Technical Description of OBD-II Trouble Code
The circuit for the Purge Flow Sensor is experiencing high levels of flow.
What does that signify?
This generic diagnostic trouble code for powertrain/engines can typically be applied to all engines equipped with OBDII, but it appears more frequently in certain Mercedes Benz vehicles.
The Purge Flow Sensor (PFS) is usually located 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/fuel pump module. The PFS converts the pressure in the EVAP system into an electrical signal for the Powertrain Control Module (PCM).
The PCM uses this voltage signal to determine the amount of fuel it will inject into the engine, along with the fuel entering the intake manifold from the EVAP system. This code is triggered if this input does not match the normal engine operating conditions stored in the PCM’s memory, even for a brief moment, as demonstrated by this diagnostic trouble code. It also examines the voltage signal from the PFS sensor to determine if it is correct during initial Key On.
P0468 is set when the voltage at the sensor remains above a certain level (usually over 4.8V) for an extended period of time. This code is typically attributed to an electrical circuit issue.
Troubleshooting steps may vary depending on the manufacturer, type of PFS sensor, and wire colors.
Severity & Symptoms
In this case, the severity is not severe. Since it is an electrical failure, the PCM can compensate adequately for it.
Symptoms of a P0468 engine code may include:
Potential Causes
Typically, the causes for this code to be triggered are:
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/reprogram to address this issue, and it is worth checking before going down a potentially lengthy and incorrect path.
Next, locate the purge flow sensor on your specific vehicle. This sensor is usually found 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/fuel pump module. Once located, visually inspect the connector and wiring. Look for any scraping, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connector and carefully examine the terminals (the metal parts) inside the connector. Check if they appear burned or have a green tint indicating corrosion. If necessary, use electrical contact cleaner and a plastic bristle brush to clean the terminals. Allow them to dry and apply electrical grease where the terminals make contact.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the P0468 code returns. If it does not, then the connections were most likely the issue.
If the P0468 code does return, we will need to test the PFS sensor and its associated circuits. With the Key Off, disconnect the electrical connector at the PFS sensor. Connect the black lead of a Digital Voltmeter to the ground terminal at the PFS sensor wiring harness connector. Connect the red lead of the Digital Voltmeter to the power terminal at the PFS sensor wiring harness connector. Turn the Key On Engine Off. Check the manufacturer’s specifications; the voltmeter should read either 12 volts or 5 volts. If not, repair the power or ground wire, or replace the PCM.
If the previous test passed, we will need to test the signal wire. With the connector still disconnected, move the red lead of the voltmeter 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 have passed and you continue to receive a P0468, this most likely indicates a failed PFS sensor, although a failed PCM cannot be ruled out until the PFS sensor has been replaced. If unsure, seek assistance from a trained automotive diagnostician. PCMs must be programmed or calibrated to the vehicle in order to be installed correctly.
