Toyota Tundra. Manual — part 1351

1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)

a. Connect the Techstream to the DLC3.

b. Turn the ignition switch to ON.

c. Turn the Techstream ON.

d. Enter the following menus: Powertrain/Engine and ECT/Trouble Codes.

e. Read DTCs.

Result

RESULT REFERENCE

HINT:

If any DTCs other than P0128 are output, troubleshoot those DTCs first.

B : GO TO DTC CHART (See DIAGNOSTIC TROUBLE CODE CHART )

A : Go To Next Step

2. CHECK COOLING SYSTEM

a. Check for defects in the cooling system that might cause the system to be too cold, such as

abnormal radiator fan operation or any modifications.

NG : REPAIR OR REPLACE COOLING SYSTEM

OK : Go To Next Step

3. INSPECT THERMOSTAT

a. Remove the thermostat. (See REMOVAL ).

b. Measure the valve opening temperature of the thermostat.

Standard opening temperature:

80 to 84°C (176 to 183°F)

HINT:

In addition to the above check, confirm that the valve is completely closed when the temperature is
below the standard.

c. Reinstall the thermostat. (See INSTALLATION ).

Result

Proceed To

P0128 is output

A

P0128 and other DTCs are output

B

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra

NG : REPLACE THERMOSTAT . (See THERMOSTAT ).

OK : REPLACE ECM . (See REMOVAL ).

DTC P0136 OXYGEN SENSOR CIRCUIT MALFUNCTION (BANK 1 SENSOR 2); DTC P0137
OXYGEN SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 2); DTC P0138 OXYGEN
SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2); DTC P0139 OXYGEN SENSOR
CIRCUIT SLOW RESPONSE (BANK 1 SENSOR 2); DTC P0156 OXYGEN SENSOR CIRCUIT
MALFUNCTION (BANK 2 SENSOR 2); DTC P0157 OXYGEN SENSOR CIRCUIT LOW VOLTAGE
(BANK 2 SENSOR 2); DTC P0158 OXYGEN SENSOR CIRCUIT HIGH VOLTAGE (BANK 2
SENSOR 2); DTC P0159 OXYGEN SENSOR CIRCUIT SLOW RESPONSE (BANK 2 SENSOR 2)

DESCRIPTION

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide
(NO

x

) components in the exhaust gas, a TWC is used. For the most efficient use of the TWC, the air-fuel ratio

must be precisely controlled so that it is always close to the stoichiometric air-fuel level. For the purpose of
helping the ECM to deliver accurate air-fuel ratio control, a Heated Oxygen (HO2) sensor is used.

The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. Since the
sensor is integrated with the heater that heats the sensing portion, it is possible to detect the oxygen
concentration even when the intake air volume is low (the exhaust gas temperature is low). When the air-fuel
ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The HO2 sensor informs the ECM that
the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V). Conversely, when the air-fuel ratio is
richer than the stoichiometric air-fuel level, the oxygen concentration in the exhaust gas becomes lean. The
HO2 sensor informs the ECM that the post-TWC air-fuel ratio is rich (high voltage, i.e. more than 0.45 V). The
HO2 sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the
stoichiometric level.

The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio after
the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working
improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel
ratio control.

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra

Fig. 81: Sectional View Of Oxygen Sensor

DTC DETECTION CONDITION AND TROUBLE AREA

DTC

Code

DTC Detection Condition

Trouble Area

P0136
P0156



Abnormal voltage output:

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

a. Heated Oxygen (HO2) sensor voltage does not

decrease to less than 0.59 V

b. HO2 sensor voltage does not increase to more than

0.21 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)



Open or short in HO2
sensor (for bank 1, 2)
circuit



HO2 sensor (for bank 1,
2)



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 higher 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
P0158



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 higher than 0.59 V

b. Target air-fuel ratio lean



Extremely high voltage (short):

HO2 sensor voltage output exceeds 1.2 V for more than 10



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



HO2 sensor (for bank 1,
2)



ECM internal circuit
malfunction



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

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra

For Mexico Models

DTC DETECTION CONDITION AND TROUBLE AREA - FOR MEXICO MODELS

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 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 set.

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

seconds (2 trip detection logic)

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)

DTC

Code

DTC Detection Condition

Trouble Area

P0136
P0156

Not applicable

None

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



Open in HO2 sensor
(bank 1, 2 sensor 2)
circuit



HO2 sensor (bank 1,2
sensor 2)



HO2 sensor heater (bank
1, 2 sensor 2)



EFI relay



Gas leak from exhaust
system

P0138
P0158

Not applicable

None

P0139
P0159

Not applicable

None

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra