Acura RL (1996-2004 year). Manual — part 400
Emission Control System
System Description
The emission control system includes a Three Way Cata-
lytic Converter (TWC), Exhaust Gas Recirculation (EGR)
system, Positive Crankcase Ventilation (PCV) system and
Evaporative Emission (EVAP) system. The emission control
system is designed to meet federal and state emission
standards.
Tailpipe Emission
Inspection
Do not smoke during this procedure. Keep
any open flame away from your work area.
1. Start the engine. Hold the engine at 3,000 rpm with
no load (in Park or neutral) until the radiator fan
comes on, then let it idle.
2. Connect a tachometer.
3. Check and adjust the idle speed, if necessary (see
).
4. Warm up and calibrate the CO meter according to the
meter manufacturer's instructions.
5. Check idle CO with the headlights, heater blower,
rear window defogger, cooling fan, and air condition-
er off.
NOTE: (Canada) Depress the parking brake pedal.
Start the engine, then check that the headlights are
off.
CO meter should indicate 0.1% maximum.
Three Way Catalytic Converter
(TWC)
Description
The Three Way Catalytic Converter (TWC) is used to
convert hydrocarbons (HC), carbon monoxide (CO), and
oxides of nitrogen (NOx) in the exhaust gas, to carbon
dioxide (CO
2
), dinitrogen (N
2
) and water vapor.
SECONDARY HEATED OXYGEN SENSOR (SENSOR 2)
HOUSING
THREE WAY
CATALYSTS
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The scan tool indicates Diagnostic Trouble Code (DTC) P0420: Catalyst system efficiency below threshold.
Description
This system evaluates the catalyst's capacity by means of the HO2S (Primary and Secondary) output during stable driving
conditions. If deterioration has been detected during two consecutive driving cycles, the MIL comes on and DTC P0420 will
be stored.
NOTE: If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then
troubleshoot DTC P0420.
P0136, P0139: Secondary HO2S
P0141: Secondary HO2S Heater
Possible Cause
• TWC Deterioration
• Exhaust system leakage
Troubleshooting Flowchart
— The MIL has been reported on.
— DTC P0420 is stored.
Problem verification:
1. Do the PCM Reset Procedure.
2. Start the engine. Hold the
engine at 3,000 rpm with no
load (in Park or neutral) until
the radiator fan comes on.
3. Connect the ACS service con-
nector.
4. Test-drive 40 - 55 mph (64 -
88 km/h) for approx. 2 min-
utes. Then decelerate for at
least 3 seconds with the throt-
tle completely closed. Then
reduce the vehicle speed to
35 mph (56 km/h), and try to
hold it until the readiness code
comes on.
Is DTC P0420 indicated?
YES
If necessary, replace the TWC.
Intermittent failure, system is OK
at this time.
NO
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Emission Control System
Exhaust Gas Recirculation (EGR) System
Description
The EGR system is designed to reduce oxides of nitrogen emissions (NOx) by recirculating exhaust gas through the EGR
valve and the intake manifold into the combustion chambers. It is composed of the EGR valve, EGR valve vacuum control
valve, EGR valve vacuum control solenoid valve, PCM and various sensors.
The PCM contains memories for ideal EGR valve lifts for varying operating conditions. The EGR valve position sensor
detects the amount of EGR valve lift and sends the information to the PCM. The PCM then compares it with the ideal EGR
valve lift which is determined by signals sent from the other sensors. If there is any difference between the two, the PCM
cuts current to the EGR valve vacuum control solenoid valve to reduce vacuum applied to the EGR valve.
EGR VALVE
POSITION SENSOR
INTAKE MANIFOLD
From No. 20 ECU (PCM)
(20 A) FUSE
(in the under-dash
fuse/relay box)
VARIOUS
SENSORS
EGR VALVE
EGR VALVE
VACUUM
CONTROL
SOLENOID
VALVE
EGR VALVE
VACUUM
CONTROL
VALVE
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The scan tool indicates Diagnostic Trouble Code (DTC) P0420: Insufficient flow in the Exhaust Gas Recirculation
(EGR) system.
Description
Deterioration (clogging, leakage, etc.) in the EGR line or EGR valve is detected by means of the changes in manifold abso-
lute pressure before and after the operation of the EGR valve.
If deterioration has been detected during two consecutive driving cycles, the MIL will come on and DTC P0401 will be
stored.
Possible Causes
• Clogging, leakage in the EGR line
• Faulty EGR valve
Troubleshooting Flowchart
Is DTC P0401 indicated?
Intermittent failure, system is OK
at this time.
YES
Clean the intake manifold EGR
port and EGR passage with car-
buretor cleaner.
Clean the passage inside the
EGR valve with carburetor
cleaner or replace the valve.
NO
Problem verification:
1. Do the PCM Reset Procedure.
2. Connect the ACS service con-
nector.
3. Test-drive under the following
conditions.
— Without any electrical load
— Transmission in posi-
tion
— Decelerate from 55 mph
(88 km/h) for at least 5 sec-
onds.
The MIL has been reported on.
DTC P0401 is stored.
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