2001 Saturn SL1, 175,000 miles
Could anyone help me to narrow down the items to troubleshoot here? I have simultaneous P0140 (O2 sensor) and P0446 (evap vent control circuit) codes. Does the combination of these codes point to anything specific? The P0446 came first. Didn’t even have a chance to start troubleshooting that one before it was followed by the P0140 code about 200 miles later.
I appreciate any guidance anyone can offer. Thanks.
One has nothing to do with the other.
P0140 means the O2 sensor is dead.
And P0446 means the vent valve/circuit for the EVAP system is malfunctioning.
Tester
Check the wire harness(s) that goes to both
If the wires to both The O2 sensor and the Vent Control got melted on the exhaust, it could possibly give both codes
BTW, it is the rear O2 sensor, the one behind the cat, usually behind the first cat but could be behind the second cat. The first O2 sensor should be in the exhaust manifold just before the warm up cat.
P0140: Make sure the 10A emissions fuse is ok. HO2S-2 sensor could be faulty but problematic wiring/connectors from the fuse block (for the heater), or wiring between sensor and PCM possible culprits as well. PCM itself could be faulty too. This would normally be diagnosed by a shop using a scan tool capable of displaying the voltage-vs0time sensor output waveforms. So consider hiring a shop to provide the diagnosis, then you can do the repair yourself if you like.
P0446: Evap system required to be air-tight from fuel tank to purge valve. Drivetrain computer tests the evap system’s air-tightness by opening purge valve & closing vent valve. Evap system vacuum builds (b/c engine is drawing vacuum on purge side), the vent valve is opened, and vacuum should quickly decrease. In your case it isn’t.
Vent valve not opening upon PCM command, vent valve is plugged, corresponding hose is plugged, evap canister problem, pressure sensor not working, PCM not issuing command to open vent valve, something along those lines. My guess, vent valve plugged or faulty. Next in line, wiring or connector problem; after that, pressure sensor faulty. Be sure to first check fuse for this circuit, appears to be 30A, named for some bizarre reason “cruise 1”.
Always a good idea to repair the lowest code first, so start with the P0140.