P0446 code on 2000 Corolla

[bigsilentrob]

My check engine light came on Friday afternoon so I went and had codes run on it yesterday. It came back with this.

P0446
EVAP Emission Control System
Vent Circuit Malfunction


I recently accidently left my oil cap off last week when putting oil in and it was left off for a couple of days. Is this possibly what caused my check engine light to come on? Is this something that I should be concerned about? Thanks for any help.

Rob

[Brian R.]

Could be:
Open or short in VSV circuit for vapor pressure sensor
VSV for vapor pressure sensor
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
Open or short in VSV circuit for EVAP
VSV for EVAP
Vacuum hose cracks, hole, blocked, damaged or disconnected
Charcoal canister cracks, hole, or damaged

1. Check the VSV connector for EVAP, VSV connector for vapor pressure sensor and vapor pressure sensor connector for looseness and disconnection

2. Check the vacuum hose between intake manifold and VSV for EVAP, VSV for EVAP and charcoal canister, charcoal canister and VSV for vapor pressure sensor, and VSV for vapor pressure sensor and vapor pressure sensor. Check these hoses for correct connection, looseness, cracks, holes, damage, and blockage.

3. Check voltage between terminals VC and E2 of ECM connector (4.5-5.5 V). (replace ECM if faulty)

4. Check voltages between terminals PTNK and E2 of ECM connector while applying vacuum to vapor pressure sensor (2.9-3.7 V).

If faulty, check for open and short in harness and connector between vapor pressure sensor and ECM. If ok at this point, replace vapor pressure sensor.

If voltage above is ok, Check VSV for EVAP. When ECM terminal EVP is grounded (ignition "ON"), Air should flow in pipe E (inboard on tube) on VSV and out F (outboard on tube) on VSV (Don't use high pressure air for this test). When EVP is not grounded, air does not flow in E and out F.

5. Check operation of VSV for EVAP. Remove VSV from engine. Check that there is continuity between the two terminals (30-34 ohms). If there is no continuity, replace VSV for EVAP.

Check that there is no continuity between either terminal and body. If there is continuity, replace VSV for EVAP.

Check that air does not flow from inner port (E) to outboard port (F).

Check that air flows from port E to F when you apply battery voltage across terminals. If no air flows, replace VSV for EVAP.

6. Check the vacuum hose between intake manifold and VSV for EVAP, and VSV for EVAP and charcoal canister. Check as above.

7. Check for open or short in harness and connector between EFI main-relay and VSV for EVAP and ECM. If faulty, repair or replace harness or connector. If ok, check and replace ECM.

8. Check VSV for vapor pressure sensor. When ECM terminal TPC is grounded (ignition "ON"), Air should flow in pipe E (inboard on tube) on VSV and out F (outboard on tube) on VSV. When TPC is not grounded, air flows out G (outside of connector).

If ok, check and replace charcoal canister.

If not functioning correctly, check function of VSV for vapor pressure sensor. Remove from engine.
Check that there is continuity between the terminals (33-39 ohms). Replace the VSV if there is no continuity.

Check that air flows from port E (inboard in tube) to port G (side of connector).

Check that air flows from port E to port F (outboard in tube) when battery voltage is applied across terminals. Replace VSV if function is incorrect.

9. If good, Check the vacuum hose between charcoal canister and VSV for vapor pressure sensor, and vapor pressure sensor and VSV for vapor pressure sensor - check as above.

11. Check for open and short in harness and connector between EFI main replay and VSV for vapor pressure sensor and ECM.