What does it mean?
This generic powertrain/engine diagnostic code can generally apply to all OBDII-equipped engines but appears more frequently in some 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 perhaps even in the upper part 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’s 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’s voltage signal to determine if it is correct at the initial key-on.
P0468 is set when the voltage at the sensor remains above a defined level (usually above 4.8 V) for too long. This code is generally considered an electrical circuit issue.
Troubleshooting steps may vary depending on the manufacturer, PFS sensor type, and wire colors.
Severity and Symptoms
The severity in this case will not be serious. Since it is an electrical failure, the PCM can adequately compensate.
Symptoms of a P0468 engine code may include:
Malfunction Indicator Light (MIL) illuminated
Decreased fuel economy
Potential Causes
Typically, the causes for this code to set are:
Short to power in the PFS sensor signal circuit – possible
Open in the ground circuit to the PFS sensor – likely
Failed PFS sensor – possible
Failed PCM – unlikely
Diagnostic and Repair Procedures
A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogramming to address this issue, and it is 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 perhaps 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. See if they appear burnt or have a greenish tint indicating corrosion. Use electrical contact cleaner and a plastic-bristled brush if terminal cleaning is needed. 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 P0468 code returns. If not, the connections were likely your problem.
If the P0468 code returns, we will 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 supply terminal at the PFS sensor wiring harness connector. Turn the key to the engine-off position. Check the manufacturer’s 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 will 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 P0468, this would most likely indicate a faulty PFS sensor, although a faulty PCM cannot be ruled out until the PFS sensor has been replaced. If in doubt, seek assistance from a qualified automotive diagnostician. PCMs need to be programmed or calibrated to the vehicle to be installed correctly.