, it should stabilize at 8 mm Hg or more of pressure.

Then there's a test of the ORVR Vent Shut valve, which is located on top of the gas tank. You check vacuum & pressure at a couple hoses alongside the fuel filler pipe. If the valve is bad you drop the gas tank to replace it...

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Now, after all that, on my '98 I checked the solenoid valves by unplugging them & applying battery voltage directly by using some jumper wires. My vent-shut valve didn't even click, so I replaced it. Then the CEL never came back.

JimBlake,

Thank you very much! There's is lot of good informatiom in your reply.
I'll report back with my findings after the problem is fixed.

Gliderpilot