Vehicle: 2000 Mercury Sable, V6-3.0L DOHC, VIN S, Automatic Transmission/Transaxle

Mileage: 96,267 Miles

Problem: The Sable came in with an illuminated malfunction indicator light (MIL). The vehicle seemed to run normally.

Case Details: The technician found diagnostic trouble code (DTC) P0443 – Evaporative Emission Control System Purge Control Valve Circuit Malfunction, so he replaced both the vent valve and the evaporative solenoid. He cleared the DTC, but it came right back.

After finding 12 volts on both wires for the evaporative solenoid and vent valve, he called ALLDATA Tech-Assist. The Tech-Assist consultant gave the technician the following advice.

He recommended testing the wire from the purge solenoid valve to the computer for a ground while the computer was commanding the purge solenoid on. NOTE: That command could be found in the special tests section of a scan tool. He said that if there was still no ground at the valves, test it again at the PCM connector. If the ground was good there, the problem would likely be a break in the wire. If there was no break in the wire, the next probable cause would be a defective PCM.

The consultant also sent the technician the following information about diagnosing DTC P0443.

The key detail in the DTC P0443 description is “Circuit Malfunction.” This indicates the concern is electrical, not necessarily a mechanical failure of the purge valve itself.

The EVAP canister purge valve is typically located in the engine compartment. The PCM controls the purge valve by supplying a variable duty cycle signal (0–100%) to the solenoid. With the key on, there should be battery voltage (B+) present on the red wire (circuit 381). The gray/yellow wire (circuit 101) is the PCM-controlled pulse-width modulated (PWM) ground.

To test the control circuit:

1. Connect a test light to B+.
2. Probe circuit 101 (GY/YE wire).
3. Command the purge valve on using a scan tool.

If the circuit is functioning properly, the test light should illuminate or pulse in response to the commanded duty cycle.

While commanding the valve on, there was no ground at the purge valve or PCM wires.

Confirmed Repair: The technician replaced the defective PCM and gave the car a good road test. No DTCs returned, and the car ran fine. Fixed!