What this code means
P0455 can indicate a very large EVAP leak when fuel tank pressure after engine stop is outside its specified value.
P0455 concerns a very large leak condition in the evaporative-emission system. In the condition described by this procedure, fuel tank pressure after the engine stops is outside its specified value. The diagnosis therefore connects the stored leak code with pressure information and the listed system inspections.
The EVAP system is examined through several named areas and checks. The procedure distinguishes its initial conditions, functional operations and individual component inspections. Keeping those stages separate allows the pressure result and the component findings to support the appropriate branch.
What the vehicle may do
- Tank pressure after engine stop may be outside its specified range.
Possible fault areas
- Possible faults include the EVAP vent hose, purge valve, and its integrated non-return valves.
- The purge line, canister, FTP sensor, vent shut valve, and O-rings may have connection problems or damage.
- The fuel fill pipe, vapor recirculation tube, main flap unit, or fuel tank may also be involved.
Begin with the specified preliminary actions. Then follow the operating or confirmation sequence before applying the individual inspection results. The HDS function paths identify which data or commanded operation belongs to each stage.
Some checks use a pressure reading under a defined setup, while other checks examine operation or condition of a particular part. Preserve those different result types. The conclusion for a hose, valve, canister or sensor belongs to its corresponding check and cannot be supplied by a result from another setup.
Diagnostic path
Understand the stored condition
P0455 means Evaporative Emission (EVAP) System Very Large Leak Detected. The PCM stores this code when fuel tank pressure after engine stop is outside its specified value.
Prepare for the checks
The fuel system is designed for specified maximum vacuum and pressure conditions. Do not go beyond the vacuum and pressure tests described here. Excessive pressure or vacuum can damage EVAP components or cause eventual fuel tank failure. Use the Vacuum Pump/Gauge, 0-30 inHg Snap-on YA4000B or equivalent, commercially available. Fresh fuel has higher volatility and creates greater pressure or vacuum. The best testing condition is less than a full tank of fresh fuel.
If possible, add 1 gallon of fresh fuel just before starting these checks to help with leak detection. Do this only if that amount will not fill the tank.
Check whether the failure is duplicated
Turn the vehicle to the ON mode. On the HDS, select PGM-FI ＞ Function Test ＞ EVAP TEST ＞ FUNCTION TEST. If the test result is not OK, the failure is duplicated. The HDS also lists FTP Sensor Voltage under PGM-FI ＞ Data List.
Check the vent hose
With the EVAP canister vent hose disconnected, check it for blockage or restriction. A normal hose has no blockage or restriction. If this check is abnormal, there is a problem with the vent hose.
This inspection isolates the named part using the connector or hose arrangement stated in the procedure. The expected reading or operation criterion belongs to that arrangement. Record the result before moving on so that the later fault-area conclusion remains tied to the part actually being evaluated.
Check whether the purge valve is stuck open
Remove the EVAP canister purge valve, but leave its connector connected. For these checks, use the vacuum pump/gauge, 0-30 inHg, to apply pressure or vacuum to the valve port. All purge valve inspection results must be within specification for a normal result. First, apply pressure to one side port as shown. The pressure should hold. This is the normal result when checking for a valve stuck open.
Check whether the purge valve is stuck closed
On the HDS, select PGM-FI ＞ Function Test ＞ EVAP TEST ＞ SINGLE SOLENOID > PCS(CPV) ON. Apply pressure to one side port as shown. The pressure should not hold. That is the normal result for the stuck-closed check.
Check for leakage and a stuck-open non-return valve
This troubleshooting requires the purge valve leak and non-return valve stuck-open inspection. Before you begin, complete the purge valve stuck-closed check and confirm that its result is within specification. Select the HDS [PCS(CPV) ON]. Apply vacuum to one side port as shown. The vacuum should hold for a normal result.
Check non-return valve A
Next, check non-return valve A on the intake manifold side for a stuck-closed condition. Select the HDS [PCS(CPV) ON]. Apply vacuum to one side port as shown. The vacuum should not hold. That is the normal result for this check.
Check non-return valve B
Now check non-return valve B on the turbocharger side for a stuck-closed condition. Select the HDS [PCS(CPV) ON]. Apply vacuum to one side port as shown. The vacuum should not hold. That is the normal result for this check. If any purge valve inspection is abnormal, there is a problem with the purge valve.
Look over the purge line and connected parts
Check the EVAP canister purge line between the purge valve and the EVAP canister. Look for poor connections or damage. Also check the canister, FTP sensor, EVAP canister vent shut valve, and O-rings for damage. Normal connections are OK, with no damage to the checked parts. If this check is abnormal, there is a problem with parts on the purge line.
Check whether the purge line holds vacuum
Do not exceed the specified vacuum during this check. Too much vacuum can damage the FTP sensor. Disconnect the vent hose (A) and fuel vent tube (B) from the canister (C). Plug each port (D). In the engine compartment, disconnect the vacuum hose, or purge line (E), from the purge valve (F). Connect the vacuum pump/gauge, 0-30 inHg, to that vacuum hose as shown. Turn the vehicle to the ON mode.
Apply vacuum until the HDS [FTP Sensor Voltage] reads 1.90 V (-0.59 inHg, -15.1 mmHg). Watch the HDS [FTP Sensor Voltage] for 1 minute. A normal reading does not increase more than 0.2 V (0.1 inHg, 2.5 mmHg). If this check is abnormal, there is a problem with parts on the purge line.
Check the vent shut valve
The purge line must be normal before this check. Do not exceed the specified vacuum, because too much can damage the FTP sensor. Disconnect the fuel vent tube (A) from the canister (B), and plug the port (C). In the engine compartment, disconnect the vacuum hose, or purge line (D), from the purge valve (E). Connect the vacuum pump/gauge, 0-30 inHg, to that vacuum hose as shown. Turn the vehicle to the ON mode.
On the HDS, select PGM-FI ＞ Function Test ＞ EVAP TEST ＞ SINGLE SOLENOID > CVS ON. Apply vacuum until the HDS [FTP Sensor Voltage] reads 1.90 V (-0.59 inHg, -15.1 mmHg). Watch the HDS [FTP Sensor Voltage] for 1 minute. A normal reading does not increase more than 0.2 V (0.1 inHg, 2.5 mmHg). If this check is abnormal, there is a problem with the vent shut valve.
Check the fill pipe and vapor tube
Check the fuel fill pipe and fuel tank vapor recirculation tube for poor connections or damage. For a normal result, the connections should be OK and neither part should have damage. If the result is abnormal, it points to a problem with the fill pipe, vapor recirculation tube, or both.
Check the main flap unit
Check that the shut-off valve (A) is closed. Inspect its flap seal (B) and the valve's mating surface for missing material or damage. A normal result has the valve closed, with no missing or damaged seals. If this check is abnormal, there is a problem with the main flap unit.
When the other checks are normal
If all the other inspection items are normal, the remaining fuel tank is determined to be the cause. Under that condition, the result points to a problem with the fuel tank.
Final check
The checks can identify problems in EVAP components; the fuel tank is the stated cause only when the other inspection items are normal.
Bring the findings together in the order they were obtained: initial code and operating conditions, confirmation, and each component inspection. A normal reading under one hose or connector arrangement does not automatically describe a different arrangement. Preserve each result with its setup and follow the specific conditional conclusion written for it.
