Toyota Tundra. Manual — part 1181

Fig. 89: Identifying D74 Connector Terminals

OK : REPLACE ECM (See REMOVAL )

19. INSPECT HEATED OXYGEN SENSOR

a. Disconnect the D31 or D32 HO2 sensor connector.

b. Measure the resistance according to the value(s) in the table below.

Standard resistance

TESTER CONNECTION SPECIFIED CONDITION

NG : REPAIR HEATED OXYGEN SENSOR

Tester Connection Condition Specified Condition

2 (+B) - 4 (E2)

Always

10 kohms or higher

2 (+B) - 3 (OX1B)

Always

10 kohms or higher

2 (+B) - 3 (OX2B)

Always

10 kohms or higher

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

Fig. 90: Identifying D31 Or D32 HO2 Sensor Connector Terminals

OK : REPAIR OR REPLACE HARNESS OR CONNECTOR

20. READ DTC OUTPUT (DTC P0139 OR P0159 IS OUTPUT AGAIN)

a. Clear the DTC (See DTC CHECK/CLEAR ).

b. Start the engine.

c. Allow the engine to idle for 15 seconds or more.

d. Read the DTCs.

Result

RESULT CHART

B : CHECK FOR INTERMITTENT PROBLEMS (See CHECK FOR INTERMITTENT
PROBLEMS )

A : REPLACE HEATED OXYGEN SENSOR (See REMOVAL )

DTC P0171 SYSTEM TOO LEAN (BANK 1); DTC P0172 SYSTEM TOO RICH (BANK 1); DTC P0174
SYSTEM TOO LEAN (BANK 2); DTC P0175 SYSTEM TOO RICH (BANK 2)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim
consists of both the short-term and long-term fuel trims.

The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at

Display (DTC Output) Proceed To

P0139 or P0159

A

No output

B

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is rich
or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel
ratio is rich and an increase in the fuel injection volume if it is lean.

Factors such as individual engine differences, wear over time and changes in operating environment cause
short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel
compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-
term fuel trim compensation.

If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as
a malfunction, and the ECM illuminates the MIL and sets a DTC.

DTC TROUBLE DETECTION CONDITION CHART

DTC

No.

DTC Detection Condition

Trouble Area

P0171
P0174

With warm engine and stable air-fuel ratio feedback, fuel
trim considerably in error to lean side (2 trip detection
logic)



Air induction system



Injector blockage



Mass Air Flow (MAF) meter



Engine Coolant Temperature
(ECT) sensor



Fuel pressure



Gas leakage from exhaust
system



Open or short in A/F sensor
(bank 1, 2 sensor 1) circuit



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



A/F sensor heater (bank 1, 2
sensor 1)



Integration relay (A/F relay)



A/F sensor heater circuits



PCV valve and hose



PCV hose connections



ECM

P0172
P0175

With warm engine and stable air-fuel ratio feedback, fuel
trim considerably in error to rich side (2 trip detection
logic)



Injector leakage or blockage



MAF meter



ECT sensor



Ignition system



Fuel pressure



Gas leakage from exhaust
system



Open or short in A/F sensor
(bank 1, 2 sensor 1) circuit

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

HINT:



When DTC P0171 or P0174 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175
is set, the actual air-fuel ratio is on the rich side.



If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 may be set. The MIL is
then illuminated.



When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and
the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.

MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause
changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are
persistent deviations in the short-term fuel trim values. Deviations from the ECM's estimated fuel injection
volumes also affect the average fuel trim learning value, which is a combination of the average short-term fuel
trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air- fuel
ratio). If the average fuel trim learning value exceeds the malfunction thresholds, the ECM interprets this a fault
in the fuel system and sets a DTC.

Example:

The average fuel trim learning value is more than +35% or less than -35%, the ECM interprets this as a fuel
system malfunction.



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



A/F sensor heater (bank 1,2
sensor 1)



Integration relay (A/F relay)



A/F sensor heater circuits



ECM

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra