P0455: EVAP System Large Leak

What this code means

P0455 generally means the EVAP system may not be holding vacuum or pressure the way the PCM expects, and the PCM may interpret that as a large leak.

What the vehicle may do

The MIL may illuminate.
The vehicle can often drive normally with no obvious drivability symptom.
Refueling difficulty may be possible if the fresh air side is restricted.

Possible fault areas

EVAP plumbing may be leaking.
The charcoal canister area may be involved.
The fuel tank or fuel pump seal area may be involved.
The ESIM, its seal, mounting, valves, or wiring may be involved.
The purge solenoid may be leaking.

Diagnostic path

Opening context

On this 2019 to 2024 Ram 1500 Classic with the 5.7 HEMI, P0455 means the PCM saw the EVAP system act like it has a large leak. The truck may run normally, but the MIL can illuminate. Broadly, this can involve EVAP plumbing, the charcoal canister area, the fuel tank or fuel pump seal area, ESIM sealing or wiring, ESIM mounting, internal ESIM valves, or a purge solenoid that is leaking. If other EVAP or signal-related codes are present, check what they mean first, then stay focused on proving whether this system is actually leaking right now.

How the code sets and when to trust the test

For P0455, the PCM runs an intrusive EVAP test to judge leak size. During that test, the ESIM switch opened before the calibrated time, so the PCM interpreted that as a large leak. Treat the operating conditions as monitor gates: this runs on a cold start after the small leak test failed during the last valid key-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. In the background logic, the small leak monitor is looking for an engine on/drive cycle for a minimum of 2-5 minutes. The Engine on timer is clipped to a maximum of 26 minutes on any given trip, and there is a 12 minute delay time where the PCM ignores ESIM Switch input. The logic also looks at an engine-off event after a maximum time of 17.5 hours without an ESIM Switch closure, with fail accumulation called out as Engine on - 100 minutes and Engine off - 70 hours. Temperature matters here. A fast temperature swing can hide a leak by creating vacuum too quickly, or make a sealed system look like it is leaking because vapor build-up decays vacuum too quickly.

System behavior before testing

Before you get deep into the leak hunt, understand what the PCM and ESIM are doing. A general EVAP failure pattern is that vacuum cannot be created below -250 Pa within a calibrated time. When system vacuum reaches between (-187Pa) and (-250Pa), it acts on the diaphragm and closes the vacuum switch. On the electrical side, the ESIM Signal will typically be a 12.0 volt or 5.0 volt signal depending on the vehicle, and voltage signals can vary between vehicles and may be somewhere between 5.0 and 12.0 volts. That is why both the sealing side and the switch signal side matter on this code.

Start with basic checks and calibration information

Start with the basic system checks. Then check for any applicable service bulletins or PCM flash updates related to this fault. If one applies, perform it, then make sure the EVAP system is not leaking by leak testing it before moving on. If nothing applies, continue into the verification routine.

Run the scan tool verification routine

Next, turn the ignition on and run the Small Leak Verification Test with the scan tool. Follow the on-screen prompts and document the results from each phase. If the routine passes, the system may be sealed at that moment, so compare the recorded data to the manual evaluation pattern before attempting any repair. If the system is functioning properly, do not repair anything. If the routine fails, use the manual evaluation data to decide where the failure pattern points. If the routine is not available or will not run, go straight to the manual evaluation. Remember, this routine is based only on the FTP Sensor pressure reading. The ESIM Switch state is not part of that routine’s decision, even though the PCM uses the ESIM switch for leak detection.

Set up the manual EVAP evaluation

For the manual evaluation, watch Purge Duty Cycle %, ESIM Switch State, and Fuel Tank Pressure: Pa on the scan tool. For best results, the fuel tank should have less than 95% of Fuel Tank capacity. Keep in mind these readings are not absolute. Tank size, fuel volume, barometric pressure, ambient temperature, and fuel temperature can all affect what you see. Treat the EVAP components and wiring as a system, not just as one code name. Also remember, the PCM does not use the Fuel Tank Pressure Sensor to decide the leak, but that sensor is useful for diagnosing the system.

Manual evaluation phases one through three

Run the five manual phases in order. First, vent the system and record ESIM state and FTP data. The ESIM switch should be open and the FTP sensor should read near zero. If the ESIM switch reads closed, think about an ESIM signal short to ground, a switch stuck closed, or a purge solenoid that did not open when actuated. If you actuate the purge solenoid for venting, the time called out is one minute. Second, monitor and document ESIM state and FTP data for 2-3 minutes. A sealed system should slowly build pressure or vacuum as temperature changes. More than a 200 Pa change in 1 minute means the system is too unstable to test accurately. A steady value can mean a leak, or simply temperature conditions that are too stable, so keep testing. A very rapid change points to too much temperature change and an invalid result. Third, start the engine and record the data within 5-10 seconds after the engine starts while purge is still off. You should see a small vacuum from fuel being pulled from the tank, typically between approximately -25 and -50 Pa. If vacuum appears immediately near or below the ESIM regulation point (-500 PA), suspect a purge solenoid leak pattern.

Manual evaluation phases four and five

Fourth, let purge become active only long enough to create maximum vacuum, then record ESIM state and FTP data. The FTP reading should drop quickly to approximately -600 Pa and the ESIM switch should change to closed. If pressure drops correctly but the ESIM switch does not close, look at a switch stuck open or an open 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 faulty stuck sensor, and verify the 5-Volt supply before condemning the sensor. If neither the switch nor the pressure reacts, think very large leak or purge not opening when commanded. If vacuum is 2 to 3 times the expected reading, look for a plugged canister vent hose or fresh air filter, or an ESIM vacuum vent valve stuck closed; that pattern can also go along with refueling difficulty. Fifth, turn the engine off and monitor ESIM state and FTP data for 3-4 minutes. The FTP sensor should quickly return to the vacuum relief regulation point, approximately -500 Pa, and stabilize. Vacuum should stay below approximately -250 Pa, and the ESIM switch should remain closed for the additional 3-4 minutes of monitoring. If the FTP reading rises quickly near zero or above -250 Pa and the ESIM switch opens within the 3-4 minutes, the system has a leak and you move into leak location testing. If all five phases match the expected results, the system is most likely not leaking at this time. Possible false-failure causes include software issues, debris in the purge solenoid or ESIM relief valves that has cleared, or the ESIM not mounted correctly with the switch at the 3 o’clock position.

Choose the leak-check path

Once the data says the system is leaking, choose how you want to leak check it. You can test the complete EVAP system as one assembly, or you can split the system at the charcoal canister and test each side. The complete-system path goes into the EELD flow-meter check. The split-system path first decides whether the leak is on the fuel tank side or the fresh air side.

Whole-system EELD check

For the whole-system check, use Kit, EELD And Accessory 8404C. Connect the red power lead to Battery positive and the black ground lead to Battery negative, connect shop air, set the smoke-air control switch to AIR, and start airflow with the remote button. Block the tester AIR supply tip while pressing the remote start button, and if needed, set the red flag on the airflow meter even with the ball. Then connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip to the adapter, and activate airflow. If the EELD is calibrated correctly, the indicator ball should rest at the bottom of the airflow meter when no leak is present. 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 airflow meter or below the red flag, the leak is coming from the vent valves inside the ESIM, so replace the ESIM and repeat the intrusive leak evaluation. If the ball stays above the red flag, the leak is elsewhere in the system. Find and repair the leak using smoke testing, a hydrocarbon sniffer, or a bubble test, then repeat the intrusive leak evaluation.

Split-system decision at the canister

If you split the system, remove the canister tube from the charcoal canister, the tube that connects to the fuel tank on the other end. Attach a hand vacuum pump to the canister fitting and pump it until the ESIM switch closes. Then monitor ESIM switch state 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. If it does not remain closed for a minimum of 5 minutes, the leak is on the fresh air, or canister, side. This split check is aimed at the fresh air side, including ESIM internal valves and seal, the canister, purge solenoid, and the purge tube between the solenoid and canister.

Fuel tank side leak detection

For a fuel tank side leak, use Kit, EELD And Accessory 8404C. Connect power and ground to the battery, connect shop air, set the smoke-air switch to Smoke, attach the black hose to the canister tube, and use the remote button to fill the fuel tank side of the system with smoke. Locate the leak with smoke testing, a hydrocarbon sniffer, or a bubble test, then repair the leak. To check the purge solenoid for an internal leak, remove the manifold hose from the purge solenoid, fill the system with smoke, and watch for smoke coming through the purge solenoid. If smoke comes through the purge solenoid, replace the purge solenoid. After the repair, repeat the intrusive leak evaluation.

Fresh air side leak detection

For a fresh air side leak, use Kit, EELD And Accessory 8404C. Connect the EELD power and ground to the battery, connect shop air, set the control switch to AIR, start airflow, block the AIR supply tip while pressing the remote button, and set the red flag to the ball if needed. Connect service adapter 8404-ADP to the ESIM vent hose, connect the AIR supply tip, and activate airflow. If the ball drops to the bottom of the airflow meter or below the red flag, the leak is coming from the vent valves inside the ESIM, so replace the ESIM. If the ball stays above the red flag, the leak is somewhere else in the system. Find and repair it using smoke testing, a hydrocarbon sniffer, or a bubble test. After leak repair, repeat the intrusive leak evaluation.

Closing takeaway

The key on P0455 is not to guess at parts. Prove the EVAP system is leaking under valid conditions, use ESIM state and FTP data to understand the failure pattern, then use the EELD path to isolate the leak before calling the repair. For more diagnostic training, visit stepdiagnostics.com.