What this code means
This code may mean the fuel vapor system is not sealing well enough during the PCM’s leak check.
What the vehicle may do
- The MIL may be on.
- The truck may otherwise drive normally.
- A fuel vapor odor may be possible depending on where a leak is located.
Possible fault areas
- EVAP hoses, tubes, and sealing points may be involved.
- The charcoal canister area may be involved.
- Fuel tank sealing areas may be involved.
- The ESIM switch, wiring, mounting seal, or internal vent valves may be involved.
- The purge solenoid may be involved.
Diagnostic path
Opening and diagnostic setup
On this Ram, P0455 is an EVAP system large leak fault. In plain terms, the PCM may be seeing that the sealed fuel vapor system cannot hold vacuum the way it should. The truck may simply have the MIL on and may otherwise drive normally, but the possible fault areas can include EVAP plumbing and sealing points, the charcoal canister area, fuel tank sealing areas, the ESIM switch or its wiring and mounting seal, ESIM internal vent valves, or a purge solenoid that is leaking. If other EVAP codes are present, check what they mean first, then stay focused on the large-leak path. Start with the basic system checks, and remember that temperature swings can skew EVAP results by either masking a leak or making a sealed system look like it leaked.
Monitor gate and set logic
For P0455, treat the running conditions as monitor gates, not as a repair direction. Before the leak-isolation work, keep the ESIM timing and pressure logic in mind. The small leak monitor uses an engine on/drive cycle for a minimum of 2-5 minutes, and the Engine on timer is clipped to a maximum of 26 minutes on any given trip. After shutdown, there is a 12 minute delay time in which the PCM will ignore ESIM Switch input. The engine-off event can run after a maximum time of 17.5 hours without an ESIM Switch closure during the event. For the small-leak accumulation fail timer, the values are Engine on - 100 minutes and Engine off - 70 hours. A related general EVAP failure is when vacuum cannot be created below -250 Pa within a calibrated time. This large-leak diagnostic runs on a cold start after the small leak test failed during the last valid ignition-off event, with ambient temperature between 4°C and 35°C (39°F and 95°F), fuel level between 12% and 88%, and elevation below 8000 feet. Inside the ESIM, the relief valves regulate the system pressure between approximately 1” H2O and -2” H2O (250Pa and -500Pa). When the system vacuum reaches between (-187Pa) and (-250Pa), it acts on the diaphragm and closes the vacuum switch. The ESIM Signal will typically be a 12.0 volt or 5.0 volt signal depending on the vehicle, and the voltage signals can vary between vehicles and may be somewhere between 5.0 and 12.0 volts. The P0455 fault sets when the PCM runs an intrusive leak-size check and the ESIM switch opens before the calibrated time, which points to a large leak being present.
Check updates first
Before you get deep into leak testing, check for any applicable bulletins or PCM flash updates related to this fault. If one applies, perform it, then leak test the system to make sure the system is not leaking before continuing. If there is nothing applicable, move on to the verification routine.
Run the scan-tool verification routine
Turn the ignition on and run the Small Leak Verification Test routine with the scan tool. Follow the screen prompts and document the results from each phase. If the routine passes, the system may be sealed at that moment, so compare the routine results against the expected manual test behavior before doing any repair. If the routine fails, or the routine is not available or will not run, continue into the manual EVAP leak evaluation. Keep in mind, that scan-tool routine is based on the FTP sensor pressure reading. The ESIM switch state is not factored into the routine decision, even though the PCM uses the ESIM switch for leak detection.
Manual EVAP evaluation setup
For the manual leak evaluation, monitor and document Purge Duty Cycle %, ESIM Switch State, and Fuel Tank Pressure: Pa through the five phases. For best results, the fuel tank should be less than 95% of Fuel Tank capacity. Treat this manual check as diagnostic guidance, not an absolute pass-fail by itself, because fuel amount, tank and system size, barometric pressure, ambient temperature, and fuel temperature can all affect what you see.
Manual phases one and two
Phase one is your zero reference. With the ignition on, vent the system to atmosphere and watch the ESIM switch and FTP sensor. You can vent it by removing the gas cap, opening the capless filler, or actuating the purge solenoid for one minute with the scan tool. The ESIM switch should be open, and the FTP sensor should read near zero. It may not be exactly zero, so use the vented reading as your zero reference. If the ESIM reads closed here, think about a grounded ESIM signal wire, a stuck-closed ESIM switch, or a purge solenoid that did not open if you used that method. Phase two is the non-intrusive leak check. Close the system, leave the ignition on with the engine off, and monitor the fuel tank pressure for 2-3 minutes. The reading should slowly move positive or negative. If it stays steady, there may be a leak, or the temperature may simply be too stable to move pressure, so keep testing. If the pressure changes more than 200 Pa in 1 minute, the system is too unstable to test accurately.
Manual phases three, four, and five
Phase three checks for a purge solenoid leak. Start the engine, with the purge solenoid off, and document the ESIM switch and FTP sensor within 5-10 seconds. A small vacuum is normally created as fuel is pulled from the tank, typically between approximately -25 and -50 Pa. If vacuum appears instantly and is near or below the ESIM regulation point of -500 PA, suspect the purge solenoid is leaking. Phase four starts the intrusive leak check and checks ESIM switch function. Let purge become active long enough to create maximum vacuum and stabilize, then shut the engine off immediately after maximum vacuum is reached. The recommended approach is to turn the engine off after the phase three readings, run the purge-vapor test with the scan tool, follow the screen prompts, and once purge is active and vacuum is created, shut the engine off and return to the data display. Fuel tank pressure should drop quickly to approximately -600 Pa, and the ESIM switch should change to closed. If pressure drops but the ESIM does not close, look at the switch and its signal or ground circuit. If the ESIM closes but pressure barely changes, look for a restriction between the canister and FTP sensor or a stuck sensor, and verify the 5-Volt supply before condemning the sensor. If neither the switch closes nor pressure changes, you may be dealing with a very large leak or a purge solenoid that is not opening. If vacuum is 2 to 3 times higher than expected, think about a plugged canister vent hose or fresh air filter, or an ESIM vacuum vent valve stuck closed. Phase five is the intrusive leak check. Once maximum vacuum is created and stable, turn the engine off and monitor the FTP sensor and ESIM switch for an additional 3-4 minutes. The FTP reading should quickly return to approximately -500 Pa and stabilize. Vacuum should stay below approximately -250 Pa, and the ESIM switch should remain closed for that additional 3-4 minutes. If pressure rises quickly near zero or above -250 Pa and the ESIM opens within 3-4 minutes, continue to leak-check the system. If every phase looks correct, the system is most likely not leaking at that time; possible intermittent causes include software issues, debris that cleared from the purge solenoid or ESIM relief valves, or an ESIM that is not mounted correctly with the switch at the 3 o’clock position.
Choose the leak-check method
Once the manual test points to an active leak, choose how you want to isolate it. You can test the EVAP system as a whole, or you can split the system at the charcoal canister and test the fuel-tank side and fresh-air side separately. Either way, the goal is to prove whether the leak is inside the ESIM vent valves or somewhere else in the EVAP system.
Whole-system EELD check
For the whole-system test, use Kit, EELD And Accessory 8404C. Connect the red lead to Battery positive, the black lead to Battery negative, and connect shop air. Set the smoke-air control to AIR. Start the air flow with the remote, block the AIR supply tip while pressing the remote, and verify or set the red flag alignment on the air flow meter. Then connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip to the adapter, activate air flow, and compare the indicator ball to the red flag. If the indicator ball drops to the bottom of the meter or below the red flag, the rest of the system is sealed and the leak is coming from the vent valves inside the ESIM. If it is a capless system that failed the small leak test but passed this pressure test, verify the filler neck is not leaking and continue with the fuel-tank-side check before replacing the ESIM. If the system has a filler cap, replace the ESIM. If the ball stays above the red flag, the leak is not from the ESIM vent valves. Find the leak with smoke, a Hydrocarbon Sniffer, or a bubble test around the connections and sealing points. To check the purge solenoid for an internal leak, remove the manifold hose from the purge solenoid, fill the system with smoke, and look for smoke coming through the purge solenoid. If smoke is present there, replace the purge solenoid. After the repair, run the intrusive leak evaluation again.
Split the system at the canister
If you choose to split the system, remove the canister tube that connects to the fuel tank on the other end from the charcoal canister. Attach a hand vacuum pump to the fitting on the canister, then pump it until the ESIM switch closes. Monitor the ESIM switch with the scan tool for up to 10 minutes. With the fuel tank vapors isolated, the ESIM switch should stay closed if there is no leak and there is little temperature change. If the ESIM switch stays closed for a minimum of 5 minutes, the leak is on the fuel-tank side. If it does not stay closed for a minimum of 5 minutes, the leak is on the fresh-air, or canister, side.
Fuel-tank-side leak check
For a fuel-tank-side leak, use Kit, EELD And Accessory 8404C. Connect the red lead to Battery positive, the black lead to Battery negative, and connect shop air. Set the smoke-air control switch to Smoke. Attach the black hose to the canister tube, press the remote button, and fill the fuel-tank side of the system with smoke. Then use smoke, a Hydrocarbon Sniffer, or a bubble test to locate the leak. Repair or replace the leaking component. If you need to check the purge solenoid internally, remove the manifold hose from the purge solenoid, fill the system with smoke, and check for smoke coming through the purge solenoid. If smoke is present, replace the purge solenoid. Then perform the intrusive leak evaluation again to verify the repair.
Fresh-air-side leak check
For a fresh-air-side leak, use Kit, EELD And Accessory 8404C. Connect the red lead to Battery positive, the black lead to Battery negative, and connect shop air. Set the smoke-air control switch to AIR. Start air flow with the remote, block the AIR supply tip while pressing the remote, verify or set the red flag alignment, connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip to the adapter, and compare the indicator ball to the red flag. If the ball drops to the bottom of the air flow meter or below the red flag, the leak is coming from the ESIM vent valves, so replace the ESIM. If the ball stays above the red flag, the leak is somewhere else on that side. Use smoke, a Hydrocarbon Sniffer, or a bubble test around the connections and sealing points. For an internal purge solenoid leak check, remove the manifold hose, fill the system with smoke, and check for smoke through the purge solenoid. If smoke is present, replace the purge solenoid. Then repeat the intrusive leak evaluation to verify the repair.
Verify the repair and closing takeaway
Keep verification separate from leak isolation. After the leak is repaired, run the intrusive leak evaluation again and confirm the system holds vacuum as expected and the code stays gone. The main takeaway on P0455 is simple: do not guess at common EVAP parts. Prove the system response with the scan data, then use the leak test to isolate whether the fault is in the ESIM vent valves, the fuel-tank side, the fresh-air side, or the purge path. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0455 should be diagnosed by proving the system response first, then isolating the leak location instead of guessing at parts.
For more guided automotive diagnostics, visit STEP Diagnostics.
