Chrysler DODGE D150 1993 Service Manual page 1488

• EMISSION CONTROL SYSTEMS 25 - 11
• The electrical solenoid portion of the EET is not
energized.
• The engine back pressure entering the EGR valve
inlet is strong enough to close t h e transducer bleed
valve.
If back pressure is not strong enough to close the
transducer bleed valve, the transducer will bleed off
the vacuum preventing EGR operation.
When the electrical solenoid portion of the EET is
de-energized by the powertrain control module
(PCM), vacuum flows to the transducer. The trans­
ducer is connected to the engine exhaust system by a
small hose t h a t connects to t h e base of t h e EGR
valve.
The vacuum section of the transducer is controlled
by exhaust system back pressure. When back pres­
sure is high enough it will close a bleed valve in the
transducer allowing vacuum to actuate the EGR
valve. If back pressure does not close the bleed valve,
vacuum will be bled off.
For more information, refer to Group 14, Fuel Sys­
tems.
Refer to the Component Removal/Installation sec­
tion of this group for EGR valve replacement proce­
dures.
EGR SYSTEM ON-BOARD DIAGNOSTICS
(CALIFORNIA VEHICLES ONLY)
The powertrain control module (PCM) performs an
On-Board Diagnostic (OBD) check of the EGR system
on all California vehicles. The diagnostic system uses
the electric EGR transducer (EET) for the system
tests.
The OBD check activates only during selected en­
gine/driving conditions. When the conditions are met,
the PCM energizes the EET solenoid to disable the
EGR. The PCM checks for a change in the oxygen
sensor signal. If the air-fuel mixture goes lean, the
PCM will attempt to enrichen the mixture. The PCM
registers a diagnostic trouble code (DTC) if the EGR
system has failed or degraded. After registering a
DTC, the PCM turns the m a l f u n c t i o n i n d i c a t o r
l a m p (MIL) on. (The malfunction indicator lamp was
formerly referred to as the check engine lamp). The
malfunction indicator lamp indicates the need for im­
mediate service.
If a malfunction is indicated by the malfunction in­
dicator lamp and a DTC for the EGR system was set,
check for proper operation of EGR system. Use the
following: System Test, EGR Gas Flow Test and EGR
Diagnosis Chart.
If the EGR system tests properly, check the system
using the DRB II scan tool. For use of the DRB II,
refer to the appropriate Powertrain Diagnostics Pro­
cedure service manual.
EGR SYSTEM SERVICE
A malfunctioning EGR system can cause engine
spark knock, sags or hesitation, rough idle, engine
stalling and poor driveability. To be sure of proper
operation of the EGR system, inspect all passages for
blockage. Check moving parts for binding. Inspect
the complete system for leaks. Replace system com­
ponents or hoses t h a t are leaking.
Inspect all hose connections between throttle body,
intake manifold, EGR valve and EGR purge solenoid.
Replace any vacuum harness components that are
leaking or damaged.
Refer to EGR Control System Test and EGR Gas
Flow Test to check EGR System operation.
EGR GAS FLOW TEST
(1) Disconnect hose from EGR valve and connect a
hand vacuum pump to EGR valve nipple. Apply a
minimum of 12 inches vacuum the valve.
(2) The engine should now idle roughly or stall. If
this occurs, the valve is performing correctly. Proceed
to Electric EGR Transducer Test.
(3) If the engine idle speed did not change, remove
the EGR valve and inspect the valve and the exhaust
passage in the manifold for blockage. Repair as nec­
essary. If blockage is not present, replace the EGR
valve.
ELECTRIC EGR TRANSDUCER (EET)
TESTING ELECTRIC SOLENOID PORTION OF TRANSDUCER
(1) Bring the engine to normal operating tempera­
ture. Operate at idle speed. Test the EET as follows:
(2) Check vacuum at EET vacuum source. Discon­
nect the hose and attach a vacuum gauge to it.
(3) Vacuum should be a minimum of 15 inches:
• If vacuum is low, check the line for kinks, twists
or a loose connection at vacuum connector or intake
manifold.
• If vacuum is correct, remove gauge. Connect the
vacuum line and proceed to next step.
(4) Check EET operation using the appropriate
Powertrain Diagnostic Procedures service manual.
Refer to this manual for use of the DRB II scan tool
and repair EET as necessary.
TESTING VACUUM PORTION OF TRANSDUCER
(1) Disconnect the EET vacuum lines, back pres­
sure line and electrical connector. Remove trans­
ducer.
(2) Plug the EET EGR valve port.
(3) Apply 1-2 pounds air pressure to exhaust back
pressure port. Air pressure can be supplied with a
hand operated air pump or compressed air (regulated
to correct psi).
(4) Apply a minimum of 12 inches of vacuum to
vacuum supply port.
Replace the EET if it will not hold vacuum.