Toyota Sequoia (2005). Manual — part 90
A19288
EFI Relay
–
DIAGNOSTICS
ENGINE
DI–163
357
16
Check EFI relay.
PREPARATION:
Remove the EFI relay from the engine room J/B.
CHECK:
Inspect the EFI relay.
OK:
Standard:
Terminal No.
Condition
Specified Condition
3 – 5
Always
10 K
Ω
or higher
3 – 5
Apply B+ between
terminals 1 and 2
Below 1
Ω
NG
Replace EFI relay.
OK
A23543
+B
OXR2
OXL2
E1
HTR2
HTL2
H2
H4
Wire Harness Side:
Bank 1 Sensor 2, Bank 2 Sensor 2
B17416
HT1B
ECM Connector
E7
OX1B
E8
HT2B
OX2B
A21040
Reference (Bank 1 Sensor 1 System Drawing)
From
Battery
EFI No. 1 Fuse
EFI Relay
EFI No. 2 Fuse
Heater Oxygen
Sensor
Heater
Sensor
HT1A
OX1A
E2
MREL
ECM
DI–164
–
DIAGNOSTICS
ENGINE
358
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 Connection
Specified Condition
OXL2 (H2–3) – OX1B (E8–18)
Below 1
Ω
HTL2 (H2–1) – HT1B (E8–1)
Below 1
Ω
OXR2 (H4–3) – OX2B (E7–33)
Below 1
Ω
HTR2 (H4–1) – HT2B (E7–5)
Below 1
Ω
OXL2 (H2–3) or OX1B (E8–18) –
Body ground
10 k
Ω
or higher
HTL2 (H2–1) or HT1B (E8–1) –
Body ground
10 k
Ω
or higher
OXR2 (H4–3) or OX2B (E7–33) –
Body ground
10 k
Ω
or higher
HTR2 (H4–1) or HT2B (E7–5) –
Body ground
10 k
Ω
or higher
NG
Repair or replace harness or connector.
OK
Replace heated oxygen sensor.
–
DIAGNOSTICS
ENGINE
DI–165
359
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
DI–166
–
DIAGNOSTICS
ENGINE
360
DTC No.
DTC Detecting Condition
Trouble Area
P0171
P0174
When 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
P0175
When 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 (167
F)), the system is functioning normally.
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