1993 CHEVROLET PLYMOUTH ACCLAIM temperature

of the 5-way connector. If continuity is not present,
repair circuit for an open. If present, continue to step
4.(4) Install 5-way connector back into the mode
door actuator. Then check for continuity between
pins #7 and #16 of the 21-way connector. If continu-
ity is present, replace the ATC control. If continuity
is not present, replace the mode door actuator.
DIAGNOSTIC TROUBLE CODE 19ÐMODE DOOR FEEDBACK SHORTED TO GROUND
(1) Remove the 21-way connector from the control,
and the 5 way connector from the mode door actua-
tor. (2) Check for continuity between pin #16 of the
21-way connector and chassis ground. If present, re-
pair circuit for short to ground. If not present, con-
tinue to step 3. (3) Plug in the 5-way connector and measure resis-
tance between pins #7 and #16 of the 21-way con-
nector. If the resistance is less than 10 ohms, replace
the actuator. If not, replace the control head.
DIAGNOSTIC TROUBLE CODE 20ÐBLEND DOOR MOVED DURING MODE DOOR TEST
(1) Remove the 21-way connector from the control
and the 5-way connector from the three actuators. (2) Check for continuity between pin #4 of the 21-
way connector and pin #4 of each actuator. If conti-
nuity is not present for a particular actuator circuit,
repair that circuit and retest system. If continuity is
present for all circuits, continue to step 3. (3) Plug in the 5-way connectors and check for re-
sistance between pins #4 and #6 of the 21-way con-
nector for the blend air actuator. Then check pins #4
and #5 of the 21-way connector for the mode actua-
tor. The resistance should be between 20-50 ohms. If
either of the actuators do not pass the resistance
tests, replace that particular actuator and retest the
system. If both pass the resistance test, replace the
ATC control.
DIAGNOSTIC TROUBLE CODE 21ÐROM CHECK SUM ERROR
During the Diagnostics test, the computer will ver-
ify it's own internal program. If it finds any part to
be bad, a Diagnostic Trouble Code 21 will be set.
This Diagnostic Trouble Code is not serviceable. If a
Fail Code 21 occurs, the ATC Control Module must
be replaced.
DIAGNOSTIC TROUBLE CODE 22ÐCOMPUTER ERROR
If incorrect data is found in the ATC Control com-
puter module, a Diagnostic Trouble Code 22 will be
set. This Fail Code is not serviceable. If a Diagnostic
Trouble Code 22 occurs, the ATC Control Module
must be replaced.
DIAGNOSTIC TROUBLE CODE 23ÐBLEND
DOOR FEEDBACK FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met. Diagnostic Trouble Code 23 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control. Follow service procedures for Diagnostic Trouble
Codes 14 and 15 when repairing.
DIAGNOSTIC TROUBLE CODE 24ÐMODE DOOR FEEDBACK FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met. Diagnostic Trouble Code 24 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 From ATC Control. Follow service procedures for Diagnostic Trouble
Codes 18 and 19 when repairing.
DIAGNOSTIC TROUBLE CODE 25ÐAMBIENT TEMPERATURE SENSOR FAILURE
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met. Diagnostic Trouble Code 25 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control. Follow service procedures for Diagnostic Trouble
Code 11 when repairing.
DIAGNOSTIC TROUBLE CODE 26ÐIN-CAR TEMPERATURE SENSOR/ASPIRATOR FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
24 - 82 HEATING AND AIR CONDITIONING Ä

back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met. Diagnostic Trouble Code 26 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control. Follow service procedures for Diagnostic Trouble
Code 12 when repairing.
DIAGNOSTIC TROUBLE CODE 27ÐSUN LOAD SENSOR FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met. Diagnostic Trouble Code 27 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control. Follow service procedures for Diagnostic Trouble
Code 12 when repairing.
DIAGNOSTIC TROUBLE CODE 28ÐWATER TEMPERATURE SENSOR FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met. Diagnostic Trouble Code 28 will be stored within
the ATC Control and must be cleared after the fail- ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control. Follow service procedures for Diagnostic Trouble
Code 10 when repairing.
ERASING DIAGNOSTIC TROUBLE CODES
Diagnostic Trouble Codes 23 through 28 are stored
within the ATC in the computer memory. These
codes may be erased from the memory after the cor-
rect repairs have been made. Intermittent Diagnostic
Trouble Codes 23 through 28 will be stored until
they are erased. (1) Run the DIAGNOSTIC TEST.
(2) Depress the PANEL button to access all Diag-
nostic Trouble Codes. When the Display begins flash-
ing alternating zeros, you can do three things:
² Do nothing, and in five seconds control will return
to normal ATC operation. All codes will remain
stored in the control.
² Depress any button within five seconds, other than
A/C, and stop the test immediately. Control will re-
turn to normal ATC operation.
² Depress the A/C button within five seconds, and
proceed to the erasing procedure. By depressing the
A/C button, you will not erase any Diagnostic Trou-
ble Codes. You will only access the next part of the
procedure. Proceed to step 3. (3) After you depress the A/C button the display
will alternate E's. This is for ERASE. You can now
do two things:
² Do nothing, and in five seconds, all Diagnostic
Trouble Codes from 23 through 28 will be erased
from the ATC control.
² Depress any button within five seconds, and Diag-
nostic Trouble Codes will not be erased. Control will return to normal ATC operation.
Ä HEATING AND AIR CONDITIONING 24 - 83

During the cold start warm-up period and the hot
start time delay, the PCM does not energize the so-
lenoid. 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 ener-
gizes and de-energizes the solenoid approximately 5
to 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 the solenoid energizes. The PCM ad-
justs solenoid pulse width based on engine air flow. A rubber boot covers the duty cycle EVAP purge
solenoid. On 2.5L MPI flexible fuel AA-body vehicles,
the solenoid and bracket attach to the EVAP canister
mounting studs (Fig. 7). On vehicles with 3.0L en-
gines, the solenoid attaches to a bracket mounted to
the right engine mount (Fig. 8). The top of the sole-
noid has the word TOP on it. The solenoid will not
operate unless it is installed correctly.
PRESSURE-VACUUM FILLER CAP
CAUTION: Remove the fuel filler cap to relieve fuel
tank pressure. Remove the cap before disconnect-
ing fuel system components or servicing the fuel
tank.
A pressure-vacuum relief cap seals the fuel tank
(Fig. 9). Tightening the cap on the fuel filler tube
forms a seal between them. The relief valves in the
cap are a safety feature. They prevent possible exces-
sive pressure or vacuum in the tank. Excessive fuel
tank pressure could be caused by a malfunction in
the system or damage to the vent lines. The seal between the cap and filler tube breaks
when the cap is removed. Removing the cap breaks
the seal and relieves fuel tank pressure. If the filler cap needs replacement, only use a sim-
ilar unit.
Fig. 6 Canister Purge SolenoidÐExcept 3.0L and 2.5L MPI
Fig. 7 Duty Cycle EVAP Purge SolenoidÐ2.5L MPIFlexible Fuel AA-Body
Fig. 8 Duty Cycle EVAP Purge SolenoidÐ3.0L Engine
Fig. 9 Pressure Vacuum Filler Cap
25 - 14 EMISSION CONTROL SYSTEMS Ä

EXHAUST EMISSION CONTROLS INDEX
page page
Air Aspiration System ..................... 24
EGR Gas Flow Test ...................... 21
EGR System On-Board Diagnostics ........... 21
EGR Tube ServiceÐ2.2L and 2.5L TBI Engines . 22
EGR Tube ServiceÐ3.0L Engines ............ 22
EGR Tube ServiceÐ3.3L and 3.8L Engines .... 22
EGR Valve ServiceÐ2.2L and 2.5L TBI Engines . 22 EGR Valve ServiceÐ3.0L Engines
........... 22
EGR Valve ServiceÐ3.3L and 3.8L Engines .... 22
Exhaust Gas Recirculation (EGR) System ...... 20
Exhaust Gas Recirculation (EGR) System Test . . 21
Heated Inlet Air System ................... 17
Heated Oxygen Sensor (O
2Sensor) .......... 18
HEATED INLET AIR SYSTEM
2.5L MPI (Flexible Fuel AA-body), Turbo III, 3.0L,
3.3L and 3.8L engines do not use a heated inlet air
system. 2.2L and 2.5L TBI air cleaners have a heated air
assembly (Fig. 1). When ambient temperatures are
low, the assembly warms the air before it enters the
throttle body. The heated air assembly reduces hy-
drocarbon emissions, improves engine warm-up char-
acteristics and minimizes icing.
The heated air assembly contains a vacuum oper-
ated blend door. The blend door opens to either
heated air from a stove on the exhaust manifold or
ambient air (outside air). A vacuum diaphragm oper-
ates the door. A spring opposes the vacuum dia-
phragm. A temperature sensor controls the vacuum
diaphragm (Fig. 2). Adjustment of inlet air tempera-
ture occurs only at road load throttle positions or
when the intake manifold vacuum exceeds the vac-
uum diaphragm spring rate. Air flows through the outside air inlet when ambi-
ent air temperature is 8ÉC (15ÉF) or more above the
air temperature sensor control temperature. When ambient air temperature falls below the con-
trol temperature, air flows through both the ambient
and heated circuits. This occurs after the engine has
been started and the exhaust manifold starts to give
off heat. Colder ambient air cause greater air flow
through the heat stove on the exhaust manifold.
Warmer ambient air results in greater ambient air
flow through the air cleaner snorkel.
HEATED INLET AIR SYSTEM SERVICE
Heated air inlet system malfunctions may affect
driveability and vehicle exhaust emissions. Use the following procedure to determine if the
system functions properly. (1) Inspect the condition of the heat stove to air
cleaner flexible connector and all vacuum hoses. In-
spect them for proper attachment. Replace as neces-
sary. (2) With a cold engine and ambient temperature
less than 46ÉC (115ÉF.), the heat control door (valve
plate) should be in the up (heat on position).
(3) With the engine warmed up and running,
check the temperature of the air entering the snorkel
or passing the sensor. When the temperature of the
Fig. 1 Heated Air Inlet System
Fig. 2 Heated Air Temperature Sensor
Ä EMISSION CONTROL SYSTEMS 25 - 17

air entering the outer end of snorkel is 60ÉC (140ÉF.) or
higher, the door should be in the down (heat off)
position. (4) Remove the air cleaner from the engine and
allow it to cool down to 46ÉC (115ÉF). With 20 inches of
vacuum applied to the sensor, the door should be in the
up (heat on position). If the door does not rise to the
heat on position, check the vacuum diaphragm for
proper operation. (5) To test the diaphragm, apply 20 inches of vacuum
to it with vacuum pump tool number C-4207 or equiva-
lent (Fig. 3). The diaphragm should not bleed down
more than 10 inches of vacuum in 5 minutes. The door
should not lift off the bottom of the snorkel at less than
2 inches of vacuum. The door should be in the full up
position with no more than 4 inches of vacuum. (6) If the vacuum diaphragm does not perform ad-
equately, replace the heated air assembly.
(7) If the vacuum diaphragm performs adequately
but proper temperature is not maintained, replace the
sensor and repeat the temperature checks in steps 2
and 3.
HEATED AIR TEMPERATURE SENSOR SER- VICE
REMOVAL
(1) Remove air cleaner housing from vehicle.
(2) Disconnect vacuum hoses from air temperature
sensor. Remove and discard retainer clips, new clips
are supplied with a new sensor (Fig. 4). (3) Remove and discard sensor and gasket.
INSTALLATION (1) Position gasket on the sensor. Install sensor (Fig.
5). (2) While supporting the sensor on outer diameter,
install new retainer clips securely. Ensure the gasket
compresses to form an air seal. Do not attempt to
adjust the sensor.
HEATED OXYGEN SENSOR (O2SENSOR)
The O2sensor threads into the exhaust manifold. It
provides an input voltage to the powertrain control
module (PCM). The input tells the PCM the oxygen
content of the exhaust gas (Fig. 6, 7, 8, 9, or 10). The
PCM uses this information to fine tune the air-fuel
ratio by adjusting injector pulse width. The O
2sensor produces voltages from 0 to 1 volt,
depending upon the oxygen content of the exhaust gas
in the exhaust manifold. When a large amount of
oxygen is present (caused by a lean air-fuel mixture),
the sensor produces a low voltage. When there is a
lesser amount of oxygen present (rich air-fuel mixture),
the sensor produces a higher voltage. By monitoring
the oxygen content and converting it to electrical
voltage, the sensor acts as a rich-lean switch.
Fig. 3 Testing Vacuum Diaphragm on Heated Air In- let Systems
Fig. 4 Removing Sensor Clips
Fig. 5 Air Temperature Sensor Installation
25 - 18 EMISSION CONTROL SYSTEMS Ä

The oxygen sensor contains a heating element that
keeps it at proper temperature during all operating
modes. Maintaining correct sensor temperature at all times allows the system to enter into closed loop op-
eration sooner and remain in closed loop during pe-
riods of extended idle.
In Closed Loop operation the powertrain control
module (PCM) monitors the O
2sensor input (along
with other inputs) and adjusts the injector pulse
width accordingly. During Open Loop operation the
PCM ignores the O
2sensor input. The PCM adjusts
injector pulse width based on preprogrammed (fixed)
oxygen sensor input values and the current inputs
from other sensors.
REMOVAL
CAUTION: Do not pull on the oxygen sensor wire
when disconnecting the electrical connector.
WARNING: THE EXHAUST MANIFOLD MAY BE EX-
TREMELY HOT. USE CARE WHEN SERVICING THE
OXYGEN SENSOR.
Fig. 6 Heated Oxygen SensorÐ2.5L Engine
Fig. 7 Heated Oxygen SensorÐ2.5L MPI Engine (Flexible Fuel AA-body)
Fig. 8 Heated Oxygen SensorÐTurbo III Engine
Fig. 9 Heated Oxygen SensorÐ3.0L Engine
Fig. 10 Heated Oxygen SensorÐ3.3L/3.8L Engine
Ä EMISSION CONTROL SYSTEMS 25 - 19

(1) Disconnect oxygen sensor electrical connector.
(2) Remove sensor using Tool C-4907 (Fig. 11).
After removing the sensor, the exhaust manifold
threads must be cleaned with an 18 mm X 1.5 + 6E
tap. If reusing the original sensor, coat the sensor
threads with an anti-seize compound such as Loctite
771-64 or equivalent. New sensors have compound on
the threads and do not require additional compound.
Tighten the sensor to 27 N Im (20 ft. lbs.) torque.
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
Certain vehicles equipped with either a 2.2L, 2.5L,
3.0L, 3.3L or 3.8L engines may use a back-pressure
type Exhaust Gas Recirculation (EGR) system (Fig.
12, 13, or 14). 2.5L MPI (Flexible Fuel AA-body) and
Turbo III engines do not use an EGR system. The EGR system reduces oxides of nitrogen (NOx)
in engine exhaust and helps prevent spark knock.
The system allows a predetermined amount of hot
exhaust gas to recirculate and dilute the incoming
air/fuel mixture. The diluted air/fuel mixture reduces
peak flame temperature during combustion. The EGR system consists of:
² EGR tube (connects a passage in the intake mani-
fold to the exhaust manifold)
² EGR valve
² Electronic EGR Transducer (EET)
² Connecting hoses
The electronic EGR transducer (EET) contains an
electrically operated solenoid and a back-pressure
transducer (Fig. 15). The powertrain control module
(PCM) operates the solenoid. The PCM determines
when to energize the solenoid. Exhaust system back-
pressure controls the transducer. When the PCM the solenoid, vacuum does not
reach the transducer. Vacuum flows to the trans-
ducer when the PCM de-energizes the solenoid. When exhaust system back-pressure becomes high
enough, it fully closes a bleed valve in the trans-
ducer. When the PCM de-energizes the solenoid and
back-pressure closes the transducer bleed valve, vac-
uum flows through the transducer to operate the
EGR valve. De-energizing the solenoid, but not fully closing
the transducer bleed hole (because of by low back-
pressure), varies the strength of vacuum applied to
the EGR valve. Varying the strength of the vacuum
changes the amount of EGR supplied to the engine.
This provides the correct amount of exhaust gas re-
circulation for different operating conditions.
Fig. 11 Heated Oxygen Sensor Socket
Fig. 12 EGR SystemÐ2.2L and 2.5L TBI Engines
Fig. 13 EGR SystemÐ3.0L Engines
25 - 20 EMISSION CONTROL SYSTEMS Ä

These systems do not allow EGR at idle. The 2.2L/
2.5L EGR systems operate at all temperatures. The
3.0L, 3.3L and 3.8L EGR systems do not operate
when coolant temperature is below 4.5ÉC (40É)F at
start-up. These systems activate when coolant tem-
perature reaches 77ÉC (170ÉF).
EGR SYSTEM ON-BOARD DIAGNOSTICS
The powertrain control module (PCM) performs an
on-board diagnostic check of the EGR system on all
California vehicles with EGR systems. The diagnos-
tic system uses the Electric EGR Transducer (EET)
for the system tests. The diagnostic check activates only during selected
engine/driving conditions. When the conditions are
met, the PCM energizes the transducer 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 fault if the EGR system has
failed or degraded. After registering a fault, the PCM
turns on the malfunction indicator lamp (instrument
panel Check Engine light). The malfunction indicator
lamp indicates the need for immediate service.
If a problem is indicated by the malfunction indicator
lamp and a diagnostic trouble code for the EGR system,
check for proper operation of the EGR system. Use the
System Test, EGR Gas Flow Test and EGR Diagnosis
Chart. If the EGR system tests properly, check the sys-
tem using the DRBII scan tool. Refer to On-Board Di-
agnosis in the General Diagnosis sections of Group 14.
Also, refer to the DRBII scan tool and the appropriate
Powertrain Diagnostics Procedure manual.
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
TEST
WARNING: APPLY PARKING BRAKE AND/OR
BLOCK WHEELS BEFORE PERFORMING EGR SYS-
TEM TEST.
A failed or malfunctioning EGR system can cause
engine spark knock, sags or hesitation, rough idle,
and/or engine stalling. To ensure proper operation of
the EGR system, all passages and moving parts must
be free of deposits that could cause plugging or stick-
ing. Ensure system hoses do not leak. Replace leak-
ing components. Inspect hose connections between the throttle body,
intake manifold, EGR solenoid and transducer, and
EGR valve. Replace hardened, cracked, or melted
hoses. Repair or replace faulty connectors.
Check the EGR control system and EGR valve with
the engine fully warmed up and running (engine cool-
ant temperature over 150ÉF). With the transmission in
neutral and the throttle closed, allow the engine to idle
for 70 seconds. Abruptly accelerate the engine to ap-
proximately 2000 rpm, but not over 3000 rpm. The EGR
valve stem should move when accelerating the engine
(the relative position of the groove on the EGR valve
stem should change). Repeat the test several times to
confirm movement. If the EGR valve stem moves, the
control system is operating normally. If the control sys-
tem is not operating normally, refer to the EGR Diag-
nosis Chart to determine the cause.
EGR GAS FLOW TEST
The following procedure should be used to determine
if exhaust gas is flowing through the EGR system.
Connect a hand vacuum pump to the EGR valve
vacuum motor. With engine running at idle speed,
slowly apply vacuum. Engine speed should begin to
drop when applied vacuum reaches 2.0 to 3.5 inches.
Fig. 14 EGR MountingÐ3.3L and 3.8L Engines
Fig. 15 Electric EGR Transducer (EET) Assembly
Ä EMISSION CONTROL SYSTEMS 25 - 21