THE P0455 CODE POSSIBLE CAUSES ARE
- Leak at Gas Cap
- Vehicle History and Service Bulletin Investigation
- Visual and Physical Inspection
- Verify Evaporative Emission Leak
- EVAP Purge Solenoid Operation
- Intermittent LDP Monitor Failure
- Evaporative Emission Leak Detection
- Gas Cap
- LDP Component Leak
WHAT ENGINE DIAGRAMS I HAVE IS BELOW WITH DEFINITIONS
On 4.0L 6 cylinder engines, a molded vacuum tube connects manifold vacuum to top
of cylinder head (valve) cover at dash panel end. The vacuum fitting contains a
fixed orifice of a calibrated size. It meters the amount of crankcase vapors
drawn out of the engine.
On 2.5L 4 cylinder engines, a fitting on drivers
side of cylinder head (valve) cover contains the metered orifice. It is
connected to manifold vacuum.
A fresh air supply hose from the air
cleaner is connected to front of cylinder head cover on 4.0L engines. It is
connected to rear of cover on 2.5L engines.
When the engine is operating,
fresh air enters the engine and mixes with crankcase vapors. Manifold vacuum
draws the vapor/air mixture through the fixed orifice and into the intake
manifold. The vapors are then consumed during combustion.
EVAP/PURGE
SOLENOID The duty cycle EVAP canister purge solenoid (DCP) regulates the
rate of vapor flow from the EVAP canister to the intake manifold. The Powertrain
Control Module (PCM) operates the solenoid.
During the cold start warm-up
period and the hot start time delay, the
PCM
does not energize the solenoid. When de-energized, no vapors are purged. The PCM
de-energizes the solenoid during open loop operation.
The engine enters
closed loop operation after it reaches a specified temperature and the time
delay ends. During closed loop operation, the
PCM
cycles (energizes and de-energizes) the solenoid 5 or 10 times per second,
depending upon operating conditions. The PCM varies the vapor flow rate by
changing solenoid pulse width. Pulse width is the amount of time that the
solenoid is energized. The PCM adjusts solenoid pulse width based on engine
operating condition.
FUEL
FILLER CAP The plastic fuel tank filler tube cap is threaded onto
the end of the fuel fill tube Certain models are equipped with a 1/4 turn
cap.
The loss of any fuel or vapor out of fuel filler tube is prevented
by the use of a pressure-vacuum fuel fill cap. Relief valves inside the cap will
release
fuel
tank pressure at predetermined pressures. Fuel tank vacuum will also be
released at predetermined values. This cap must be replaced by a similar unit if
replacement is necessary This is in order for the system to remain
effective.
CAUTION: Remove fill cap before servicing any fuel
system component to relieve tank pressure. If equipped with a California
emissions package and a
Leak
Detection Pump (LDP) , the cap must be tightened securely. If cap is
left loose, a Diagnostic Trouble Code
(DTC) may be set.
LEAK
DETECTION PUMP The Leak Detection Pump (LDP) is used only with
certain emission packages
The LDP is a device used to detect a leak in
the evaporative system.
The pump contains a 3 port solenoid, a pump that
contains a switch, a spring loaded canister vent valve seal, 2 check valves and
a spring/diaphragm.
Immediately after a cold start, engine temperature
between
40 °F and
86 °F , the 3 port solenoid is briefly
energized. This initializes the pump by drawing air into the pump cavity and
also closes the vent seal. During non-test test conditions, the vent seal is
held open by the pump diaphragm assembly which pushes it open at the full travel
position. The vent seal will remain closed while the pump is cycling. This is
due to the operation of the 3 port solenoid which prevents the diaphragm
assembly from reaching full travel. After the brief initialization period, the
solenoid is de-energized, allowing atmospheric pressure to enter the pump
cavity. This permits the spring to drive the diaphragm which forces air out of
the pump cavity and into the vent system. When the solenoid is energized and
de-energized, the cycle is repeated creating flow in typical diaphragm pump
fashion. The pump is controlled in 2 modes:
Pump Mode: The pump is
cycled at a fixed rate to achieve a rapid pressure build in order to shorten the
overall test time.
Test Mode: The Solenoid Is Energized With A
Fixed Duration Pulse. Subsequent fixed pulses occur when the diaphragm reaches
the switch closure point.
The spring in the pump is set so that the
system will achieve an equalized pressure of about
7.5 inches of
water.
When the pump starts, the cycle rate is quite high. As the system
becomes pressurized pump rate drops. If there is no leak the pump will quit. If
there is a leak, the test is terminated at the end of the test mode.
If
there is no leak, the purge monitor is run. If the cycle rate increases due to
the flow through the purge system, the test is passed and the diagnostic is
complete.
The canister vent valve will unseal the system after completion
of the test sequence as the pump diaphragm assembly moves to the full travel
position.
VACUUM LINES A vacuum schematic for emission related
items can be found on the VECI label. Refer to Vehicle Emission Control
Information
(VECI) Label for label location
VAPOR CANISTER The evaporative (
EVAP)
canister is located in the engine compartment on the left inner fender.
A
maintenance free, EVAP canister is used on all vehicles. The EVAP canister is
filled with granules of an activated carbon mixture. Fuel vapors entering the
EVAP canister are absorbed by the charcoal granules.
Fuel
tank pressure vents into the EVAP canister. Fuel vapors are temporarily held
in the canister until they can be drawn into the intake manifold. The duty cycle
EVAP canister purge solenoid allows the EVAP canister to be purged at
predetermined times and at certain engine operating
conditions.
ONE WAY TO CLEAR ENGINE CODES WITH OUT HAVING A DIAGNOSTIC COMPUTER IS UN PLUG THE BATTERY AND LEAVE IT SIT FOR ROUGHLY 20 MINUTE AND REHOOK UP THIS MIGHT CLEAR THE CODES WITH OUT A COMPUTER.. BUT IF THE PROBLEM ISN'T FIXED THE CODES WILL SHOW AGAIN..
HOPE THIS HELPS
