Toyota Sequoia (2005). Manual - part 113

Status
A/F S1

Status
O2S S2

A/F Condition and A/F and
HO2 Sensors Condition

Misfires

Main Suspected Trouble Areas

Proceed To

Lean

Lean/Rich

Normal

–



 Three–way Catalytic Converter (TWC)



 

Gas leakage from exhaust system

A

A

A

B

B

C

C

Lean/Rich

Lean/Rich

Lean/Rich

Lean/Rich

Lean/Rich

Lean

Lean

Rich

Rich

Rich

Rich

Lean

A/F sensor malfunction

A/F sensor malfunction

HO2 sensor malfunction

HO2 sensor malfunction

Actual air–fuel ratio lean

Actual air–fuel ratio lean

–

–

–

–

May occur



 A/F senso

r



 A/F sensor



 

HO2 sensor



 

HO2 sensor



 

Gas leakage from exhaust system



 

Gas leakage from exhaust system



 

Gas leakage from exhaust system



 

Gas leakage from exhaust system



 Extremely rich or lean actual air–fuel ratio

–



 Extremely rich or lean actual air–fuel ratio

–

DIAGNOSTICS

ENGINE

DI–255

449

Standard:

Tester Display

(Sensor)

Injection Volumes

Status

Voltages

AFS B1S1

(A/F)

+25 %

Rich

Less than 3.0

AFS B1S1

(A/F)

–12.5 %

Lean

More than 3.35

O2S B1S2

(HO2)

+25 %

Rich

More than 0.55

O2S B1S2

(HO2)

–12.5 %

Lean

Less than 0.4

RESULT:

Lean: During A/F CONTROL, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the
HO2 sensor output voltage (O2S) is consistently less than 0.4 V.
Rich: During A/F CONTROL, the AFS is consistently less than 3.0 V, and the O2S is consistently more than
0.55 V.

B

Check and replace A/F sensor.

C

Check and replace heated oxygen sensor and
check and repair exhaust gas leakage.

A

DI–256

–

DIAGNOSTICS

ENGINE

450

3

Check gas leakage on exhaust system.

OK:

No exhaust gas leakage.

NG

Repair or replace exhaust gas leakage point.

OK

Replace front and rear three–way catalytic
converter in the bank a malfunction is de-
tected.

–

DIAGNOSTICS

ENGINE

DI–249

443

DTC

P0420

Catalyst System Efficiency Below Threshold
(Bank 1)

DTC

P0430

Catalyst System Efficiency Below Threshold
(Bank 2)

MONITOR DESCRIPTION

The ECM uses the two sensors, mounted in front of and behind the Three–way Catalytic Converter (TWC),
to monitor its efficiency. 
The first sensor, the Air–Fuel Ratio (A/F) sensor (sensor 1), sends pre–catalyst information to the ECM. The
second sensor, the Heated Oxygen (HO2) sensor (sensor 2), sends post–catalyst information to the ECM.
The ECM compares the information transmitted by these two sensors to determine the efficiency of the TWC
performance and its ability to store oxygen.
When the TWC is functioning properly, the variation in the oxygen concentration in the exhaust gas, after
it has passed through the TWC, is small. In this condition, the voltage output of sensor 2 slowly alternates
between the rich and lean signal voltages (shown in the illustration below). As the TWC performance efficien-
cy deteriorates, its oxygen storage capacity decreases, and the variation in the oxygen concentration in the
exhaust gas increases. As a result, the sensor voltage output fluctuates frequently. 
While the catalyst monitor is running, the ECM measures the signal lengths of both sensors 1 and 2, and
calculates the ratio of the signal lengths to determine the extent of the TWC deterioration. If the deterioration
level exceeds the preset threshold, the ECM interprets this as the TWC malfunction. The ECM then illumi-
nates the MIL and sets the DTC.

DTC No.

DTC Detecting Condition

Trouble Area

P0420

P0430

OSC value smaller than standard value under active air–fuel
ratio control (2 trip detection logic)



Gas leakage on exhaust system



A/F sensor (Bank 1, 2 sensor 1)



Heated oxygen sensor (bank 1, 2 sensor  2)



Three–way catalytic converter

HINT:



Bank 1 refers to the bank that includes cylinder No.1.



Bank 2 refers to the bank that does not include cylinder No.1.



Sensor 1 refers to the sensor mounted in front of the Three–Way Catalytic Converter (TWC) and lo-
cated near the engine assembly.



Sensor 2 refers to the sensor mounted behind the TWC and located far from the engine assembly.

DID87–01

DI–250

–

DIAGNOSTICS

ENGINE

444

MONITOR STRATEGY

R l t d DTC

P0420

Bank 1 catalyst is deteriorated

Related DTCs

P0430

Bank 2 catalyst is deteriorated

Main sensors/components

Front and rear heated oxygen sensor

Required sensors/components

Related sensors/components

Mass air flow meter, Engine coolant temperature

sensor, Engine speed sensor, Intake air tempera-

ture sensor

Frequency of operation

Once per driving cycle

Duration

20 sec.

MIL operation

2 driving cycles

Sequence of operation

None

TYPICAL ENABLING CONDITIONS

It

Specification

Item

Minimum

Maximum

The monitor will run whenever these

DTCs are not present

See page 

DI–18

Battery voltage

11 V

–

Intake air temperature

–10



C (14



F)

–

Engine coolant temperature

75

°

C (167

°

F)

–

Atmospheric pressure coefficient

0.75

–

Idle

OFF

Engine RPM

–

3,200 rpm

A/F sensor

Activated

Fuel system status

Closed loop

Engine load

10 to 70 %

All of the following conditions are met

Condition 1, 2 and 3

1. MAF

6

 

to 75 g/sec

2. Front catalyst temperature (estimated)

620

 

to 830



C (1,148 to 1,526



F)

3. Rear catalyst temperature (estimated)

410 to 830



C (770 to 1,526



F)

Rear HO2S monitor

Completed

Shift position

4th

–

TYPICAL MALFUNCTION THRESHOLDS

Detection Criteria

Threshold

Oxygen storage capacity (OSC) of catalyst

Less than 0.16