Error Code P0466 is defined as Purge Flow Sensor Circuit Range/Performance. Meaning, there’s a performance problem in EVAP system, which could be caused by a faulty part or bad fuel cap.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II, especially those made from 1996 up to the present. It is, however, more common among Mercedes vehicles. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.


The PFS (Purge Flow Sensor) is usually found in the Evaporative fuel system, also called the charcoal canister, and located close to the fuel tank. In some makes and models, it is placed on top of the fuel tank or fuel pump module. This sensor works by converting EVAP system pressure into an electrical signal for the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes).

The PCM uses the signal to determine how much fuel it will have to send into the engine, along with the fuel entering the intake manifold from the EVAP system. Error Code P0465 is set when the input doesn’t match the normal engine operating conditions stored in the memory of the PCM, even for a second. It also checks the voltage signal from the PFS sensor to determine it is right at the initial Key On.

Error Code P0466 can be set when the sensor in the system sends wrong voltage to the PCM. It is usually a mechanical (usually EVAP system mechanical issue) or electrical (PFS sensor circuit) issue. While some vehicles require multiple cycles for the Check Engine light to light up, a code will usually be stored right in the first failure. Stored codes without Check Engine light may be read as pending codes.

Common Symptoms

Symptoms depend on the severity of the conditions, and severity also depends on the failure. If a mechanical failure sets the code, the problem could be severe. If an electrical failure causes it, then it’s not as severe, as the PCM can compensate them adequately for it.

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Also, it increases the fuel consumption of the vehicle.

Possible Causes

  • Loose or defective cap
  • Failed purge control solenoid
  • Broken or clogged charcoal canister
  • Broken, cracked, or deteriorated vacuum/fuel vapor hoses
  • Defective pressure or flow sensor

How to Check

A better starting point for diagnosis of this code is through using Technical Service Bulletin (TSB) and search for your particular vehicle. Sometimes vehicle manufacturer may have a PCM flash/reprogram that covers the problem.

Next, technicians check the flow sensor of the vehicle. The sensor is usually found mounted in the EVAP fuel system, also called as charcoal canister, which is located close to the fuel tank or maybe even on top of the fuel tank or fuel pump module. They inspect its wiring and connectors to look for problems, such as bare wires, burn spots, rubbing, scraping, or melted plastic. Then they pull the connector apart and check the terminals (metal parts) inside the connector. They will look for burned or green tint, which would indicate corrosion. Technicians use electrical contact cleaner and plastic bristle brush to clean the terminals. Then they let it dry and apply electrical grease where terminals meet.

Then they will use the scan tool to clear the codes from the memory and see if the code comes back. If it does not come back, that means the problem was in the connections.

If the code comes back, technicians will proceed on testing the PFS sensor and all of its associated circuits. With Key Off, electrical connectors at the PFS are disconnected. Then, they will connect the DVOM black lead to the ground terminal at the PFS sensor wiring harness connector. The red lead of the DVOM is then connected to the power terminal of the PFS sensor wiring harness connector. They turn the Key On Engine Off and then check with the specifications set by the manufacturer. Voltmeter should read either 12V or 5V. If not, power, ground or PCM must be replaced.

If the vehicle passed the prior test, then there’s no need to test the signal wire. With connector still disconnected, the technician will then proceed on moving the red lead of the voltmeter from the power wire terminal to the signal wire terminal. The voltmeter should now read 5V. If not, then signal wire must be repaired, or the PCM must be replaced.

If after all the repairs the code still appears, this would mean the problem is caused by a failed FPS sensor, though failed PCM should not be ruled out until the PFS sensor had been replaced.

PCM must be programmed or calibrated to the vehicle for it to be installed properly.

How to Fix

Common fixes for this code include:

  • Tightening of the fuel cap
  • Replacement of the fuel cap
  • Replacement of vacuum lines or vapor lines
  • Replacement of charcoal canister
  • Replacement of charcoal canister purge valve and solenoid

Error Code P0466 may not cause drivability problems, but it can cause the vehicle to fail an emission test.

In many cases, people replace EVAP components when the problem is simply caused by a loose fuel cap or a vacuum leak.