Toyota Tundra. Manual — part 1537

P0136
P0156

decrease to less than
0.21 V

b. HO2 sensor voltage

does not increase to
more than 0.59 V



Low impedance:

Sensor impedance less than 5
ohms for more than 30
seconds when ECM
presumes sensor to be
warmed up and operating
normally (2 trip detection
logic)



HO2 sensor heater (for Bank
1, 2)



Air-fuel Ratio (A/F) sensor
(for Bank 1, 2)



Integration relay



Gas leakage from exhaust
system

P0137
P0157



Low voltage (open):

During active air-fuel ratio
control, following conditions
(a) and (b) met for certain
period of time (2 trip
detection logic):

a. HO2 sensor voltage

output less than 0.21 V

b. Target air-fuel ratio

rich



High impedance:

Sensor impedance 15 kohms
or more for more than 90
seconds when ECM
presumes sensor to be
warmed up and operating
normally (2 trip detection
logic)



Open in HO2 sensor (for
Bank 1, 2) circuit



HO2 sensor (for Bank 1, 2)



HO2 sensor heater (for Bank
1, 2)



Integration relay



Gas leakage from exhaust
system

P0138



High voltage (short):

During active air-fuel ratio
control, following conditions
(a) and (b) met for certain
period of time (2 trip
detection logic):

a. HO2 sensor voltage

output more than 0.59
V



Short in HO2 sensor (for
Bank 1, 2) circuit



HO2 sensor (for Bank 1, 2)



ECM internal circuit

2009 Toyota Tundra

2009 ENGINE PERFORMANCE Engine Control System (3UR-FBE) - Tundra

MONITOR DESCRIPTION

Active Air-Fuel Ratio Control

The ECM usually performs air-fuel ratio feedback control so that the Air-Fuel Ratio (A/F) sensor output
indicates a near stoichiometric air-fuel level. This vehicle includes active air-fuel ratio control in addition to
regular air-fuel ratio control. The ECM performs active air-fuel ratio control to detect any deterioration in the
Three-Way Catalytic Converter (TWC) and Heated Oxygen (HO2) sensor malfunctions (refer to the diagram
below).

Active air-fuel ratio control is performed for approximately 15 to 20 seconds while driving with a warm engine.
During active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become lean or rich by the ECM. If
the ECM detects a malfunction, a DTC is stored.

Abnormal Voltage Output of HO2 Sensor (DTC P0136 and P0156)

While the ECM is performing active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become rich
or lean. If the sensor is not functioning properly, the voltage output variation is small. For example, when the
HO2 sensor voltage does not decrease to less than 0.21 V and does not increase to more than 0.59 V during
active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and stores DTC
P0136 or P0156.

P0158

b. Target air-fuel ratio

lean



Extremely high voltage
(short):

HO2 sensor voltage output
exceeds 1.2 V for more than
10 seconds (2 trip detection
logic)

malfunction



Air-Fuel ratio (A/F) sensor
(for Bank 1, 2)

P0139
P0159

The HO2 sensor voltage does not
drop below 0.2 V immediately after
fuel cut starts.



Short in HO2 sensor (for
Bank 1, 2 Sensor 2) circuit



HO2 sensor (for Bank 1, 2
Sensor 2)



ECM

2009 Toyota Tundra

2009 ENGINE PERFORMANCE Engine Control System (3UR-FBE) - Tundra

Fig. 91: HO2 Sensor Voltage Graph
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

Open or Short in Heated Oxygen (HO2) Sensor Circuit (DTC P0137 and P0157 or P0138 and P0158)

During active air-fuel ratio control, the ECM calculates the Oxygen Storage Capacity (OSC)* of the Three-Way
Catalytic Converter (TWC) by forcibly regulating the air-fuel ratio to become rich or lean. If the HO2 sensor
has an open or short, or the voltage output of the sensor decreases significantly, the OSC indicates an
extraordinarily high value. Even if the ECM attempts to continue regulating the air-fuel ratio to become rich or
lean, the HO2 sensor output does not change.

While performing active air-fuel ratio control, when the target air-fuel ratio is rich and the HO2 sensor voltage
output is below 0.21 V (lean), the ECM interprets this as an abnormally low sensor output voltage and stores
DTC P0137 or P0157. When the target air-fuel ratio is lean and the voltage output is higher than 0.59 V (rich)
during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormally high, and
stores DTC P0138 or P0158.

HINT:

DTC P0138 or P0158 is also stored if the HO2 sensor voltage output is more than 1.2 V for 10 seconds or more.

*: The TWC has the capability to store oxygen. The OSC and the emission purification capacity of the TWC are
mutually related. The ECM determines whether the catalyst has deteriorated based on the calculated OSC value
(see

DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1); DTC P0430

CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 2)

).

Fig. 92: HO2 Sensor Voltage Graph
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

2009 Toyota Tundra

2009 ENGINE PERFORMANCE Engine Control System (3UR-FBE) - Tundra

High or Low Impedance of Heated Oxygen (HO2) Sensor (DTC P0136 and P0156 or P0137 and P157)

Fig. 93: HO2 Sensor Temperature Chart
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

During normal air-fuel ratio feedback control, there are small variations in the exhaust gas oxygen
concentration. In order to continuously monitor the slight variations in the HO2 sensor signal while the engine
is running, the impedance* of the sensor is measured by the ECM. The ECM determines that there is a
malfunction in the sensor when the measured impedance deviates from the standard range.

*: The effective resistance in an alternating current electrical circuit.

HINT:



The impedance cannot be measured using an ohmmeter.



DTC P0136 and P0156 indicate the deterioration of the HO2 sensor. The ECM sets this DTC by
calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving
cycles).



DTC P0137 and P0157 indicate an open or short circuit in the HO2 sensor (2 driving cycles). The ECM
stores this DTC when the impedance of the sensor exceeds the threshold 15 kohms.

HO2 sensor output voltage during fuel cut (P0139 or P0159)

The sensor voltage drops below 0.2 V (extremely lean status) immediately when the vehicle decelerates and
fuel cut is operating. If the voltage does not drop below 0.2 V, the ECM determines that the sensor response
feature has deteriorated, illuminates the MIL and stores DTC(s).

MONITOR STRATEGY

MONITOR STRATEGY

P0136: Heated oxygen sensor (for Bank 1) output voltage (Abnormal
voltage output)
P0136: Heated oxygen sensor (for Bank 1) impedance (Low)
P0137: Heated oxygen sensor (for Bank 1) output voltage (Low
voltage)
P0137: Heated oxygen sensor (for Bank 1) impedance (High)
P0138: Heated oxygen sensor (for Bank 1) output voltage (High

2009 Toyota Tundra

2009 ENGINE PERFORMANCE Engine Control System (3UR-FBE) - Tundra