P0455: P0455 Diagnostic Guide

What this code means

P0455 may indicate that the EVAP system is not sealing as expected during its leak monitor.

What the vehicle may do

The vehicle may only show a check engine light.
A fuel odor can be possible in some EVAP leak situations.
Driveability is often not noticeably affected.

Possible fault areas

A possible fuel fill sealing issue may be involved.
EVAP hoses, pipes, or the canister may be involved.
The purge or vent side of the EVAP system may be involved.

Diagnostic path

Open on P0455

On this 2019 to 2025 Silverado 1500 with the 5.3 gas engine, P0455 is an EVAP leak code. In plain language, the fuel vapor system may not be sealing the way the monitor expects, and the controller is seeing EVAP purge system leakage greater than a predefined threshold. The driver may only notice a check engine light, though fuel odor can be possible, and driveability is often not noticeably affected. The broad areas to keep in mind are the fuel fill sealing point, EVAP hoses and pipes, the canister, the purge side, and the vent side.

Start with the basics

Start with the basic system checks before you get into the EVAP leak test. If other codes are present, check what they mean first, then follow a structured diagnostic approach. Before touching the system, make sure you understand the EVAP layout well enough to know what you are sealing, what you are commanding closed, and where the test pressure or smoke is being introduced.

Visual and physical inspection

Now do the first pass inspection. Check the purge solenoid, vent solenoid, canister, EVAP hoses and pipes, and the fuel fill sealing point. You are looking for anything disconnected, incorrectly connected, loose, leaking, kinked, restricted, missing, stuck open where applicable, or visibly damaged. On a cap-style fill, pay attention to the cap. On a capless fill, pay attention to the filler door sealing area. If you find one of those conditions, repair it or replace the affected part as necessary before moving on.

Prepare the EVAP tester

If that inspection is clean, set up the GE-41413-A, B, or C EVAP tester. Review the tester safety information and operating guidance before testing. Make sure the vehicle underbody temperature and the tester temperature are similar. Completely unwind the nitrogen and smoke hose from the bracket so the tester can work correctly. Also keep the EVAP test pressure under control: pressure must not exceed 13 in H2O (0.5 PSI), because more than that can make system components act inaccurately. For the tester setup, install the hose at the Test Orifice — 0.51 mm (0.020 in), select Nitrogen, turn the remote switch on, align the sliding red flag with the floating indicator, turn the remote switch back off, and remove the hose from the test orifice.

Connect to the EVAP system and check flow

Next, disconnect the quick connect fitting at the Q12 EVAP purge solenoid valve. Install the CH-48096 EVAP service port access tool between the EVAP canister purge tube and the Q12 purge solenoid valve, then connect the EVAP tester hose to that access tool. Put the ignition on with the vehicle in Service Mode. With the scan tool, command the EVAP vent solenoid valve to Not Venting. Turn the tester remote switch on and watch the floating indicator. The expected result is the floating indicator below the sliding red flag. Be patient here: larger fuel tanks, or tanks with lower fuel levels, may take several minutes for the floating indicator to stabilize or for smoke to show from a leak.

If the indicator is not below the flag

If the floating indicator is not below the sliding red flag, turn the tester off and switch to Smoke. When injecting smoke, remove the fuel fill cap or temporarily leave the EVAP vent valve open until smoke is observed, then close the system. Confirm smoke has filled the system by opening it at the opposite end from where smoke is being injected. For intermittent leaks, move the related EVAP components while smoke is applied. Then turn the tester on, use the high intensity white light to inspect the EVAP areas of concern, and verify whether smoke is exiting anywhere. If smoke is coming out of a component or part of the system, repair it or replace the affected part as necessary. If no smoke leak shows up on that path, go back to the beginning of the diagnostic path and recheck it rather than guessing.

If the indicator is below the flag

If the floating indicator is below the sliding red flag, the leak test is passing at that point. Now reproduce the operating conditions for the P0455 monitor, or reproduce the captured conditions, and verify that the code does not reset. Treat these as monitor gates, not a diagnosis by themselves: Q12 Evaporative Emission Purge Solenoid Valve flow greater than 2.0%; Barometric Pressure Sensor greater than 70 kPa (10.1 PSI); Fuel Level Sensor 10 to 90%; Ignition Voltage greater than 10.0 V; Start-Up Engine Coolant Temperature Sensor and Start-Up Intake Air Temperature Sensor within 8°C (14°F) of each other; Start-Up Engine Coolant Temperature Sensor less than 35°C (95°F); and Start-Up Intake Air Temperature Sensor 4 to 35°C (39 to 95°F). If P0455 sets again, repeat the diagnostic path from the beginning. If it does not set, the result is all OK.

Repair verification and close

After any repair is completed, verify the repair and confirm the code stays gone. Takeaway: do not parts-swap a P0455. Inspect the sealing points first, use the EVAP tester correctly, let the floating indicator decide whether you move into smoke testing, and then prove the monitor passes afterward. For more diagnostic training, visit stepdiagnostics.com.