2001 DODGE RAM Control vacuum

(1) Disconnect and isolate the battery negative
cable.
(2) Remove the glove box from the instrument
panel. Refer to Glove Box in Instrument Panel Sys-
tem for the procedures.
(3) Reach through the glove box opening to access
and unplug the vacuum harness connector from the
recirculation door actuator (Fig. 27).
(4) Loosen the two nuts that secure the recircula-
tion door actuator to the mounting bracket on the
HVAC housing.
(5) Slide the two actuator mounting studs out of
the slots in the actuator mounting bracket.
(6) Pull the recirculation door actuator downward
far enough to access the clip that retains the actua-
tor link to the recirculation door lever.
(7) Unsnap the clip from the recirculation door
actuator link and disengage the link from the recir-
culation door lever.
(8) Remove the recirculation door actuator from
the HVAC housing.INSTALLATION
NOTE: When reinstalling the recirculation door
actuator, insert a screwdriver or another suitable
tool through the recirculation air intake grille to
prop the recirculation air door up in the open posi-
tion far enough to access the recirculation air door
lever through the instrument panel glove box open-
ing.
NOTE: Before installing the blend door actuator, be
certain that the blend door is not binding.
(1) Snap the clip on the recirculation door actuator
link to engage the link to the recirculation door lever.
(2) Slide the two actuator mounting studs into the
slots in the actuator mounting bracket.
(3) Install the two nuts that secure the recircula-
tion door actuator to the mounting bracket on the
HVAC housing. Tighten the mounting nuts until the
recirculation air door actuator is seated to the
mounting bracket.
(4) Plug in the vacuum harness connector to the
recirculation door actuator.
(5) Install the glove box in the instrument panel.
Refer to Glove Box in Instrument Panel System for
the procedures.
(6) Connect the battery negative cable.
VACUUM CHECK VALVE
DESCRIPTION
On models with a gasoline engine, a vacuum check
valve is installed in the accessory vacuum supply line
near the vacuum tap on the right side of the engine
intake manifold. On models with a diesel engine, a
vacuum check valve is installed on the engine vac-
uum pump. The vacuum check valve is designed to
allow vacuum to flow in only one direction through
the accessory vacuum supply circuits.
OPERATION
The use of a vacuum check valve helps to maintain
the system vacuum needed to retain the selected
HVAC mode and vehicle speed control settings. On
gasoline engine models, it prevents the engine from
bleeding down system vacuum through the intake
manifold during extended heavy engine load (low
engine vacuum) operation. On diesel engine models,
it prevents oil from contaminating the vacuum sup-
ply system by maintaining vacuum in the pump after
the engine is shut-off.
On gasoline engine models, a second vacuum check
valve is installed in the accessory vacuum supply line
at the tee fitting near the dash panel in the engine
Fig. 27 RECIRCULATION DOOR ACTUATOR
1 - DOOR SHAFT RETAINER
2 - RECIRCULATION DOOR
3 - ROD CLIP
4 - BLOWER MOTOR ELECTRICAL CONNECTOR
5 - RECIRCULATION DOOR ACTUATOR
6 - BLOWER MOTOR
7 - VACUUM LINE
24 - 28 CONTROLSBR/BE
RECIRCULATION DOOR ACTUATOR (Continued)

compartment. This check valve also helps to main-
tain the system vacuum needed to retain the selected
HVAC mode settings, but isolates the HVAC vacuum
circuit from the vehicle speed control vacuum circuit.
It prevents the vehicle speed control servo from
bleeding down the HVAC system vacuum during
extended heavy engine load operation.
The vacuum check valve cannot be repaired and, if
faulty or damaged, it must be replaced.
REMOVAL
(1) On models with a gasoline engine, unplug the
vacuum supply line connector at the vacuum check
valve (Fig. 28). On models with a diesel engine,
remove the clamp from the vacuum supply line con-
nector and unplug the connector from the vacuum
check valve (Fig. 29).
(2) On models with a gasoline engine, note the ori-
entation of the check valve in the vacuum supply line
for correct reinstallation.
(3) On models with a gasoline engine, unplug the
remaining line on the vacuum check valve from the
vacuum supply line fitting. On models with a diesel
engine, unscrew the check valve and nipple unit from
the engine vacuum pump.
INSTALLATION
(1) On models with a gasoline engine, plug in the
vacuum check valve to the vacuum line fittings, not-ing the proper orientation of the check valve in the
line. On models with a diesel engine, screw the check
valve and nipple unit into the engine vacuum pump.
Tighten the check valve and nipple unit to 24 N´m
(18 ft. lbs.).
(2) On models with a diesel engine, plug in the
connector to the vacuum check valve and install the
clamp from the vacuum supply line connector.
VACUUM RESERVOIR
DESCRIPTION
Models equipped with a gasoline engine have a
vacuum reservoir. The vacuum reservoir is mounted
in the passenger side cowl plenum area, under the
cowl plenum cover/grille panel. The cowl plenum cov-
er/grille panel must be removed from the vehicle to
access the vacuum reservoir for service.
OPERATION
Engine vacuum is stored in the vacuum reservoir.
The stored vacuum is used to operate the vacuum-
controlled vehicle accessories during periods of low
engine vacuum such as when the vehicle is climbing
a steep grade, or under other high engine load oper-
ating conditions.
The vacuum reservoir cannot be repaired and, if
faulty or damaged, it must be replaced.
Fig. 28 VACUUM CHECK VALVES - GASOLINE
ENGINE
1 - INTAKE MANIFOLD VACUUM TAP
2 - VACUUM CHECK VALVES
Fig. 29 VACUUM CHECK VALVE - DIESEL ENGINE
1 - VACUUM CHECK VALVE
2 - VACUUM SUPPLY LINE
BR/BECONTROLS 24 - 29
VACUUM CHECK VALVE (Continued)

REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the wiper arms from the wiper pivots.
Refer to Wipers/Washers for the procedures.
(3) Remove the weatherstrip along the front edge
of the cowl plenum cover/grille panel and the cowl
plenum panel (Fig. 30).
(4) Remove the plastic screws that secure the cowl
plenum cover/grille panel to the studs on the cowl top
panel near the base of the windshield (Fig. 31).(5) Lift the cowl plenum cover/grille panel from the
cowl top far enough to access the vacuum reservoir
near the right end of the cowl plenum.
(6) Disconnect the vacuum supply hose from the
vacuum reservoir, which is secured to the dash panel
near the right end of the cowl plenum (Fig. 32).
(7) Remove the two nuts that secure the reservoir
to the studs on the dash panel near the right end of
the cowl plenum.
(8) Remove the vacuum reservoir from the dash
panel studs.
INSTALLATION
(1) Install the vacuum reservoir on the dash panel
studs. Tighten the mounting nuts to 2.8 N´m (25 in.
lbs.).
(2) Connect the vacuum supply hose to the vac-
uum reservoir.
(3) Install the plastic screws that secure the cowl
plenum cover/grille panel to the studs on the cowl top
panel.
(4) Install the weatherstrip along the front edge of
the cowl plenum cover/grille panel and the cowl ple-
num panel.
(5) Install the wiper arms on the wiper pivots.
Refer to Wipers/Washers for the procedures.
(6) Connect the battery negative cable.
Fig. 30 COWL PLENUM COVER/GRILLE PANEL
WEATHERSTRIP
1 - COWL GRILLE
2 - WEATHERSTRIP
Fig. 31 COWL PLENUM PLASTIC SCREWS
REMOVAL
1 - PLASTIC SCREW ANCHOR
2 - COWL GRILLE
Fig. 32 VACUUM RESERVOIR REMOVE/INSTALL
1 - COWL PLENUM
2 - VACUUM RESERVOIR
24 - 30 CONTROLSBR/BE
VACUUM RESERVOIR (Continued)

(5) Lift the panel/defrost door out of the top open-
ing of the HVAC housing.
INSTALLATION - HEAT/DEFROST DOOR
(1) Install the heat/defrost door in the HVAC hous-
ing.
(2) Assemble the HVAC housing. (Refer to 24 -
HEATING & AIR CONDITIONING/DISTRIBUTION/
HVAC HOUSING - ASSEMBLY)
(3) Install the heat/defrost door actuator on the
HVAC housing. (Refer to 24 - HEATING & AIR CON-
DITIONING/CONTROLS/MODE DOOR ACTUATOR
- INSTALLATION)
(4) Install the HVAC housing in the vehicle. (Refer
to 24 - HEATING & AIR CONDITIONING/DISTRI-
BUTION/HVAC HOUSING - INSTALLATION)
INSTALLATION - PANEL/DEFROST DOOR
(1) Install the panel/defrost door through the top
opening of the HVAC housing.
(2) Install the defroster and demister duct adapter
on the HVAC housing. (Refer to 24 - HEATING &
AIR CONDITIONING/DISTRIBUTION/DEFROSTER
DUCTS - INSTALLATION)
(3) Install the panel/defrost door actuator on the
HVAC housing. (Refer to 24 - HEATING & AIR CON-
DITIONING/CONTROLS/MODE DOOR ACTUATOR
- REMOVAL)
(4) Install the instrument panel assembly in the
vehicle. Refer to Instrument Panel System for the
procedures.
(5) Connect the battery negative cable.
RECIRCULATION DOOR
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
WARNING: IF THE VEHICLE IS EQUIPPED WITH AIR
CONDITIONING, REVIEW THE WARNINGS AND
CAUTIONS IN PLUMBING BEFORE PERFORMING
THE FOLLOWING OPERATION. (Refer to 24 - HEAT-
ING & AIR CONDITIONING/PLUMBING - WARNING)
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - CAUTION)
(1) Remove the HVAC housing from the vehicle.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL)
(2) Unsnap the recirculation door vacuum actuator
link clip and disengage the link from the recircula-
tion door lever. (Refer to 24 - HEATING & AIR CON-
DITIONING/CONTROLS/RECIRCULATION DOOR
ACTUATOR - REMOVAL)
(3) Using a trim stick or another suitable wide
flat-bladed tool, gently pry the retainer off of the
recirculation door pivot shaft.
(4) Remove the recirculation door through the out-
side air intake opening on the top of the HVAC hous-
ing.
INSTALLATION
(1) Install the recirculation door through the out-
side air intake opening on the top of the HVAC hous-
ing.
(2) Install the retainer on the recirculation door
pivot shaft.
(3) Engage the recirculation door vacuum actuator
link clip with the recirculation door lever. (Refer to
24 - HEATING & AIR CONDITIONING/CONTROLS/
RECIRCULATION DOOR ACTUATOR - INSTALLA-
TION)
(4) Install the HVAC housing in the vehicle. (Refer
to 24 - HEATING & AIR CONDITIONING/DISTRI-
BUTION/HVAC HOUSING - INSTALLATION)
BR/BEDISTRIBUTION 24 - 39
MODE DOOR (Continued)

(M)Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was recorded
(depending if required by CARB and/or EPA). MIL is displayed as an engine icon on instrument panel.
(G)Generator lamp illuminated
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1195 (M) 1/1 O2 Sensor Slow During Catalyst
MonitorA slow switching oxygen sensor has been detected in
bank 1/1 during catalyst monitor test. (Also see SCI DTC
$66) (was P0133)
P1196 (M) 2/1 O2 Sensor Slow During Catalyst
MonitorA slow switching oxygen sensor has been detected in
bank 2/1 during catalyst monitor test. (Also see SCI DTC
$7A) (was P0153)
P1197 1/2 O2 Sensor Slow During Catalyst
MonitorA slow switching oxygen sensor has been detected in
bank 1/2 during catalyst monitor test. (Also see SCI DTC
$68) (was P0139)
P1198 Radiator Temperature Sensor Volts
Too HighRadiator coolant temperature sensor input above the
maximum acceptable voltage.
P1199 Radiator Temperature Sensor Volts
Too LowRadiator coolant temperature sensor input below the
minimum acceptable voltage.
P1281 Engine is Cold Too Long Engine coolant temperature remains below normal
operating temperatures during vehicle travel (Thermostat).
P1282 Fuel Pump Relay Control Circuit An open or shorted condition detected in the fuel pump
relay control circuit.
P1283 Idle Select Signal Invalid ECM or fuel injection pump module internal fault condition
detected.
P1284 (M) Fuel Injection Pump Battery Voltage
Out-Of-RangeFuel injection pump module internal fault condition
detected. Engine power will be derated.
P1285 (M) Fuel Injection Pump Controller
Always OnFuel injection pump module relay circuit failure detected.
Engine power will be derated.
P1286 Accelerator Position Sensor (APPS)
Supply Voltage Too HighHigh voltage detected at APPS.
P1287 Fuel Injection Pump Controller
Supply Voltage LowECM or fuel injection pump module internal fault condition
detected. Engine power will be derated.
P1288 Intake Manifold Short Runner
Solenoid CircuitAn open or shorted condition detected in the short runner
tuning valve circuit.
P1289 Manifold Tune Valve Solenoid Circuit An open or shorted condition detected in the manifold
tuning valve solenoid control circuit.
P1290 CNG Fuel System Pressure Too
HighCompressed natural gas system pressure above normal
operating range.
P1291 No Temp Rise Seen From Intake
HeatersEnergizing Heated Air Intake does not change intake air
temperature sensor an acceptable amount.
P1291 (M) No Temperature Rise Seen From
Intake Air HeatersProblem detected in intake manifold air heating system.
P1292 CNG Pressure Sensor Voltage Too
HighCompressed natural gas pressure sensor reading above
acceptable voltage.
P1293 CNG Pressure Sensor Voltage Too
LowCompressed natural gas pressure sensor reading below
acceptable voltage.
P1294 (M) Target Idle Not Reached Target RPM not achieved during drive idle condition.
Possible vacuum leak or IAC (AIS) lost steps.
25 - 10 EMISSIONS CONTROLBR/BE
EMISSIONS CONTROL (Continued)

(M)Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was recorded
(depending if required by CARB and/or EPA). MIL is displayed as an engine icon on instrument panel.
(G)Generator lamp illuminated
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1295 (M) No 5 Volts to TP Sensor Loss of a 5 volt feed to the Throttle Position Sensor has
been detected.
P1295 (M) Accelerator Position Sensor (APPS)
Supply Voltage Too LowAPPS supply voltage input below the minimum
acceptable voltage.
P1296 No 5 Volts to MAP Sensor Loss of a 5 volt feed to the MAP Sensor has been
detected.
P1297 (M) No Change in MAP From Start To
RunNo difference is recognized between the MAP reading at
engine idle and the stored barometric pressure reading.
P1298 Lean Operation at Wide Open
ThrottleA prolonged lean condition is detected during Wide Open
Throttle
P1299 Vacuum Leak Found (IAC Fully
Seated)MAP Sensor signal does not correlate to Throttle Position
Sensor signal. Possible vacuum leak.
P1388 Auto Shutdown Relay Control Circuit An open or shorted condition detected in the ASD or CNG
shutoff relay control ckt.
P1388 Auto Shutdown Relay Control Circuit An open or shorted condition detected in the auto
shutdown relay circuit.
P1389 No ASD Relay Output Voltage At
PCMNo Z1 or Z2 voltage sensed when the auto shutdown
relay is energized.
P1389 (M) No ASD Relay Output Voltage at
PCMAn open condition detected In the ASD relay output
circuit.
P1390 Timing Belt Skipped 1 Tooth or More Relationship between Cam and Crank signals not correct
P1391 (M) Intermittent Loss of CMP or CKP Loss of the Cam Position Sensor or Crank Position
sensor has occurred. For PL 2.0L
P1398 (M) Mis-Fire Adaptive Numerator at Limit PCM is unable to learn the Crank Sensor's signal in
preparation for Misfire Diagnostics. Probable defective
Crank Sensor
P1399 Wait To Start Lamp Cicuit An open or shorted condition detected in the Wait to Start
Lamp circuit.
P1403 No 5V to EGR Sens Loss of 5v feed to the EGR position sensor.
P01475 Aux 5 Volt Supply Voltage High Sensor supply voltage for ECM sensors is too high.
P1476 Too Little Secondary Air Insufficient flow of secondary air injection detected during
aspirator test (was P0411)
P1477 Too Much Secondary Air Excessive flow of secondary air injection detected during
aspirator test (was P0411).
P1478 Battery Temp Sensor Volts Out of
LimitInternal temperature sensor input voltage out of an
acceptable range.
P1479 Transmission Fan Relay Circuit An open or shorted condition detected in the transmission
fan relay circuit.
P1480 PCV Solenoid Circuit An open or shorted condition detected in the PCV
solenoid circuit.
P1481 EATX RPM Pulse Perf EATX RPM pulse generator signal for misfire detection
does not correlate with expected value.
BR/BEEMISSIONS CONTROL 25 - 11
EMISSIONS CONTROL (Continued)

(M)Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was recorded
(depending if required by CARB and/or EPA). MIL is displayed as an engine icon on instrument panel.
(G)Generator lamp illuminated
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1595 Speed Control Solenoid Circuits An open or shorted condition detected in either of the
speed control vacuum or vent solenoid control circuits.
P1595 Speed Control Solenoid Circuits An open or shorted condition detected in the speed
control vacuum or vent solenoid circuits.
P1596 Speed Control Switch Always High Speed control switch input above maximum acceptable
voltage.
P1597 Speed Control Switch Always Low Speed control switch input below minimum acceptable
voltage.
P1597 Speed Control Switch Always Low Speed control switch input below the minimum acceptable
voltage.
P1598 A/C Pressure Sensor Volts Too High A/C pressure sensor input above maximum acceptable
voltage.
P1598 A/C Sensor Input Hi Problem detected in air conditioning electrical circuit.
P1599 A/C Pressure Sensor Volts Too Low A/C pressure sensor input below minimum acceptable
voltage.
P1599 A/C Sensor Input Lo Problem detected in air conditioning electrical circuit.
P1680 Clutch Released Switch Circuit Problem detected in clutch switch electrical circuit.
P1681 No I/P Cluster CCD/J1850
Messages ReceivedNo CCD/J1850 messages received from the cluster
control module.
P1682 (G) Charging System Voltage Too Low Battery voltage sense input below target charging voltage
during engine operation and no significant change in
voltage detected during active test of generator output
circuit.
P1682 Charging System Voltage Too Low Charging system output voltage low.
P1683 SPD CTRL PWR Relay; or S/C 12v
Driver CKTAn open or shorted condition detected in the speed
control servo power control circuit.
P1683 Spd ctrl pwr rly, or s/c 12v driver
circuitAn open or shorted condition detected in the speed
control servo power control circuit.
P1684 Batt Loss in 50 Star The battery has been disconnected within the last 50
starts
P1685 SKIM Invalid Key The engine controler has received an invalid key from the
SKIM.
P1686 No SKIM BUS Messages Received No CCD/J1850 messages received from the Smart Key
Immobilizer Module (SKIM).
P1687 No MIC BUS Message No CCD/J1850 messages received from the Mechanical
Instrument Cluster (MIC) module.
P1688 (M) Internal Fuel Injection Pump
Controller FailureInternal problem within the fuel injection pump. Low
power, engine derated, or engine stops.
P1689 (M) No Communication Between ECM
and Injection Pump ModuleData link circuit failure between ECM and fuel injection
pump. Low power, engine derated, or engine stops.
P1690 (M) Fuel Injection Pump CKP Sensor
Does Not Agree With ECM CKP
SensorProblem in fuel sync signal. Possible injection pump
timing problem. Low power, engine derated, or engine
stops.
BR/BEEMISSIONS CONTROL 25 - 13
EMISSIONS CONTROL (Continued)

DESCRIPTION - TRIP DEFINITION
The term ªTripº has different meanings depending
on what the circumstances are. If the MIL (Malfunc-
tion Indicator Lamp) is OFF, a Trip is defined as
when the Oxygen Sensor Monitor and the Catalyst
Monitor have been completed in the same drive cycle.
When any Emission DTC is set, the MIL on the
dash is turned ON. When the MIL is ON, it takes 3
good trips to turn the MIL OFF. In this case, it
depends on what type of DTC is set to know what a
ªTripº is.
For the Fuel Monitor or Mis-Fire Monitor (contin-
uous monitor), the vehicle must be operated in the
ªSimilar Condition Windowº for a specified amount of
time to be considered a Good Trip.
If a Non-Contiuous OBDII Monitor fails twice in a
row and turns ON the MIL, re-running that monitor
which previously failed, on the next start-up and
passing the monitor, is considered to be a Good Trip.
These will include the following:
²Oxygen Sensor
²Catalyst Monitor
²Purge Flow Monitor
²Leak Detection Pump Monitor (if equipped)
²EGR Monitor (if equipped)
²Oxygen Sensor Heater Monitor
If any other Emission DTC is set (not an OBDII
Monitor), a Good Trip is considered to be when the
Oxygen Sensor Monitor and Catalyst Monitor have
been completed; or 2 Minutes of engine run time if
the Oxygen Sensor Monitor or Catalyst Monitor have
been stopped from running.
It can take up to 2 Failures in a row to turn on the
MIL. After the MIL is ON, it takes 3 Good Trips to
turn the MIL OFF. After the MIL is OFF, the PCM
will self-erase the DTC after 40 Warm-up cycles. A
Warm-up cycle is counted when the ECT (Engine
Coolant Temperature Sensor) has crossed 160ÉF and
has risen by at least 40ÉF since the engine has been
started.
DESCRIPTION - COMPONENT MONITORS -
GAS ENGINES
There are several components that will affect vehi-
cle emissions if they malfunction. If one of these com-
ponents malfunctions the Malfunction Indicator
Lamp (MIL) will illuminate.
Some of the component monitors are checking for
proper operation of the part. Electrically operated
components now have input (rationality) and output
(functionality) checks. Previously, a component like
the Throttle Position sensor (TPS) was checked by
the PCM for an open or shorted circuit. If one of
these conditions occurred, a DTC was set. Now there
is a check to ensure that the component is working.
This is done by watching for a TPS indication of agreater or lesser throttle opening than MAP and
engine rpm indicate. In the case of the TPS, if engine
vacuum is high and engine rpm is 1600 or greater,
and the TPS indicates a large throttle opening, a
DTC will be set. The same applies to low vacuum if
the TPS indicates a small throttle opening.
All open/short circuit checks, or any component
that has an associated limp-in, will set a fault after 1
trip with the malfunction present. Components with-
out an associated limp-in will take two trips to illu-
minate the MIL.
DESCRIPTION - COMPONENT MONITORS -
DIESEL ENGINES
There are several electrical components that will
affect vehicle emissions if they malfunction. If one of
these components is malfunctioning, a Diagnostic
Trouble Code (DTC) will be set by either the Power-
train Control Module (PCM) or the Engine Control
Module (ECM). The Malfunction Indicator Lamp
(MIL) will then be illuminated when the engine is
running.
These electrically operated components have input
(rationality) and output (functionality) checks. A
check is done by one or more components to check
the operation of another component.
Example:The Intake Manifold Air Temperature
(IAT) sensor is used to monitor intake manifold air
temperature over a period of time after a cold start.
If the temperature has not risen to a certain specifi-
cation during a specified time, a Diagnostic Trouble
Code (DTC) will be set for a problem in the manifold
air heater system.
All open/short circuit checks, or any component
that has an associated limp-in will set a DTC and
trigger the MIL after 1 trip with the malfunction
present. Components without an associated limp-in
will take two trips to illuminate the MIL.
OPERATION - GAS ENGINES
The Powertrain Control Module (PCM) monitors
many different circuits in the fuel injection, ignition,
emission and engine systems. If the PCM senses a
problem with a monitored circuit often enough to
indicate an actual problem, it stores a Diagnostic
Trouble Code (DTC) in the PCM's memory. If the
problem is repaired or ceases to exist, the PCM can-
cels the code after 40 warm-up cycles. Diagnostic
trouble codes that affect vehicle emissions illuminate
the Malfunction Indicator Lamp (MIL). The MIL is
displayed as an engine icon (graphic) on the instru-
ment panel. Refer to Malfunction Indicator Lamp in
this section.
Certain criteria must be met before the PCM
stores a DTC in memory. The criteria may be a spe-
25 - 18 EMISSIONS CONTROLBR/BE
EMISSIONS CONTROL (Continued)