05-195
DIAGNOSTICS
DTC
P0420
SFI SYSTEM
05FNS-02
CATALYST SYSTEM EFFICIENCY BELOW
THRESHOLD (BANK 1)
MONITOR DESCRIPTION
The ECM uses 2 sensors mounted before and after the three-way catalytic converter (TWC) to monitor its
efficiency. The air-fuel ratio (A/F) sensor (sensor 1) sends pre-catalyst information to the ECM. The heated
oxygen (O2) sensor (sensor 2) sends post-catalyst information to the ECM.
In order to detect deterioration in the catalyst, the ECM calculates Oxygen Storage Capacity (OSC) in the
catalyst based on voltage output of the sensor 2 while performing active air-fuel ratio control instead of
the conventional detecting method which uses the locus ratio.
The OSC is an indication value of the catalyst oxygen storage capacity and is used for representing how
much the catalyst can store oxygen. When the vehicle is being driven with a warm engine, the active air-fuel
ratio control is performed for approximately 15 to 20 seconds. When it is performed, the air-fuel ratio is forcibly regulated to go LEAN or RICH by the ECM, and if a RICH and LEAN cycle of the sensor 2 is long, the
OSC will become greater. The greater OSC and capability of the catalyst are mutually related. The ECM
judges if the catalyst has deteriorated based on the calculated OSC value. The ECM will illuminate the MIL
and a DTC will be set.
DTC No.
P0420
DTC Detection Condition
Trouble Area
OSC value is smaller than the standard value under active
air-fuel ratio control
Exhaust manifold with front catalyst and exhaust front pipe
with rear catalyst
Gas leakage in exhaust system
A/F sensor
Heated oxygen sensor
HINT:
Sensor 1 refers to the sensor mounted before the TWC and is located near the engine assembly.
Sensor 2 refers to the sensor mounted after the TWC and is located far from the engine assembly.
MONITOR STRATEGY
Related DTCs
P0420: Bank 1 catalyst is deterioration
Required sensors/components
Main:
A/F sensor, heated oxygen sensor
Related:
Mass air flow meter, engine coolant temperature sensor, engine speed sensor,
intake air temperature sensor
Frequency of operation
Once per driving cycle
Duration
30 seconds
MIL operation
2 driving cycles
Sequence of operation
None
TYPICAL ENABLING CONDITIONS
The monitor will run whenever the following DTCs are not
present
See page 05-20
Battery voltage
11.5 V or more
Intake air temperature
-10 C (14F) or more
Idle
OFF
Engine speed
Less than 3,200 rpm
Engine coolant temperature
75C (157F) or more
Estimated catalyst temperature conditions are met:
1&2
1. Upstream estimated catalyst temperature
Less than 800C (1,508F), and 430 C (806 F) or more
2. Downstream estimated catalyst temperature
Less than 675C (1,292F), and 290 C (554 F) or more
Fuel system status
Closed-loop
Author:
Date:
360
05-196
DIAGNOSTICS
SFI SYSTEM
TYPICAL MALFUNCTION THRESHOLDS
Oxygen storage capacity
Less than 0.08 g
MONITOR RESULT
The detailed information is described in CHECKING MONITOR STATUS (see page 05-26 ).
MID (Monitor Identification) is assigned to each component/system.
TID (Test Identification) is assigned to each test component.
Scaling is used to calculate the test value indicated on generic OBD scan tools.
Catalyst Bank 1
MID
$21
TID
$A9
Scaling
Multiply by 0.0003 (no dimension)
Description of Test Value
Oxygen storage capacity
CONFIRMATION DRIVING PATTERN FOR READINESS MONITOR
PURPOSE (See page 05-27 )
HINT:
Performing this confirmation pattern will activate the catalyst monitoring by the ECM. This is very useful for
verifying the completion of repairs.
Vehicle Speed
NOTICE:
This test will not be completed
if the vehicle drives under an
absolutely constant speed by
the cruise control etc.
44 to 70 mph
(70 to 113 km/h)
Idling
Power Switch OFF
Warming up
5 to 10 minutes
Time
(Note: Momentary vehicle stop during this drive will not interrupt the test)
Author:
Date:
A79199
361
05-197
DIAGNOSTICS
SFI SYSTEM
(a)
(b)
(c)
READINESS TESTS
MISFIRE MON ..................... AVAIL
FUEL SYS MON ................... AVAIL
COMP MON ........................ AVAIL
CAT EVAL ..................... INCMPL
HTD CAT EVAL ...................... N/A
EVAP EVAL ....................... INCMPL
2nd AIR EVAL .......................... N/A
A/C EVAL ................................ N/A
O2S EVAL .......................... INCMPL
O2S HTR EVAL .................. INCMPL
EGR EVAL ...............................N/A
A76855
A15402
Clear the DTCs.
Connect the hand-held tester to the DLC3.
Select the item: DIAGNOSIS / CARB OBD II / READINESS TESTS. Check that CAT EVAL is INCMPL (incomplete).
(d) Drive the vehicle according to the confirmation driving
pattern. Note the state of the Readiness Tests. They will
change to COMPL (complete) as the CAT evaluation
monitors operate.
(e) Select the item: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / PENDING CODES. Check if any DTC (any pending code) is set.
If the READINESS CODE of CAT EVAL was INCMPL and any
DTC (includes pending codes) was not set, extend the driving
time.
NOTICE:
If you do not have the hand-held tester, perform again the
same confirmation driving pattern after turning OFF the
power switch upon finishing the first confirmation driving
pattern.
CONDITIONING THE A/F SENSOR AND HEATED OXYGEN SENSOR FOR
TESTING
Engine Speed
(c)
2,500 rpm
(d)
1,500 rpm
Idling
Power switch OFF
(b)
(a)
Time
Warmed up
Approximately 3 minutes
2 seconds
(a)
(b)
(c)
(d)
(e)
(f)
Check
A92787
Connect the OBD II scan tool or the hand-held tester to the DLC3.
Put the engine in inspection mode (see page 05-1 ).
Start the engine and warm it up with all the accessories switched OFF until the engine coolant temperature becomes table.
Run the engine at 2,500 rpm for approximately 3 minutes.
Run the engine at 2,500 rpm for 2 seconds and then 1,500 rpm for 2 seconds
Check the waveform of the oxygen sensor (sensor 2).
Author:
Date:
362
05-198
DIAGNOSTICS
SFI SYSTEM
HINT:
If output of the A/F sensor or the heated oxygen sensor does not fluctuate or has noise, the sensor may be
malfunctioning.
If voltage output of both sensors remain at LEAN or RICH, the air-fuel ratio may be extremely LEAN or RICH.
In such a case, perform the following A/F CONTROL operation in ACTIVE TEST using the hand-held tester.
If the catalyst has deteriorated, the voltage output of the heated oxygen sensor fluctuates up and down widely even under normal driving (active air-fuel ratio control is not performed).
Voltage output when active air-fuel ratio control is not performed:
Normal Catalyst
Deteriorated Catalyst
3.5 V
Waveform of
A/F Sensor
before Catalyst
Waveform of Heated
Oxygen Sensor
after Catalyst
3.0 V
1.0 V
0V
10 seconds
10 seconds
A76893
INSPECTION PROCEDURE
HINT:
Read freeze frame data using the handheld tester or the OBD II scan tool. Freeze frame data records the
engine condition when malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean
or rich, and other data from the time the malfunction occurred.
Author:
Date:
363
05-199
DIAGNOSTICS
1
(a)
(b)
(c)
(d)
SFI SYSTEM
CHECK OTHER DTC OUTPUT(IN ADDITION TO DTC P0420)
Connect the hand-held tester or the OBD II scan tool to the DLC3.
Turn the power switch ON (IG).
Turn the hand-held tester or the OBD II scan tool ON.
On the hand-held tester, select the item: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT
CODES.
Read DTCs using the hand-held tester or the OBD II scan tool.
Result:
(e)
Display (DTC Output)
Proceed to
P0420
P0420 and other DTCs
HINT:
If any other codes besides P0420 are output, perform troubleshooting for those DTCs first.
B
GO TO RELEVANT DTC CHART
(See page 05-54 )
CHECK FOR EXHAUST GAS LEAKAGE
OK: No gas leakage.
NG
REPAIR OR REPLACE
LEAKAGE POINT
EXHAUST
GAS
OK
INSPECT AIR FUEL RATIO SENSOR(BANK 1 SENSOR 1) (See page 05-313 )
NG
REPLACE AIR FUEL RATIO SENSOR
OK
INSPECT HEATED OXYGEN SENSOR(BANK 1 SENSOR 2) (See page 05-124 )
NG
REPLACE HEATED OXYGEN SENSOR
OK
REPLACE THREE-WAY CATALYTIC CONVERTER (REPLACE FRONT PIPE)
HINT:
Malfunctioning areas can be found by performing the ACTIVE TEST / A/F CONTROL operation. The A/F
CONTROL operation can determine if the A/F sensor, heated oxygen sensor or other potential trouble area
are malfunctioning or not.
(a) Perform the ACTIVE TEST A/F CONTROL operation.
Author:
Date:
364
05-200
DIAGNOSTICS
SFI SYSTEM
HINT:
The A/F CONTROL operation lowers the injection volume 12.5% or increases the injection volume 25%.
(1) Connect the hand-held tester to the DLC3 on the vehicle.
(2) Turn the power switch ON (IG).
(3) Put the engine in inspection mode (see page 05-1 ).
(4) Warm up the engine by running the engine at 2,500 rpm with the accelerator pedal depressed
more than 60 % for approximately 90 seconds.
(5) Select the item: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
(6) Perform the A/F CONTROL operation with the engine in an idle condition (press the right or left
button).
Result:
A/F sensor reacts in accordance with increase and decrease of injection volume:
+25 % rich output: Less than 3.0 V
-12.5 % lean output: More than 3.35 V
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume:
+25 % rich output: More than 0.55 V
-12.5 % lean output: Less than 0.4 V
NOTICE:
The A/F sensor output has a few seconds of delay and the heated oxygen sensor output has about
20 seconds of delay at maximum.
Author:
Date:
365
05-201
DIAGNOSTICS
Output voltage of A/F sensor
(sensor 1)
+25 %
-12.5 %
-12.5 %
Case 1 Output voltage
OK
More than 0.55 V
Injection volume
+25 %
-12.5 %
-12.5 %
Case 2 Output voltage
A/F sensor
(A/F sensor, sensor heater,
sensor circuit)
Output voltage
NG
Injection volume
More than 0.55 V
OK
Less than 0.4V
Injection volume
+25 %
+25 %
-12.5 %
-12.5 %
Case 3 Output voltage
Heated oxygen sensor
(heated oxygen sensor,
sensor heater, sensor circuit)
Output voltage
More than 3.35 V
OK
Injection volume
Almost
no reaction
NG
Injection volume
+25 %
+25 %
-12.5 %
-12.5 %
Case 4 Output voltage
Almost
no reaction
OK
Less than 0.4V
+25 %
Less than 3.0V
Output voltage
Injection volume
Almost
no reaction
Main Suspect
Trouble Area
Injection volume
+25 %
Less than 3.0 V
SFI SYSTEM
Output voltage of heated oxygen
sensor (sensor 2)
Injection volume
More than 3.35 V
Output voltage
NG
Almost
no reaction
NG
Extremely RICH or LEAN actual air-fuel ratio
(Injector, fuel pressure, gas
leakage in exhaust system,
etc.)
The following A/F CONTROL procedure enables the technician to check and graph the voltage output of
both A/F sensor and the heated oxygen sensor.
To display the graph, enter ACTIVE TEST/ A/F CONTROL/USER DATA, select AFS B1S1 and O2S B1S2
by pressing the YES button followed by the ENTER button and then the F4 button.
Author:
Date:
366
