Technical Description of OBD-II Trouble Code
The Purge Flow Sensor Circuit is experiencing intermittent issues.
What does that signify?
This generic powertrain/engine diagnostic trouble code can be applicable to all engines equipped with OBDII, but it is more commonly found in certain Mercedes Benz vehicles.
The Purge Flow Sensor (PFS) is typically located 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 / 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, in addition to 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 checks the voltage signal from the PFS sensor to verify its accuracy during initial Key On.
P0469 may have been triggered due to mechanical issues (typically related to the EVAP system) or electrical issues (PFS sensor circuit). These factors should not be overlooked during the troubleshooting process, especially when dealing with an intermittent problem.
Troubleshooting steps may vary depending on the manufacturer, type of PFS sensor, and wire colors.
Severity & Symptoms
The severity depends on the nature of the failure. If it is a mechanical failure, it is considered severe. If it is an electrical failure, it is not as severe, as the PCM can compensate adequately for it.
Symptoms of a P0469 engine code may include:
Potential Causes
The typical causes for this code to be triggered are:
Diagnostic and Repair Procedures
A good starting point is always to search for any technical service bulletins (TSBs) related to your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogram available 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 in the top of the fuel tank / fuel pump module. Once located, visually inspect the connector and wiring. Look for any signs of scraping, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connector and carefully examine the terminals (the metal parts) inside the connector. Check for any signs of burning or green tint indicating corrosion. If needed, clean the terminals using electrical contact cleaner and a plastic bristle brush. Allow them to dry and apply electrical grease to the contact points.
If you have a scan tool, clear the diagnostic trouble codes from the memory and see if the P0469 code returns. If it does not, then the issue was most likely related to the connections.
If the P0469 code does return, further testing of the PFS sensor and its associated circuits will be necessary. With the Key Off, disconnect the electrical connector at the PFS sensor. Connect the black lead of a Digital Voltmeter to the ground terminal of the PFS sensor wiring harness connector. Connect the red lead of the Digital Voltmeter to the power terminal of 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, the signal wire needs to be tested. 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 P0469 code, it is most likely indicating a failed PFS sensor. However, 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.
