Dodge ZB 2005 Service Manual page 1126

Throttle Closure. If all of the parameters are met
and it still does not run, with your foot firmly on
the Service Brake, slightly (1/4) open the Throt-
tle and quickly close the Throttle. This will allow
the Purge Free update to happen, and then the
Purge Flow Monitor will Run.
3.2.4 OTHER CONTROLS
CHARGING SYSTEM
The charging system is turned on when the
engine is started and ASD relay energized. When
the ASD relay is on, ASD output voltage is supplied
to the ASD sense circuit at the PCM. This voltage is
connected in some cases, through the PCM and
supplied to one of the generator field terminals
(Gen Source +). All others, the Generator field is
connected directly to the ASD output voltage. The
amount of current produced by the generator is
controlled by the Electronic Voltage Regulator
(EVR) circuitry, in the PCM. Battery temperature is
determined either by IAT, Ambient or Battery tem-
perature sensor. This temperature along with
sensed line voltage is used by the PCM to vary
battery charging. This is accomplished by cycling
the path to ground to the other generator field
terminal (Gen field driver).
LEAK DETECTION PUMP SYSTEM
LEAK DETECTION PUMP OPERATION
The evaporative emission system is designed to
prevent the escape of fuel vapors from the fuel
system. Leaks in the system, even small ones, can
allow fuel vapors to escape into the atmosphere.
Government regulations require onboard testing to
make sure that the evaporative (EVAP) system is
functioning properly. The leak detection system
tests for EVAP system leaks and blockage. It also
performs self-diagnostics.
During self-diagnostics, the Powertrain Control
Module (PCM) first checks the Leak Detection
Pump (LDP) for electrical and mechanical faults. If
the first checks pass, the PCM then uses the LDP to
seal the vent valve and pump air into the system to
pressurize it. If a leak is present, the PCM will
continue pumping the LDP to replace the air that
leaks out. The PCM determines the size of the leak
based on how fast/long it must pump the LDP as it
tries to maintain pressure in the system.
EVAP LEAK DETECTION SYSTEM COMPONENTS
(FIGURE 1)
Service Port: Used with special tools like the
Miller Evaporative Emissions
(EELD) to test for leaks in the system.
EVAP Purge Solenoid: The PCM uses the EVAP
purge solenoid to control purging of excess fuel
vapors stored in the EVAP canister. It remains
closed during leak testing to prevent loss of pres-
sure.
EVAP Canister: The EVAP canister stores fuel
vapors from the fuel tank for purging.
EVAP Purge Orifice: Limits purge volume.
EVAP System Air Filter: Provides air to the LDP
for pressurizing the system. It filters out dirt while
allowing a vent to atmosphere for the EVAP system.
LEAK DETECTION PUMP (LDP) COMPONENTS
The main purpose of the LDP is to pressurize the
fuel system for leak checking. It closes the EVAP
system vent to atmospheric pressure so the system
can be pressurized for leak testing. The diaphragm
is powered by engine vacuum. It pumps air into the
EVAP system to develop a pressure of about 7.5
H O (1/4) psi. A reed switch in the LDP allows the
2
PCM to monitor the position of the LDP diaphragm.
The PCM uses the reed switch input to monitor how
fast the LDP is pumping air into the EVAP system.
This allows detection of leaks and blockage.
The LDP assembly consists of several parts (Fig-
ure 2). The solenoid is controlled by the PCM, and it
connects the upper pump cavity to either engine
vacuum or atmospheric pressure. A vent valve
closes the EVAP system to atmosphere, sealing the
system during leak testing. The pump section of the
LDP consists of a diaphragm that moves up and
down to bring air in through the air filter and inlet
check valve, and pump it out through an outlet
check valve into the EVAP system.
The diaphragm is pulled up by engine vacuum,
and pushed down by spring pressure, as the LDP
solenoid turns on and off. The LDP also has a
magnetic reed switch to signal diaphragm position
Leak Detector
to the PCM. When the diaphragm is down, the
switch is closed, which sends a 12 V (system volt-
age) signal to the PCM. When the diaphragm is up,
5
GENERAL INFORMATION