What this code means
P0455 may mean the PCM sees a large leak or fast vacuum loss in the EVAP system during its leak check.
What the vehicle may do
- The MIL may be on.
- The vehicle may drive normally because this is often an emissions-system fault rather than a drivability fault.
- Fuel odor can be possible if the EVAP system is not sealed.
Possible fault areas
- EVAP plumbing may be leaking.
- The charcoal canister may be involved.
- The fuel tank or fuel pump seal area may be involved.
- The ESIM switch, wiring, mounting seal, or internal check valves may be involved.
- The purge solenoid may be leaking internally.
Diagnostic path
Opening context
On this 2019 to 2024 Ram 1500DT with the 5.7 gas engine, P0455 is the large EVAP leak fault. In plain terms, the PCM may be seeing the fuel vapor system lose vacuum too fast during its leak check. The truck may drive normally, but the MIL can be on, and fuel odor may be possible if the system is not sealed. The possible fault area can be anywhere in the EVAP sealing path: plumbing, canister, fuel tank or pump seal area, ESIM mounting or internal valves, ESIM switch or wiring, or a purge solenoid that is leaking. Start with the basic system checks, then work this as a leak and signal confirmation problem, not as a parts-swap problem.
How the fault sets
This monitor is gated by operating conditions, so do not chase the code until the vehicle can reproduce the operating conditions. The monitor gate includes ambient temperature between 4°C and 35°C (39°F and 95°F), fuel level between 12% and 88%, and elevation below 8000 feet. In this strategy, a valid small leak event 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, and the event can run after a maximum time of 17.5 hours without an ESIM Switch closure. The accumulation fail timer thresholds are engine on - 100 minutes, and engine off - 70 hours. For the broader EVAP logic, a failure can be tied to vacuum cannot be created below -250 Pa within a calibrated time. For P0455, the large leak fault sets when the PCM runs an intrusive EVAP test and the ESIM switch opens before the calibrated time. Temperature changes matter here. A fast temperature swing can temporarily hide a leak by creating vacuum too quickly, or it can make a sealed system look like it is leaking because vapor pressure decays the vacuum too fast.
Check bulletins and flash updates first
Before getting deep into testing, check for any applicable service bulletins or PCM flash updates for this fault. If one applies, handle that first, then leak test the EVAP system to make sure it is sealed. If nothing applies, move on to the leak verification routine.
Run the scan tool verification routine
Turn the ignition on and run the Small Leak Verification Test with the scan tool. Follow the scan tool prompts and document the results from each phase. If the routine passes, the system may be sealed right now; compare the phase results to the expected patterns before making any repair. If the system is functioning properly, do not repair anything. If the routine fails, use those phase results to guide the next step. If the routine is not available or will not run, go straight into the manual EVAP evaluation. One important detail: this routine makes its decision from the fuel tank pressure sensor reading. The ESIM switch is still useful for diagnosis, but it is not factored into that scan tool routine decision.
Manual EVAP evaluation
For the manual evaluation, the fuel tank should have less than 95% of Fuel Tank capacity for best results. Watch and record Purge Duty Cycle %, ESIM Switch State, and Fuel Tank Pressure: Pa. Keep in mind these results are subjective, not absolute, and they can move around with tank size, fuel volume, barometric pressure, ambient temperature, and fuel temperature. Phase 1 is venting the system and recording ESIM and FTP data. If needed, the system can be vented by removing the gas cap, opening the capless filler, or actuating the purge solenoid for one minute with the scan tool. Phase 2 is ignition on, engine off, monitoring ESIM state and FTP data for 2-3 minutes. A change of more than 200 Pa in 1 minute would indicate the system is too unstable to accurately test. Phase 3 is starting the engine and recording ESIM state and FTP within 5-10 seconds after start, before purge becomes active; a small amount of vacuum is typically between approximately -25 and -50 Pa. Phase 4 is letting purge become active just long enough to create maximum vacuum, which should reach approximately -600 Pa, then recording ESIM and FTP. Phase 5 is turning the engine off and watching ESIM and FTP for an additional 3-4 minutes. The FTP reading should quickly return to the vacuum relief regulation point, approximately -500 Pa, and stabilize.
Read the manual evaluation results
Use the phase data to separate a real leak from a control or signal problem. The ESIM switch closes when system vacuum reaches between (-187Pa) and (-250Pa), and the ESIM Signal will typically be a 12.0 volt or 5.0 volt signal depending on the vehicle. The voltage signals can vary between vehicles and may be somewhere between 5.0 and 12.0 volts, so know what you are looking at before calling the circuit wrong. If the ESIM switch reads closed while the system is vented, think about the ESIM signal being grounded, the switch stuck closed, or purge not opening if it was commanded and FTP did not change. In Phase 2, a steady pressure value can mean a leak is present, or that temperature was too stable to move the pressure; keep testing before calling it. A very rapid pressure change means the result is invalid because the temperature change is too large. In Phase 3, if vacuum appears instantly after engine start near or below the ESIM regulation point of -500 PA, the purge solenoid is leaking. In Phase 4, if FTP drops but ESIM does not close, suspect an ESIM switch or circuit issue. If ESIM closes but FTP 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 ESIM nor FTP responds, that points toward a very large leak or a purge solenoid that is not opening when commanded. If vacuum is 2 to 3 times the expected reading, look for a plugged canister vent hose, plugged fresh air filter, or ESIM vacuum vent valve stuck closed; that condition can also show up as hard refueling. For the large leak path, the key Phase 5 result is this: if fuel tank pressure rises quickly near zero or above -250 Pa and the ESIM switch opens within 3-4 minutes, the system has a leak and you move into leak checking. If every phase looks as expected, the system is most likely not leaking at this time.
Choose the leak check approach
Once the manual evaluation points to a leak, choose how you want to attack it. You can leak test the entire EVAP system as one assembly, or you can split the system at the charcoal canister and determine whether the leak is on the fuel tank side or the fresh air canister side.
Whole-system EELD test
For the whole-system method, use Kit, EELD And Accessory 8404C. Connect the red EELD power lead to Battery positive and the black ground lead to Battery negative. Connect shop air to the EELD, set the smoke and air control switch to AIR, and press the remote smoke and air start button. Block the tester AIR supply tip while pressing the remote button. If the indicator ball is not resting on the bottom of the air flow meter, align the red flag with the ball. Then connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip to the adapter, and activate AIR flow. Compare the flow meter 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 vent valves inside the ESIM, because the rest of the system is not leaking; replace the ESIM and run the intrusive leak evaluation again. If the ball stays above the red flag, the leak is elsewhere in the system. Find it with smoke, a hydrocarbon sniffer, or a bubble test, then repair or replace the leaking component. 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 through the Purge Solenoid. If smoke is present, replace the Purge Solenoid, then run the intrusive leak evaluation again.
Split the system at the canister
If you prefer to split the system, remove the canister tube that connects to the fuel tank from the charcoal canister. Attach a hand vacuum pump to the fitting on the canister and pump it until the ESIM switch closes. With the scan tool, monitor ESIM switch state 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 of the system. If it does not remain closed for a minimum of 5 minutes, the leak is on the fresh air canister side.
Fuel tank side leak detection
For the fuel tank side, use Kit, EELD And Accessory 8404C. Connect the red lead to Battery positive and the black lead to Battery negative, connect shop air, and set the smoke and air control switch to Smoke. Attach the black hose to the canister tube, then press the remote button to fill the fuel tank side of the system with smoke. Use smoke, a hydrocarbon sniffer, or a bubble test to find the leak. Repair or replace the leaking component. For an internal purge solenoid leak check, 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 intrusive leak evaluation again.
Fresh air side leak detection
For the fresh air side, use Kit, EELD And Accessory 8404C. Connect power, ground, and shop air the same way. Set the smoke and air control switch to AIR, activate the tester, and block the AIR supply tip while the remote button is pressed. If the indicator ball is not resting on the bottom of the air flow meter, align the red flag with the ball. Connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip to the adapter, and activate AIR flow. If the ball drops to the bottom of the air flow meter or below the red flag, the leak is coming from the vent valves inside the ESIM; replace the ESIM. If the ball stays above the red flag, the leak is elsewhere on that side of the system. Use smoke, a hydrocarbon sniffer, or a bubble test, then repair or replace the leaking component. Check the purge solenoid the same way: remove the Manifold Hose, fill the system with smoke, and replace the Purge Solenoid only if smoke is present through it. Then run the intrusive leak evaluation again.
Verify and wrap up
Keep verification separate from the leak-finding work. After any repair, run the intrusive leak evaluation again, confirm the system stays sealed, and confirm P0455 stays gone. The takeaway is simple: prove the leak first, use ESIM and FTP data to avoid false calls, then smoke or airflow-test only the section the data points you toward. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0455 is best approached by confirming the leak condition, separating the system logically, and repairing only what the test results support.
For more guided automotive diagnostics, visit STEP Diagnostics.
