What does it mean?
This generic powertrain/engine diagnostic code can generally apply to all OBDII-equipped engines but appears more frequently in certain Mercedes Benz vehicles.
The Purge Flow Sensor (PFS) is typically mounted in the evaporative fuel system, also known as the charcoal canister, near the fuel tank or possibly even in the top of the fuel tank module/fuel pump. The PFS converts EVAP system pressure into an electrical signal for the Powertrain Control Module (PCM).
The PCM receives this voltage signal to determine the amount of fuel it will put into the engine as well as the fuel entering the EVAP system intake manifold. This code is set if this input does not match the normal engine operating conditions stored in the PCM’s memory, even for a second, as indicated by this diagnostic code. It also checks the PFS sensor voltage signal to determine if it is correct at initial key-on.
P0466 could have been set due to mechanical issues (typically EVAP system mechanical problems) or electrical issues (PFS sensor circuit). These cannot be overlooked during the troubleshooting phase, especially when dealing with an intermittent issue.
Troubleshooting steps may vary depending on the manufacturer, PFS sensor type, and wire colors.
Severity and Symptoms
Severity depends on the failure. In case of mechanical failure: severe. In case of electrical failure: less severe, which the PCM can adequately compensate for.
Symptoms of a P0466 engine code may include:
Malfunction Indicator Lamp (MIL) illuminated
Decreased fuel economy
Potential Causes
Typically, causes for this code to set include:
Open in the signal circuit to the PFS sensor – possible
Short to voltage in the signal circuit to the PFS sensor – possible
Short to ground in the signal circuit to the PFS sensor – possible
Open in power or ground at the PFS sensor – possible
Failed PFS sensor – probable
Failed PCM – unlikely
Diagnostic and Repair Procedures
A good starting point is always researching a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogramming to address this issue, and it’s worth checking before discovering you’ve taken a long/wrong path.
Next, locate the purge flow sensor on your specific vehicle. This sensor is typically mounted in the evaporative fuel system, also known as the charcoal canister, near the fuel tank or possibly even at the top of the fuel tank module/fuel pump. Once located, visually inspect the connector and wiring. Look for scratches, rubbing, bare wires, burns, or melted plastic. Separate the connector and carefully inspect the terminals (the metal parts) inside the connector. Check if they appear burned or have a greenish tint indicating corrosion. Use electrical contact cleaner and a plastic bristle brush if terminal cleaning is necessary. Let it dry and apply electrical grease where the terminals make contact.
If you have a scan tool, clear the diagnostic codes from memory and see if the P0466 code returns. If not, the connections were likely your problem.
If the P0466 code returns, we’ll need to test the PFS sensor and its associated circuits. With the key off, disconnect the electrical connector from the PFS sensor. Connect a black wire from the digital voltmeter to the ground terminal at the PFS sensor wiring harness connector. Connect the red wire from the digital voltmeter to the power terminal at the PFS sensor wiring harness connector. Turn the key to engine off. Check manufacturer specifications; the voltmeter should read 12 volts or 5 volts. If not, repair the power or ground wire or replace the PCM.
If the previous test passes, we’ll need to test the signal wire. With the connector still disconnected, move the red voltmeter wire from the power wire terminal to the signal wire terminal. The voltmeter should now read 5 volts. If not, repair the signal wire or replace the PCM.
If all previous tests pass and you continue to get a P0466, this would most likely indicate a failing PFS sensor, although a faulty PCM cannot be ruled out until the PFS sensor has been replaced. When in doubt, seek assistance from a qualified automotive diagnostician. PCMs need to be programmed or calibrated to the vehicle to be installed properly.