System Fault Detection; General Description - Exhaust Gas Recirculation (Egr) System; Egr Purpose; Linear Egr Valve - Isuzu 1999 RODEO Workshop Manual

6E1–440 RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
Fuel Level Sensor – The fuel level sensor is an important
input to the PCM for the enhanced EVAP system
diagnostic. The PCM needs fuel level information to know
the volume of fuel in the tank. The fuel level affects the
rate of change of air pressure in the EVAP system.
Several of the enhanced EVAP system diagnostic
sub–tests are dependent upon correct fuel level
information. The diagnostic will not run when the tank is
less than 15% or more than 85% full. Be sure to diagnose
any Fuel Level Sensor DTCs first, as they can cause
other DTCs to set.
Manifold Absolute Pressure (MAP) Sensor – The
PCM compares the signals from the fuel tank pressure
sensor and the MAP sensor to ensure that a relative
vacuum is maintained in the EVAP system.
Non–Electrical Components
Purge/Vacuum Hoses – Made of rubber compounds,
these hoses route the gasoline fumes from their sources
to the canister and from the canister to the intake air flow.
EVAP Canister – Mounted on a bracket ahead of the fuel
tank, the canister stores fuel vapors until the PCM
determines that engine conditions are right for them to be
removed and burned.
Fuel Tank – The tank has a built–in air space designed for
the collection of gasoline fumes.
Vacuum Source – The vacuum source is split between
two ports, one on either side of the throttle body.
Fuel Cap – The fuel cap is designed to be an integral part
of the EVAP system.

System Fault Detection

The EVAP leak detection strategy is based on applying
vacuum to the EVAP system and monitoring vacuum
decay. The PCM monitors vacuum level via the fuel tank
pressure sensor. At an appropriate time, the EVAP purge
solenoid and the EVAP vent solenoid are turned ON,
allowing the engine vacuum to draw a small vacuum on
the entire evaporative emission system.
After the desired vacuum level has been achieved, the
EVAP purge solenoid is turned OFF, sealing the system.
A leak is detected by monitoring for a decrease in vacuum
level over a given time period, all other variables
remaining constant. A small leak in the system will cause
DTC P0442 to be set.
If the desired vacuum level cannot be achieved in the test
described above, a large leak or a faulty EVAP purge
solenoid is indicated.
Leaks can be caused by the following conditions:
f Disconnected or faulty fuel tank pressure sensor
f Missing or faulty fuel cap
f Disconnected, damaged, pinched, or blocked EVAP
purge line
f Disconnected or damaged EVAP vent hose
f Disconnected, damaged, pinched, or blocked fuel
tank vapor line
f Disconnected or faulty EVAP purge solenoid
f Disconnected or faulty EVAP vent solenoid
f Open ignition feed circuit to the EVAP vent or purge
solenoid
f Damaged EVAP canister
f Leaking fuel sender assembly 0–ring
f Leaking fuel tank or fuel filler neck
A restricted or blocked EVAP vent path is detected by
drawing vacuum into the EVAP system, turning OFF the
EVAP vent solenoid and the EVAP purge solenoid (EVAP
vent solenoid OPEN, EVAP purge Pulse Width Modulate
(PWM) "0%") and monitoring the fuel tank vacuum sensor
input. With the EVAP vent solenoid open, any vacuum in
the system should decrease quickly unless the vent path
is blocked. A blockage like this will set DTC P0446 and
can be caused by the following conditions:
f Faulty EVAP vent solenoid (stuck closed)
f Plugged, kinked or pinched vent hose
f Shorted EVAP vent solenoid driver circuit
f Plugged EVAP canister
The PCM supplies a ground to energize the purge
solenoid (purge ON). The EVAP purge control is PWM, or
turned ON and OFF, several times a second. The duty
cycle (pulse width) is determined by engine operating
conditions including load, throttle position, coolant
temperature and ambient temperature. The duty cycle is
calculated by the PCM and the output is commanded
when the appropriate conditions have been met.
The system checks for conditions that cause the EVAP
system to purge continuously by commanding the EVAP
vent solenoid ON and the EVAP purge solenoid OFF
(EVAP vent solenoid CLOSED, EVAP purge PWM "0%").
If fuel tank vacuum level increases during the test, a
continuous purge flow condition is indicated, which will
set a DTC P1441. This can be caused by the following
conditions:
f EVAP purge solenoid leaking
f EVAP purge and engine vacuum lines switched at the
EVAP purge solenoid
f EVAP purge solenoid driver circuit grounded
GENERAL DESCRIPTION —
EXHAUST GAS RECIRCULATION
(EGR) SYSTEM

EGR Purpose

The exhaust gas recirculation (EGR) system is used to
reduce emission levels of oxides of nitrogen (NOx). NOx
emission levels are caused by a high combustion
temperature. The EGR system lowers the NOx emission
levels by decreasing the combustion temperature.

Linear EGR Valve

The main element of the system is the linear EGR valve.
The EGR valve feeds small amounts of exhaust gas back
into the combustion chamber. The fuel/air mixture will be
diluted and combustion temperatures reduced.

Linear EGR Control

The PCM monitors the EGR actual position and adjusts
the pintle position accordingly. The PCM uses information
from the following sensors to control the pintle position:
f Engine coolant temperature (ECT) sensor.
f Throttle position (TP) sensor.