2006 Colorado P0446 Code: Purge Valve Not Opening Despite Power - Diagnosis & Fix
Hello, I'm experiencing a P0446 diagnostic trouble code on my 2006 Chevrolet Colorado. After testing both the vent control valve and purge valve individually, I've confirmed that the vent valve closes properly when initiating the EVAP system test via a bidirectional scan tool. However, during the same EVAP test cycle, I do not hear the purge valve open. The purge valve terminal has power (12V), but no ground signal is being sent from the PCM — this ground is normally initiated by the PCM driver. The engine is cold and I have approximately half a tank of fuel. I've tested voltage across the two terminals of the purge valve using a multimeter, which reads 12V. However, when I connect my test light (incandescent type) to these terminals, it does not illuminate. My multimeter is brand new and functioning correctly. This discrepancy — reading 12V on the meter but no power to the test light — has me confused. I understand that a bidirectional scan tool should activate both valves during an EVAP system test. If the purge valve isn't opening, why isn't it responding? Could this be due to high resistance in the control circuit or a failure in the PCM's ground signal? What steps can I take to verify the purge valve circuit is fully functional? Thanks for any insight — Scott
While I haven't personally used a bidirectional scan tool for EVAP testing, it's reasonable to expect both valves should activate during the test. The multimeter reads 12V because it draws minimal current — typically just a few milliamps — whereas an incandescent test light requires around 150–200 milliamps to illuminate. This explains why your meter shows voltage but the test light doesn't. Since you've confirmed the purge valve opens when tested independently, this suggests the issue lies in either the feed or control circuit (e.g., high resistance) or a failure on the PCM side to provide the proper ground signal. Recommended troubleshooting steps: - Use a test light with a chassis ground reference to verify the purge valve circuit. This can be done while the solenoid is connected. - BBBind.com provides an EVAP wiring schematic showing the path from the purge valve to the PCM, which may help trace the circuit. - If the test light shows no response, the issue likely lies in the control wire or the PCM not sending a ground signal. If it works, then the problem is likely with the PCM's control output. This approach helps isolate whether the fault is in the wiring or the electronic control module.