P0443 Evaporative Emission Control System Purge Control Valve circuit Malfunction
On my 99 Montero I've got this code coming up. From what I've been able to find is that it's the relief valve for the charcoal canister. The valve is always open but the valve itself is fine. It's not getting a signal to close to let the system build up any pressure. The valve always has 12 volts going to it when the key is on but there is no ground. I tried cutting the ground wire and leaving it disconnected or grounding it but both ways it then throws the same code plus
P0446 - Evap Emission Control Vent Circuit Malfunction
when I hook the ground back up the 446 code goes away. Every post I've read says it's either the valve, wiring, or ECU. I don't want to replace the ECU without eliminating everything else. So my question is. What tells the ECU that the valve needs to be energized, it seems to me that the computer getting a signal to close the valve is more likely than the ECU causing the problem. However electronics are not my strongest subject. Thanks for any help.

 

To cause a P0443, there has to be a problem with the purge control circuit and it could be any of the following: Bad purge solenoid (internal short or open), Wiring harness chafing or rubbing another component causing short or open on control circuit, Connector worn, broken or shorted due to water intrusion or Driver circuit inside powertrain control module (PCM) is bad.

You can try this: Using a scan tool, command the purge solenoid to activate. Listen or feel for a clicking coming from the purge solenoid. It should click once, or on some models it may click repeatedly. If it doesn't click with scan tool activation, unplug the connector and examing the solenoid and connector for damage, water, etc. Then check for battery voltage on the feed wire with the key on. If you have battery voltage, then ground the control side manually using a jumper wire and see if the valve clicks. If it does, then you know the solenoid is working properly but there is a problem with the control circuit. If it doesn't click when you manually ground it, replace the purge solenoid. To check for a problem on the control circuit (if the solenoid tests okay and you have voltage to the solenoid) plug the solenoid back in and remove the control circuit (ground) wire from the ECM connector (If you're unsure how to do this, do not attempt). With the ground wire removed from the ECM, turn the key on and then manually ground the Purge valve control wire. The solenoid should click. If it does, then you know there is no problem with the control wire to the solenoid and there is a problem with the ECM purge solenoid driver circuit in the ECM. You'll need a new ECM. However if it doesn't click, then there must be an open in the wiring between the ECM and and the solenoid. You must find it and repair it.

A code P0446 could mean one or more of the following has happened: Faulty vent valve, Open, short or excessive resistance on Vent valve control circuit, Blockage of vent valve or Bad PCM. With a P0446 OBD-II trouble code, here are some things to try: Replace Vent valve, Repair open, short, or resistance problem in control circuit or in power circuit and Replace PCM.