P0455: P0455 Diagnostic Guide

What this code means

P0455 means the EVAP system may be seeing a large leak or a condition where it cannot seal as expected.

What the vehicle may do

The vehicle may only turn on the check engine light.
It can often run normally with no driveability complaint.
A fuel odor may be present depending on the leak location.

Possible fault areas

Possible filler cap or capless filler sealing concern.
Possible filler pipe, tank, or vapor line damage.
Possible purge control or purge valve sealing issue.
Possible FTP sensor feedback concern.

Diagnostic path

Set up the P0455 diagnosis

On this 2011 to 2022 F-250 Super Duty with the 6.2 gas engine, P0455 means the EVAP system may be seeing a large leak or a condition where the system cannot seal the way the PCM expects. The truck may only have a check engine light, it can often run normally, and there may be a fuel odor depending on where the concern is. Broadly, think possible filler cap or capless filler sealing trouble, damaged filler or tank hardware, vapor line issues, purge control issues, or FTP feedback that does not match the test condition. Before disconnecting any fuel tubes or fuel system components, relieve fuel system pressure. Fuel can remain under high pressure even with the engine off. Also treat fuel handling seriously and be ready for spillage around hot parts or ignition sources.

Start with the scan tool EVAP leak test

Start with the available scan tool EVAP leak test for the vehicle. If the scan tool has the EVAP leak routine, run it first. If the test passes or fails with P0455, either way, continue into the P0455 diagnostic path instead of stopping there. If other EVAP codes are present, check what they mean first so you stay on the correct branch.

Do the first visual and purge check

Next, inspect the fuel tank, filler pipe, fill cap or capless area, and the EVAP system for wrong connections or obvious damage. Then run the scan tool canister purge valve check when it is available. If you find a concern here, repair it as necessary, clear the PCM codes, repeat the self-test, and run the applicable EVAP leak test. If that visual check does not show a concern for P0455, move into the filler sealing checks.

Handle a vent-control branch only if the code routing sends you there

If the code routing points to the EVAP canister vent control circuit instead of the P0455 leak branch, handle that branch separately before continuing. With the ignition off, disconnect the EVAP canister vent valve connector and measure voltage between VPWR Pin 1 and CANV Pin 2 at that connector. Then turn the ignition on, access the PCM controls, and command the EVAPCV Status PID on and off. If the voltage changes with the command, turn the ignition off and measure vent valve resistance between VPWR Pin 1, component side, and CANV Pin 2, component side. The decision point is whether the resistance is between 40 Ω - 70 Ω. If it is in that range, the concern is not duplicated on that branch; pause and avoid guessing before moving farther away from the P0455 leak path. If resistance is outside that range, install a new EVAP canister vent valve, run the applicable EVAP leak test, clear the PCM codes, and repeat the self-test. If the commanded voltage does not change, check VPWR voltage at Pin 1 of the vent valve connector. It has to be greater than 10.5 V to keep going; if it is not, repair the open circuit, clear the codes, and repeat the self-test. With the ignition off and the PCM disconnected, check CANV circuit resistance between CANV Pin 2 at the vent valve connector and CANV Pin B34 at the PCM connector. Less than 5 Ω keeps you moving; otherwise repair the open circuit. Then check CANV resistance to ground at Pin 2. Greater than 10000 Ω keeps you moving; otherwise repair the short circuit. Finally, with the ignition on, check CANV Pin 2 for a short to voltage. Any voltage present means repair the short circuit. If no voltage is present, that branch moves to connector and PCM operation checks later.

Check the filler sealing area

At the filler area, do not disturb it at first. On a capped system, look for a missing, loose, or damaged cap and make sure the tether is not preventing proper seating. On a capless system, inspect the inlet for sealing debris or damage. Use the supplemental fueling adapter five times to help clear debris from the seal, then run the purge check if it is available. Do not use a soap solution around the cap or capless inlet, and do not use a hydrocarbon analyzer to try to prove the EVAP leak here. If there is a concern, repair it as necessary, use the smoke machine PHASE 1 leak verification pressure test to verify the repair, then continue into the leak-test hookup. If there is no concern, keep moving down the system.

Inspect for restrictions and damage before smoke testing

With the ignition off, inspect for a restricted vacuum hose between the purge valve and the intake manifold, a restricted fuel vapor tube between the purge valve and the leak detection control module if equipped, a damaged filler pipe, and a damaged fuel tank. If anything is found, repair it as necessary, verify with the smoke machine PHASE 1 leak verification pressure test, and continue to the leak-test hookup. If nothing is found on this 6.2 liter path, check the FTP sensor baseline next.

Check FTP sensor baseline

Open the tank to atmosphere for the FTP check. On a capless filler, install the supplemental refueling adaptor. On the capped system, remove the fuel filler cap. Turn the ignition on and watch the FTP voltage PID. The expected range here is between 2.1 V - 2.9 V. If it is in range, go on to the purge flow check. If it is outside that range, install a new FTP sensor, repeat the test and verify the result, then use the smoke machine PHASE 1 leak verification pressure test before continuing.

Command the vent closed and verify purge response

Turn the ignition off, reinstall the fuel filler cap or remove the supplemental refueling adaptor, then start the engine. Close the EVAP canister vent valve by commanding the EVAPCV PID ON at 100% duty cycle. While watching the FTP voltage PID, incrementally command the EVAPCP PID to 100%. If the FTP PID drops, the engine RPM changes, or the engine stalls, that shows the purge valve is opening, so continue to the leak-test hookup. If none of that happens, install a new EVAP canister purge valve, repeat the test and verify the result, then run PHASE 1 leak verification before continuing.

Hook up the EVAP leak detector

With the ignition off, connect the Evaporative Emission Leak Detector With On Board Nitrogen Generator 218-522C or equivalent. Disconnect the fuel vapor to EVAP canister line at the purge valve, then connect a suitable hose adapter to that fuel vapor line connection. When using this leak detector, the fuel level in the fuel tank must be less than 85% full. Also remember that smoke and air flow from this equipment will not pass through liquid fuel, and liquid fuel may be sitting in the filler pipe. If the hookup cannot be completed, pause and use the leak detector maker’s setup information rather than guessing.

Run the smoke leak detection phase

For leak detection, remove the fuel filler cap or install the supplemental refueling adaptor, connect the supply hose to the hose adapter, and set the leak detector to SMOKE. Turn the ignition on and close the EVAP canister vent valve by commanding EVAPCV ON at 100% duty cycle. Start the smoke supply, make sure your hookup is not leaking, and manage the vent command if smoke does not exit the filler pipe. Once smoke exits, reinstall the cap or remove the adaptor, keep applying smoke, and use a halogen spotlight along the EVAP path to find smoke leaving at the leak. If you find the leak, repair as necessary, reconnect anything you disconnected, run the applicable EVAP leak test, clear the PCM codes, and repeat the self-test. If you do not find a leak, reconnect the system and move to the PHASE 1 pressure verification test. Keep in mind that smoke under pressure may not reach a leak between the filler check valve and the cap or capless inlet, so if no smoke is found, visually inspect that filler area again.

Run the pressure verification phase

For PHASE 1 leak verification, calibrate the flowmeter using the 0.020 standard. Connect the supply hose to the vehicle through the adapter and set the leak detector to the 0.020 standard. Turn the ignition on, close the EVAP canister vent valve by commanding EVAPCV ON at 100% duty cycle, start the pressure supply, and let the flowmeter ball stop descending. Compare the measurement to the red pointer flag. If the system fails this pressure test, go back to smoke leak detection. If it passes and P0455 is the code you are chasing, continue to the purge valve leak test.

Finish with the purge valve leak test for P0455

For P0455 after the EVAP system passes the pressure test, check the canister purge valve for leakage. Use the scan tool purge valve check when it is available. If that routine is not available, remove the purge valve, connect a suitable hose adapter at the fuel vapor to EVAP canister connection, connect the supply hose, start the pressure supply, and wait until the flowmeter ball stops descending. Compare that reading to the red pointer flag. If the purge valve passes the leak verification test, there are no concerns present at this time; clear the PCM codes and repeat the self-test. If it does not pass, install a new EVAP canister purge valve, run the applicable EVAP leak test, clear the PCM codes, and repeat the self-test.

If the vent-control branch reaches the PCM check

Only on that separate vent-control branch, if the circuit tests lead all the way to the control module check, disconnect all PCM connectors, inspect for pushed-out pins and corrosion, reconnect every PCM connector, and make sure they seat correctly. Then verify whether the concern is still present. If it is still present, install a new Powertrain Control Module and complete the required programming. If the concern is gone, the system is operating correctly at that time, and the issue may have been a loose or corroded connector.

Takeaway

The key with P0455 is to prove whether the system is leaking, whether the filler area is sealing, whether the FTP signal makes sense, and whether the purge valve can actually seal after the rest of the system passes. Do the checks in order and verify the repair before calling it fixed. For more diagnostic training, visit stepdiagnostics.com.