P0456 Evap System Small leak

P0456 Evap System Small leak - If no ESIM switch closures were recorded during an entire a accumulative increment, it is determined that a small leak is present. Default action the MIL is illuminate on the firs trip that the diagnostic fails, the MIL will be turned off on the third consecutive trip that the diagnostic passes.

P0456 Evap System Small leak

Evaporative System Overview P0456 code -the Powertrain Control Module (PCM) monitors the Evaporative Emission System operation. The two main areas being monitored are the integrity of the system against leaks and the ability of the system to get fuel vapor from the canister to the Intake Manifold. The basic strategy used is that in a sealed system, pressure will naturally increase or decrease in relation to temperature. As temperature increases, so does pressure inside the system. And conversely, as temperature decreases, pressure in the system will decrease as well and will eventually turn into a vacuum if no leaks are present.

P0456 Evap System Small leak

Even the smallest of leaks can be accurately detected in this manner. The ESIM has multiple functions. There are two weighted seals that keep the system normally closed from the atmosphere. The weighted seals are used to maintain the system pressure between +1 inch of water and -2 inches of water. Anytime (engine-on or engine-off) that pressure or vacuum reaches these thresholds, the weights will lift and provide relief.
There is also a vacuum actuated switch that closes when the vacuum reaches a calibrated value. This is beneficial because the induced vacuum during a subsequent declining temperature will achieve the switch closed (pass threshold) sooner than if the tank had to decay from a higher built up pressure.

Esim switch stuck closed monitor - at ignition off, the state of the ESIM switch is evaluated. If the switch is open, a pass flag will set so the PCM power down process can complete. If the switch is closed, the PCM will wait a calibrated delay time and open the Purge Solenoid.
In a normally functioning system, this will relieve the vacuum in the Fuel Tank by drawing in air from the atmosphere from the Intake Manifold. When the switch opens, a pass flag is set and the PCM will power down. If the ESIM switch does not open, after a calibrated time, an error is detected and a switch stuck closed failure event is set. Two consecutive failed events will mature a fault.

Small leak monitor - this is an accumulative monitor and the data from each valid event is recorded and added to the previously recorded events. The PCM timer records the engine on/drive cycle and engine off time for each small leak monitor event. For an event to be valid the PCM must see;

1. An engine on/drive cycle for a minimum of 2 minutes.
The engine on timer is clipped to a maximum of 26 minutes on any given trip.

2. And, when the engine is shut down, an engine off timer starts. There is a 12 minute delay time in which the PCM will ignore ESIM switch input. The engine off timer period will continue to count one of the three conditions exist :
  • The engine is started without a switch closure during the event.
At the next key on cycle a determination is made as to whether the event was valid and the information is kept.
  • An ESIM switch closed input is received after the 12 minute delay during the event.
If the switch closed input is received, the PCM records that the switch has closed and stores the engine shut down time.
  • After a maximum of 1051 minutes without an ESIM switch closure during the event.

This monitor will increment the accumulation fail timers until both have reached a calibrated threshold (Engine on - 100 minutes and Engine off - 4200 minutes).
When the monitor records a valid switch closure (small leak passing event) the fail timers are reset. Separate timers are running in the background to verify that this monitor is completing on a regular basis.

Leak size determination - if the PCM did not see an ESIM Switch closed signal during the previous ignition off cycle, the event was valid, and there is a cold start, an intrusive leak test is run to determine if a large leak.
Shortly after the vehicle has achieved closed loop fueling during the next drive cycle, and when the enable conditions are met, the Purge Solenoid is opened to create a vacuum in the evaporative system to a calibrated vacuum point that is beyond the ESIM Switch closing threshold. The pass/fail time will vary based on the total fuel volume at the time of the test.

If the switch does not close at all during purging, because of a switch that is stuck open or vacuum cannot be created below 1.0 inch of water within a calibrated time threshold, it is determined to be a general evaporative system failure (P0440).

If vacuum is created and the switch has closed, the PCM stops purge and monitors the switch closure time. If the switch opens before a calibrated time, a large leak is present. Two consecutive failure events will mature a fault (P0455).

If vacuum is created and the switch has closed, the PCM stops purge and monitors the switch closure time. If the switch stays closed longer than a maximum calibrated time before opening, it is determined that a large leak is not present and the Small Leak Monitor will continue to run until the accumulative monitor increments. If no ESIM Switch closures were recorded during the entire accumulated timers, it is determined that a small leak is present (P0456).

Monitored code P0456 Evap System Small leak

  • After the ignition os off for a calibrated time.
  • Fuel level less than 88%.
  • Ambient temperature between 4°C and 43°C (39°F and 109°F).
  • Elevation is below 8000 feet.


Possible causes:
  • ESIM internal check valves leaking.
  • Purge solenoid leaking.
  • Small evap system leak.

Diagnose code P0456 Evap System Small leak

Step 1. Check for an active condition
Before proceeding with this procedure, perform any service bulletin or PCM flas updates that relate to this fault code.

Keep lit cigarettes, sparks, flames, and other ignition sources away from the test area to prevent the ignition of explosive gases. Keep the test area well ventilated. Failure to do so may result in possible serious or fatal injury.

The fuel tank should have less than 95% of fuel tank capacity to properly test the evap system.

Connect the red power lead of the EELD to the battery positive terminal and the black ground lead to battery negative terminal. Connect shop air to the EELD. Set the smoke/air control switch to air. Insert the testers air supply tip (clear hose) into the appropriate calibration orifice on the tester control panel (based on DTC leak size). Press the remote smoke/air start botton. Position the red flag on the air flow meter so it is aligned with the indicator ball. When the calibration is complete, release the remote botton. The EELD flow meter is now calibrated in liters per minute to the size leak indicated by the DTC set in the PCM.

If not connecting the EELD to the ESIM, the vent must be capped or plugged. The pressure developed by the EELD will over come the weights in the ESIM, causing the vent seal to open allowing the system to vent. This could lead to a false failure condition.
Connect the air supply hose from the EELD to the adafter. Press the remote botton to activate air flow.
Depending on the vehicles fuel level or vehicle venting configuration, it can take up to five minutes to fill the system.
Compare the flow meter indicator ball reading to the red flag. ABOVE the red flag indicates a leak present. BELOW the red falg indicates a sealed system.

Did the small leak test pass or fail?

PASSED, go to step 2.

FAILED, go to step 3.

Step 2. Evap system inspection
Temperature changes during testing can yield poor results. For best results, allow the vehicle to archive ambient temperature and retest for leaks.
It is possible that the fuel filter cap (id applicable) or capless fuel filter assembly was previously leaking.
Perform a visual inspection of the entire evaporative emission system for any of the following conditions but not limited to:
  • Damaged seal points on the fuel filter cap (if applicable) or capless fuel filter assembly.
  • Small holes or cracks.
  • Loose seal points.
  • Damaged components.
  • Incorrect routing of hoses and tubes.
Were any problems found?

YES, repair as necessary.
NO, replace the ESIM.

Step 3. Evaporative emission leak detection
A thorough visual inspection of the Evap system hoses, tubes, and connections may save time in your diagnosis. Look for any physical damage or signs of wetness at connections. The strong smell of fuel vapors may aid diagnosis also.

Remove the air supply hose from the Adafter. Connect the smoke supply tip (black hose) to the adafter. Set the smoke/air control switch to smoke. The flow meter indicator ball will not move in the smoke mode. Press the remote smoke/air start botton. Make sure that smoke has failed the evap system by continuing to press the remote amoke/air start botton, remove the vehicle fuel cap (if applicable) or open the flap (capless), and wait for the smoke to exit. Once smoke is indicated reinstall the fuel cap or close the flap.

For optimal performance, introduce smoke into the system for an additional 60 seconds, continue introducing smoke at 15 second intervals, as necessary. The exiting smoke deposit a residual fluid that is either bright green, yellow or purple in color when viewed with a UV light.

Carefully inspect the vent side of the Evap Canister. Due to the filtering system in the canister the smoke may not be as thick. Introducing smoke into the filtered side of the canister may assist in locating the leak.

Select the appropriate response from the list below:

A leak was found at the fuel cap (if applicable) or fuel filler tube assembly, perform the appropriate repair by replacing the fuel filler tube assembly and/or the fuel cap (if applicable).

A leak was found in the evap system, if the leak is at a hose connection, remove the hose then reconnect the hose and check for a leak again. All other leaks, repair as necessary.

No leaks were detected, go to step 4.

Step 4. Purge solenoid
Disconnect the vacuum hose that connects to the intake manifold at the purge solenoid.
After disconnecting the purge solenoid vacuum connection, inspect the line solenoid for signs or contamination. Check for smoke coming through the purge solenoid. The solenoid should be sealed with the ignition off.

Smoke is leaking passed the purge solenoid?

YES, replace the purge solenoid.

NO, If the system failed the small leak test in step one, a leak is present but was not found during testing. Perform system leak test found in step three over again. While performing test verify all system connection and seal points. Inspect system lines for small cracks that may open with line movement.

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