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P1457 EVAP canister leak 1998-1999

Old 08-06-2009, 01:36 PM
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Default P1457 EVAP canister leak 1998-1999

I wrote this years ago on another site (when I owned a 1998). Lately there's been several threads about it, so here it is again. Strictly speaking, it applies to 1998 & 1999 4-cylinder Accords. I don't own that Helm book any more, so I can't look up the remainder of the procedure.

I have a feeling it's almost identical for any 1998-2002 Accord. Maybe even similar for 7th-gen Accord?

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 like it should be.

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 closed, it should hold vacuum when the solenoid is not energized. When the solenoid valve is energized, it should not hold vacuum.

************ THANKS to rjpjnk for the following clarification about this valve.
The 2 way valve is complicated. It should hold vacuum on the lower port when the solenoid is *not* energized. The solenoid when energized provides a passageway to bypass the normal path between the upper port and the lower port. That's why it is called a "bypass solenoid" btw.

The upper port of this wretched valve from pluto is actually designed to open to pass vacuum or pressure to the lower port when the vacuum or pressure exceeds a certain threshold (a kind of hysteresis effect). The slight resistance to flow is what allows a certain design pressure to remain in the fuel tank. Once this is exceeded, the excess pressure (fuel vapor) bleeds over to the canister side. At any time, the ECM can force this to happen by activating the bypass solenoid. It does exactly this during the p1456/p1457 diagnostic tests. The upper side port is always connected to the top port (the third leg of this beast) which is connected directly to the FTP (fuel tank pressure sensor). Did you know the FTP sensor is not in the fuel tank? ;-)

EVAP Canister 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 can 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...

Last edited by JimBlake; 09-09-2009 at 07:34 AM. Reason: fixed the part on the 2-way valve
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