Page 353 of 4323

± DIAGNOSTICSENGINE
DI±159
353 Author: Date:
2005 SEQUOIA (RM1146U)
6 Check whether DTC output recurs (DTC P0138, P0158)
CHECK:
(a) On the hand±held tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / CURRENT CODES.
(b) Read DTCs.
RESULT:
Display (DTC Output)Proceed To
P0138 or P0158A
No outputB
B Check for intermittent problems
(See page DI±11).
A
Replace heated oxygen sensor.
7 Check output voltage of heated oxygen sensor.
PREPARATION:
(a) Connect the hand±held tester to the DLC3.
(b) Turn the ignition switch to ON and turn the tester ON.
(c) Start the engine.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL / O2S B1S2.
(e) After warming up the engine, run the engine at an engine speed of 2,500 rpm for 3 minutes.
CHECK:
(a) Read the output voltage of the HO2 sensor when the engine rpm is suddenly increased.
HINT:
Quickly accelerate the engine to 4,000 rpm 3 times using the accelerator pedal.
Standard: Fluctuates between 0.4 V or less and 0.5 V or more.
NG Go to step 14.
OK
8 Perform confirmation driving pattern.
NEXT
Page 354 of 4323
DI±160
± DIAGNOSTICSENGINE
354 Author: Date:
2005 SEQUOIA (RM1146U)
9 Check whether DTC output recurs (DTC P0136, P0156)
CHECK:
(a) On the hand±held tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / PENDING CODES.
(b) Read DTCs.
RESULT:
Display (DTC Output)Proceed To
P0136 or P0156A
No outputB
B Check for intermittent problems
(See page DI±11).
A
10 Replace heated oxygen sensor.
NEXT
11 Perform confirmation driving pattern.
NEXT
12 Check whether DTC output recurs (DTC P0136, P0156)
CHECK:
(a) On the hand±held tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / PENDING CODES.
(b) Read DTCs.
RESULT:
Display (DTC Output)Proceed To
P0136 or P0156A
No outputB
B Repair completed.
A
Page 355 of 4323

B17391
+12 %
Normal Malfunction±12 %
0 V 3.3 V
1 VA/F Sensor Output
HO2 Sensor OutputInjection Volume
Malfunction
± DIAGNOSTICSENGINE
DI±161
355 Author: Date:
2005 SEQUOIA (RM1146U)
13 Perform active test (injection volume).
PREPARATION:
(a) Connect the hand±held tester to the DLC3.
(b) Start the engine and turn the tester ON.
(c) Warm up the engine.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / INJ VOL.
CHECK:
(a) Change the fuel injection volume using the tester, monitoring the voltage output of Air±Fuel Ratio (A/F)
and HO2 sensors displayed on the tester.
HINT:
Change the fuel injection volume within the range of ±12 % and +12 %. The injection volume can be
changed in 1 % graduations within the range.
The A/F sensor is displayed as AFS B1S1 (AFS B2S1), and the HO2 sensor is displayed as O2S B1S2
(O2S B2S2), on hand±held testers.
RESULT:
Tester Display (Sensor)Voltage VariationsProceed To
AFS B1S1 (AFS B2S1) (A/F)Alternates between more and less than 3.3 VOK
AFS B1S1 (AFS B2S1) (A/F)Remains at more than 3.3 VNG
AFS B1S1 (AFS B2S1) (A/F)Remains at less than 3.3 VNG
HINT:
A normal HO2 sensor voltage (O2S B1S2 (O2S B2S2)) reacts in accordance with increases and decreases
in fuel injection volumes. When the A/F sensor voltage remains at either less or more than 3.3 V despite the
HO2 sensor indicating a normal reaction, the A/F sensor is malfunctioning.
NG Replace air±fuel ratio (A/F) sensor.
OK
Page 356 of 4323
A21341
+B
OX E1HT
H2
H4
Components Side:
Bank 1 Sensor 2, Bank 2 Sensor 2
DI±162
± DIAGNOSTICSENGINE
356 Author: Date:
2005 SEQUOIA (RM1146U)
check and repair extremely rich or lean actu-
arial air fuel ratio (injector, fuel pressure, gas
leakages from exhaust system, etc.)
14 Check for exhaust gas leakage.
CHECK:
Check for exhaust gas leakage from the exhaust manifold and pipe.
OK:
No exhaust gas leakage.
NG Repair or replace exhaust gas leakage point.
OK
15 Inspect heated oxygen sensor.
PREPARATION:
Disconnect the HO2 sensor connector.
CHECK:
Measure the resistance between the terminals of the HO2 sen-
sor connector.
OK:
Standard:
Tester ConnectionsSpecified Conditions
HT (2) ± +B (1)11 to 16 W at 20C (68F)
HT (2) ± E (3)10 kW or higher
NG Replace heated oxygen sensor.
OK
Page 357 of 4323
A19288
EFI Relay
± DIAGNOSTICSENGINE
DI±163
357 Author: Date:
2005 SEQUOIA (RM1146U)
16 Check EFI relay.
PREPARATION:
Remove the EFI relay from the engine room J/B.
CHECK:
Inspect the EFI relay.
OK:
Standard:
Terminal No.ConditionSpecified Condition
3 ± 5Always10 KW or higher
3 ± 5Apply B+ between
terminals 1 and 2Below 1 W
NG Replace EFI relay.
OK
Page 358 of 4323

A23543
+B
OXR2
OXL2E1 HTR2
HTL2
H2
H4
Wire Harness Side:
Bank 1 Sensor 2, Bank 2 Sensor 2
B17416HT1BECM Connector E7OX1B E8
HT2B
OX2B
A21040
Reference (Bank 1 Sensor 1 System Drawing)
From
BatteryEFI No. 1 FuseEFI Relay
EFI No. 2 FuseHeater Oxygen
Sensor
Heater
SensorHT1A
OX1A
E2
MRELECM
DI±164
± DIAGNOSTICSENGINE
358 Author: Date:
2005 SEQUOIA (RM1146U)
17 Check for open and short in harness and connector between ECM and heated
oxygen sensor.
PREPARATION:
(a) Disconnect the heated oxygen sensor connector.
(b) Disconnect the E7 and E8 ECM connector.
CHECK:
Measure the resistance between the wire harness side connec-
tors.
OK:
Standard:
Tester ConnectionSpecified Condition
OXL2 (H2±3) ± OX1B (E8±18)Below 1 W
HTL2 (H2±1) ± HT1B (E8±1)Below 1 W
OXR2 (H4±3) ± OX2B (E7±33)Below 1 W
HTR2 (H4±1) ± HT2B (E7±5)Below 1 W
OXL2 (H2±3) or OX1B (E8±18) ±
Body ground10 kW or higher
HTL2 (H2±1) or HT1B (E8±1) ±
Body ground10 kW or higher
OXR2 (H4±3) or OX2B (E7±33) ±
Body ground10 kW or higher
HTR2 (H4±1) or HT2B (E7±5) ±
Body ground10 kW or higher
NG Repair or replace harness or connector.
OK
Replace heated oxygen sensor.
Page 359 of 4323

± DIAGNOSTICSENGINE
DI±165
359 Author: Date:
2005 SEQUOIA (RM1146U)
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)
CIRCUIT DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim con-
sists 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 stoichio-
metric 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 com-
pensation, 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.
DIDFQ±01
Page 360 of 4323

DI±166
± DIAGNOSTICSENGINE
360 Author: Date:
2005 SEQUOIA (RM1146U)DTC No.
DTC Detecting ConditionTrouble Area
P0171
P0174When air±fuel ratio feedback is stable after warming up the
engine, fuel trim is considered to be in error on LEAN side
(2 trip detection logic)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temperature sensor
Fuel pressure
Gas leakage in exhaust system
Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
Heated oxygen sensor heater (bank 1, 2 sensor 1)
EFI relay
PCV piping
ECM
P0172
P0175When air±fuel ratio feedback is stable after warming up the
engine, fuel trim is considered to be in error on RICH side
(2 trip detection logic)
Injector leak, blockage
Mass air flow meter
Engine coolant temperature sensor
Ignition system
Fuel pressure
Gas leakage in exhaust system
Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
ECM
HINT:
When DTC P0171 or P0174 is recorded, the actual air±fuel ratio is on the LEAN side. When DTC
P0172 or P0175 is recorded, 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 recorded.
The MIL then comes on.
If the total of the short±term fuel trim value and long±term fuel trim value is within 35 % (engine cool-
ant temperature is more than 75 C (167F)), the system is functioning normally.