What this code means
P0455 may indicate that the EVAP system is not holding vacuum as expected during a leak check, often described as a large EVAP leak condition.
What the vehicle may do
- The MIL may be on.
- The vehicle may otherwise seem to run normally.
- There can be possible refueling complaints if the vent side is restricted.
Possible fault areas
- Possible EVAP hose, tank, canister, or filler sealing leak areas.
- Possible ESIM switch, vent valve, or mounting-related concerns.
- Possible purge solenoid leakage or command response concerns.
- Possible FTP sensor or ESIM signal and ground circuit concerns.
Diagnostic path
Opening and setup
On this 2019 through 2025 Ram 1500DT with the 3.6 Pentastar, P0455 is an EVAP large leak fault. In plain terms, the PCM ran an EVAP leak check and saw the system lose vacuum sooner than expected, so the MIL will illuminate. The driver may not notice much besides the light, but the fault area can involve a possible leak path, capless filler or filler sealing issue, EVAP hoses, the canister area, ESIM operation, purge flow, or related sensor and switch signals. If other EVAP or signal-related codes are present, check what they mean first so you do not chase the wrong symptom. Start with the basic system checks, then check for any Service Bulletins or PCM flash updates that apply to this fault. If one applies, do that first, leak test the system afterward, and then continue into the verification routine.
Monitor gates and scan tool verification
Before judging the EVAP test, understand how this monitor is gated. 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. There is a 12 minute delay time where the PCM ignores ESIM Switch input. On the engine-off side, the event can reach a maximum time of 17.5 hours without an ESIM Switch closure, and the accumulation timers are Engine on - 100 minutes and Engine off - 70 hours. For the related EVAP failure logic, vacuum that cannot be created below -250 Pa within a calibrated time matters. The ESIM relief valves regulate around approximately 1” H2O and -2” H2O, shown as 250Pa and -500Pa, and the ESIM switch closes between (-187Pa) and (-250Pa). The ESIM signal may be a 12.0 volt or 5.0 volt signal, with variation between 5.0 and 12.0 volts. Now make sure the vehicle is inside the monitor gates for this path: ambient temperature between 4°C and 35°C, or 39°F and 95°F, fuel level between 12% and 88%, and elevation below 8000 feet. For best test results, the fuel tank should have less than 95% of fuel tank capacity. Next, turn the ignition on, run the Small Leak Verification Test with the scan tool, follow the screen prompts, and document each phase result. If the routine passes, the system may be sealed at that moment; compare the data to the manual phase expectations, and if it is functioning properly, do not make a repair attempt. If it fails, or if the routine is not available or will not run, move into the manual EVAP evaluation.
Manual evaluation, phases one through three
For the manual evaluation, watch and document Purge Duty Cycle %, ESIM Switch State, and Fuel Tank Pressure in Pa through the five phases. Remember, the Fuel Tank Pressure Sensor is useful for diagnosis, but the PCM uses the ESIM switch for leak detection. Also keep temperature in mind: extreme temperature changes can make a leak hard to see, or make a sealed system look like it is leaking. In phase one, vent the system to atmosphere with the ignition on. You can remove the gas cap, open the capless filler, or command the purge solenoid for one minute. The ESIM switch should be open, and the FTP sensor should read near zero. Whatever FTP reads while vented becomes your zero reference. If the ESIM switch reads closed while vented, think short to ground on the ESIM signal, a stuck-closed ESIM switch, or, if you used purge to vent it, a purge solenoid that did not open. Phase two is ignition on, engine off, system closed, and monitor FTP for 2-3 minutes. The pressure should slowly move positive or negative. If it stays steady, keep testing because it could be a leak or just a very stable temperature condition. If it changes more than 200 Pa in 1 minute, the system is too unstable to test accurately. Phase three is right after engine start, while purge is off. Capture ESIM state and FTP within 5-10 seconds. A small vacuum is expected, typically between approximately -25 and -50 Pa. If vacuum is created instantly near or below -500 PA, suspect purge leakage.
Manual evaluation, phases four and five
In phase four, let purge become active long enough to build and stabilize maximum vacuum, then shut the engine off immediately after maximum vacuum is achieved. The recommended approach is to record phase three, turn the engine off, run the Purge Vapors System Test, then return to data display after vacuum is created. FTP should drop quickly to approximately -600 Pa, and the ESIM switch should change to closed. If pressure drops as expected but the ESIM switch does not close, look at a stuck-open switch or an open in the ESIM signal or ground circuit. If the ESIM switch closes but FTP changes very little or not at all, look for a restriction between the canister and FTP sensor or a stuck sensor, and verify the 5-Volt supply at the sensor before condemning it. If the switch does not close and pressure barely changes, think very large leak or purge not opening when actuated. If the vacuum is 2 to 3 times the expected reading, the canister vent hose, fresh air filter, or ESIM vacuum vent valve may be restricted, and the vehicle may also be hard to refuel. In phase five, once maximum vacuum is created and stable, turn the engine off and watch FTP and ESIM state for another 3-4 minutes. FTP should return quickly to the vacuum relief regulation point, approximately -500 Pa, then stabilize. Vacuum should stay below approximately -250 Pa, and the ESIM switch should remain closed. If pressure rises quickly near zero or above -250 Pa and the ESIM switch opens during that 3-4 minute window, treat it as a leak and move into leak detection. If every phase looked correct, the system is most likely not leaking at that time. Possible false-failure causes include software concerns, debris that temporarily held a purge solenoid or ESIM relief valve open and then cleared, or the ESIM not mounted correctly with the switch at the 3 o’clock position.
Whole-system leak check option
Once the manual data points to a leak, choose your leak-check method. One option is to test the entire EVAP system as a whole. Use Kit, EELD And Accessory 8404C. Connect the red lead to battery positive, the black lead to battery negative, connect shop air, set the smoke and air control to AIR, start airflow with the remote button, block the AIR supply tip while pressing the remote button, and calibrate the flow meter if needed. Then connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip to the adapter, activate airflow, and compare the indicator ball to the red flag. Depending on fuel level and venting configuration, it can take several minutes to fill the system. If the ball drops to the bottom of the flow meter or below the red flag, the system is sealed through that test path, and the leak indication points toward the vent valves inside the ESIM. On a capless system that failed the small leak test but passed the pressure test, verify the filler neck is not leaking and go to the fuel tank side check before replacing the ESIM. If the vehicle has a filler cap, replace the ESIM as specified for the vehicle, then verify the repair by running the leak evaluation again. If the ball stays above the red flag, the leak is elsewhere in the system. Use smoke, a hydrocarbon sniffer, or a bubble test to find it. To check for an internal purge solenoid 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, replace the purge solenoid, then run the leak evaluation again to verify the repair.
Split-system leak check and fuel tank side
The other option is to split the EVAP system at the charcoal canister. Remove the canister tube from the charcoal canister, attach a hand vacuum pump to the canister fitting, and pump it until the ESIM switch closes. Then monitor the ESIM switch with the scan tool for up to 10 minutes. If the ESIM switch remains closed for a minimum of 5 minutes, the leak is on the fuel tank side. For the fuel tank side leak check, use Kit, EELD And Accessory 8404C, connect power and shop air, set the tool to Smoke, attach the black hose to the canister tube, and fill the fuel tank side with smoke. Then find and repair the leak using smoke, a hydrocarbon sniffer, or a bubble test. For a purge solenoid internal leak, 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. After the repair, run the leak evaluation again to verify it.
Fresh air side leak check
If the ESIM switch does not stay closed for a minimum of 5 minutes during the split-system test, the leak is on the fresh air, or canister, side. For the fresh air side leak check, use Kit, EELD And Accessory 8404C. Connect power and shop air, set the control to AIR, start airflow with the remote, block the AIR supply tip while pressing the remote, and calibrate the flow meter if needed. Connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip, activate airflow, and compare the indicator ball to the red flag. If the ball drops to the bottom of the flow meter or below the red flag, the leak is coming from the vent valves inside the ESIM, so replace the ESIM as specified for the vehicle. If the ball stays above the red flag, the leak is somewhere else in the system. Use smoke, a hydrocarbon sniffer, or a bubble test. Also check the purge solenoid for internal leakage the same way: remove the manifold hose, fill the system with smoke, and look for smoke coming through the purge solenoid. If smoke is present, replace the purge solenoid. Then run the leak evaluation again to verify the repair.
Verification and takeaway
Keep the verification separate from the leak search. After any confirmed repair, verify the repair and confirm the code stays gone by running the leak evaluation again. The takeaway on P0455 is simple: do not jump straight to parts. Prove the monitor conditions, compare the ESIM and FTP behavior through the phases, then use the EELD result to decide whether the leak is on the tank side, fresh air side, ESIM vent valves, purge path, or somewhere else in the plumbing. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0455 can often be diagnosed by proving the test conditions, comparing commanded EVAP behavior to sensor and switch response, and then isolating which side of the system cannot hold pressure or vacuum
For more guided automotive diagnostics, visit STEP Diagnostics.
