1999 Eclipse GST Spyder PO446: Vent Solenoid Voltage Issue and Diagnosis

This applies to the 2.4L model? The vent solenoid has two wires: one red, one blue/red. Confirm wire colors and configuration to ensure we're discussing the correct model. If accurate, the red wire receives 12V from the MFI relay circuit — same as fuel injectors. The vehicle would not start without this power supply. However, it's possible you have a different engine variant.

No, it's a 2.0L turbo model. Same wiring configuration. After rechecking, I do get voltage on the red wire — but the solenoid still won't close when powered. When I disconnect and apply 12V directly to the solenoid, it closes properly. This suggests either a ground fault or an issue with the ECM signaling via the switching wire.

The vent valve is normally open (N.O.) and receives 12V when the key is on (KOEO). The red wire supplies power; the blue/red wire is a 'switching' signal that runs from the solenoid to the PCM. The PCM monitors for 12V on this signal wire — if it's absent, it may trigger PO446. When conditions are met, the PCM grounds this switching wire, causing the N.O. vent valve to close. It expects to see a voltage drop when commanded. Therefore, if the solenoid doesn't close under normal operation, the issue could be an open, shorted, or grounded signal wire. Recommended steps: Use a scanner to command the valve closure (if available), otherwise probe the switching wire at the PCM connector with a multimeter. Also check for corrosion and ensure the connector is tight. Test both wires at the solenoid — 12V on both should be present when key is on. Unplug the vent solenoid and verify the signal wire isn't grounded before testing the PCM end of the circuit.

I only see 12V on the red wire with the key on. The blue/red wire reads about -0.3V — essentially near ground. I've tested the solenoid resistance and it shows 20 ohms, confirming it's functional. I suspect a wiring issue or ECM fault. Do you know where the PCM connector is located in my 1999 Eclipse GST Spyder?

With the vent solenoid connector plugged in — are there 12V on both wires? - Without a proper ground, voltage should be present on both wires. Check the electrical connector for loose connections or corrosion. Is the switching wire grounded? This is critical to diagnosing whether the PCM can send a command.

I'll use some T-pins to test voltage while the connector is plugged in. Is there a better method than using T-pins? How do I determine if the switching wire is grounded?

In professional diagnostics, we'd use a scanner to command the PCM to ground the vent valve — this requires more than just a code reader and can be expensive. A digital multimeter (DVOM) with a wire piercing probe (also known as a power probe) is a better alternative for testing signal wires without removing connectors.

Thank you all for the help. The issue was a broken wiring harness under the driver's seat that caused an open circuit in the switching wire.