P0455: P0455 Diagnostic Guide

What this code means

P0455 may mean the EVAP system is not building the expected purge or sealing response, often described as a possible large vapor leak or no-purge-flow concern.

What the vehicle may do

The vehicle may drive normally with the check engine light on.
There may be a noticeable fuel odor near the engine compartment, EVAP canister, or fuel tank area.
There may be an audible vacuum noise if the leak or restriction is significant.

Possible fault areas

Possible filler cap or capless filler sealing issue
Possible EVAP hose, line, canister, or fuel tank sealing issue
Possible purge valve, vent valve, or fuel tank pressure signal concern
Possible fuel vapor restriction affecting purge flow

Diagnostic path

Opening context

On this F-150 with the 2.7 EcoBoost, P0455 points to an EVAP monitor concern where the PCM may be seeing no purge flow, a large vapor leak, or more than one smaller leak while the system is being checked. The truck may run normally, but the check engine light can be on, and there may be a fuel odor or an obvious vacuum noise around the engine compartment, EVAP canister, or fuel tank area. Think of this as a command-and-response EVAP diagnosis: seal the system, command the valves, watch the fuel tank pressure signal, then prove whether the system can hold pressure.

Safety and setup gates

Before disconnecting any fuel tubes or fuel system components, relieve fuel system pressure. Fuel can remain under high pressure even with the engine off. Handle fuel with spill and ignition precautions in mind. When using the Evaporative Emission Leak Detector With On Board Nitrogen Generator 218-522C or equivalent, the fuel tank must be less than 85% full. Also, do not apply smoke to the EVAP leak detection control module. For leak searching, a soap solution around the filler area or using a hydrocarbon emission analyzer is not recommended.

Start with the basic system checks

Start with the basic system checks and run the PCM evaporative emissions system test if the scan tool supports it. If that test is not available, keep moving. After that, check for codes. If other codes are present, check what they mean first. For this episode, if P0455 is present, continue down the EVAP large-leak and no-purge-flow path. If P0455 is not present, pause this path and use the no-code or symptom-based direction instead.

Initial visual and filler checks

Next, visually inspect the capless fuel tank filler pipe or fuel cap area, along with the EVAP lines and hoses, for damage or incorrect connections. Run the canister purge valve check on the scan tool if it is available. If you find a concern here, repair it as needed, clear the PCM codes, repeat the self-test, and rerun the PCM evaporative emissions system test. If nothing obvious shows up, move deeper into the filler and sealing checks. If the vehicle has a fuel cap, look at it before disturbing it. Make sure the tether is visible and free to move, and check for a missing, loose, or damaged cap. If it has a capless filler, inspect the inlet before disturbing it. Look for debris that can keep it from sealing and check the filler pipe for damage. Install and remove the supplemental fueling adapter five times in the capless fuel tank filler pipe to help clear debris on the seal, then repeat the check. If the scan tool can run the purge valve check, run it again here. For P0455, also pay attention to audible vacuum noise or a strong fuel odor around the engine compartment, EVAP canister, and fuel tank area.

Check for restrictions and sensor plausibility

With the ignition off, inspect for a restricted vacuum hose between the EVAP canister purge valve and the engine intake manifold. Also inspect the fuel vapor tube between the purge valve and the EVAP leak detection control module if equipped, and check for a damaged fuel filler pipe or fuel tank. On this 2.7 EcoBoost path, if a concern is found, repair it as needed, then verify with the PCM evaporative emissions system test, clear the PCM codes, and repeat the self-test. If no concern is found, open the system at the filler: on a capless filler, install the supplemental refueling adapter; otherwise, remove the fuel cap. Turn the ignition on, access the PCM, and monitor the FTP_V PID. For listed hybrid applications, the FTP PID range is between 1.409 - 1.54 volts. For all others, including this 2.7 EcoBoost path, the FTP PID should read between 2.1 - 2.9 volts. If it is outside the applicable range, install a new FTP sensor, repeat the test, verify the result, and then continue into leak verification.

Command the EVAP valves and watch the response

If the FTP signal is in range, close the system again by installing the fuel cap or removing the supplemental refueling adapter. Start the engine. Command the EVAP canister vent valve closed by setting EVAPCV to ON, 100% duty cycle. Then monitor FTP_V while commanding the purge valve open in steps, up to 100% on the EVAPCP PID. You are looking for a response: the FTP PID decreasing, an engine RPM change, or the engine stalling. Any of those shows the purge valve is opening. If there is no response, install a new EVAP canister purge valve, repeat the test, verify the result, and continue into the pressure verification path.

Set up the leak detector

Now set up the Evaporative Emission Leak Detector With On Board Nitrogen Generator 218-522C or equivalent. With the ignition off, disconnect the fuel vapor-to-EVAP canister line at the EVAP canister purge valve and connect a suitable hose adapter to that line connection. If the hook-up is not complete or does not make sense, pause and get the leak detector connected correctly before continuing. Do not guess on the connection.

Smoke-test the EVAP system

For smoke testing, remove the fuel cap or install the supplemental refueling adapter. Connect the smoke supply to the adapter and set the leak detector to SMOKE. Turn the ignition on, access the PCM, and close the EVAP canister vent valve by commanding EVAPCV to ON, 100% duty cycle. Start the smoke supply and verify the connection at the purge-valve-side fuel vapor line is not leaking. If smoke does not come out of the fuel tank filler pipe after the system is pressurized, command the vent valve open. Once smoke is seen at the EVAP canister vent valve, command the vent valve closed again. When smoke exits the fuel tank filler pipe, install the fuel cap or remove the supplemental refueling adapter, then continue applying smoke to the EVAP system. Use a halogen spotlight along the EVAP path and look for smoke at the leak. Check hoses, the purge and vent valve areas, the canister, fuel tank, filler pipe, tank area, and the cap or capless inlet. Wiggle components and connections while watching for smoke. If smoke is not found, remember that pressurized smoke may not reach a leak in the filler pipe area between the check valve and the cap or capless inlet, so visually inspect that area again. If you locate the leak, repair as needed, reconnect everything, run the PCM evaporative emissions system test, and then move to pressure verification. If no leak is located, reconnect everything and still move to pressure verification.

Leak verification pressure test

For the pressure check, calibrate the flowmeter using the 0.020 standard. Connect the supply hose to the vehicle through the suitable adapter and set the leak detector to the 0.020 standard. Turn the ignition on, access the PCM, and close the EVAP canister vent valve by commanding EVAPCV to ON, 100% duty cycle. Start the pressure supply. The flowmeter ball will start at the top while the system is being pressurized. Keep pressurizing until the ball stops descending, then compare it to the red pointer flag. If the measurement is below the indicator flag, the EVAP system passes the pressure test. If it is above the indicator flag, the system still has an unacceptable leak, so go back to the smoke leak search instead of guessing. For P0455, if the EVAP system passes this pressure test, continue to the purge valve leak check.

Purge valve leak check and final confirmation

With P0455, a passed system pressure test is not the end of the path. Run the canister purge valve check with the scan tool. If that check is not available, remove the EVAP canister purge valve, connect a suitable adapter at the fuel vapor-to-EVAP canister connection, connect the supply hose, and start the pressure supply. Let the flowmeter ball settle and compare it to the red pointer flag. Below the flag means the purge valve passes the pressure test. Above the flag means the purge valve has an unacceptable leak; install a new EVAP canister purge valve, run the PCM evaporative emissions system test, clear the PCM codes, and repeat the self-test. If the purge valve passes and no concerns are present, clear the PCM codes and repeat the self-test. The takeaway: prove the seal, prove the FTP signal and purge response, find any leak with smoke, and finish by verifying pressure and purge valve sealing. For more diagnostic training, visit stepdiagnostics.com.