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DI-586
DIAGNOSTICS - ENGINE (2UZ-FE)
DIDRF-01
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.
DI-587
DIAGNOSTICS - ENGINE (2UZ-FE)
DTC No. DTC Detecting Condition Trouble Area
S Air induction system
S Injector blockage
S Mass air flow meter
S Engine coolant temperature sensor
S Fuel pressure
When air-fuel ratio feedback is stable after warming up the S Gas leakage in exhaust system
P0171
engine, fuel trim is considered to be in error on LEAN side S Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
P0174
(2 trip detection logic) circuit
S Heated oxygen sensor (bank 1, 2 sensor 1)
S Heated oxygen sensor heater (bank 1, 2 sensor 1)
S EFI relay
S PCV piping
S ECM
S Injector leak, blockage
S Mass air flow meter
S Engine coolant temperature sensor
S Ignition system
When air-fuel ratio feedback is stable after warming up the
P0172 S Fuel pressure
engine, fuel trim is considered to be in error on RICH side
P0175 S Gas leakage in exhaust system
(2 trip detection logic)
S Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
S Heated oxygen sensor (bank 1, 2 sensor 1)
S ECM
HINT:
S 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.
S 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.
S 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.
DI-588
DIAGNOSTICS - ENGINE (2UZ-FE)
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 leaning value is more than +35 % or less than -35 %, the ECM interprets this as a fuel
system malfunction.
Fuel
Compensation
P0171, P0174: Amount
+35 (%):
Lean Malfunction Threshold
1.35
1.0
P0172, P0175: 0.65
-35 (%):
Rich Malfunction Threshold
B17394
MONITOR STRATEGY
P0171 Fuel system lean (Bank 1)
P0172 Fuel system rich (Bank 1)
Related DTC
R l t d DTCs
P0174 Fuel system lean (Bank 2)
P0175 Fuel system rich (Bank 2)
Main sensors/components Front oxygen sensor
Required sensors/components Engine coolant temperature sensor, Mass air flow
Related sensors/components
meter, Crankshaft position sensor
Frequency of operation Continuous
Duration Within 10 seconds
MIL operation 2 driving cycles
Sequence of operation None
DI-589
DIAGNOSTICS - ENGINE (2UZ-FE)
TYPICAL ENABLING CONDITIONS
Specification
Item
It
Minimum Maximum
The monitor will run whenever this DTC is
See page DI-437
not present
Battery voltage 11 V -
Fuel system status Closed-loop
Either of the following conditions is met: Condition 1 or 2
1. Engine RPM - 1,000 rpm
2. Intake air amount per revolution 0.26 g/sec. -
Catalyst monitor No executed
TYPICAL MALFUNCTION THRESHOLDS
Detection Criteria Threshold
EVAP purge-cut Executing
Either of the following conditions is met Condition 1 or 2
1. Average between short-term fuel trim and long-term fuel
35% or more (varies with ECT)
trim
2. Average between short-term fuel trim and long-term fuel
-35% or less (varies with ECT)
trim
WIRING DIAGRAM
Refer to DTC P0031 on page DI-507.
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE
TEST. The A/F CONTROL function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated
Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the A/F CONTROL operation using a hand-held tester.
(1) Connect a hand-held tester to the DLC3.
(2) Start the engine and turn the tester ON.
(3) Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
(4) On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE
TEST / A/F CONTROL.
(5) Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT
or LEFT button to change the fuel injection volume).
(6) Monitor the voltage outputs of the A/F and HO2 sensors (AFS B1S1 (AFS B2S1) and OS2 B1S2
(OS2 B2S2)) displayed on the tester.
HINT:
S The A/F CONTROL operation lowers the fuel injection volume by 12.5 % or increases the injection
volume by 25 %.
S Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
DI-590
DIAGNOSTICS - ENGINE (2UZ-FE)
Standard:
Tester Display
Injection Volumes Status Voltages
(Sensor)
AFS B1S1 (AFS B2S1)
+25 % Rich Less than 3.0
(A/F)
AFS B1S1 (AFS B2S1)
-12.5 % Lean More than 3.35
(A/F)
O2S B1S2 (O2S B2S2)
+25 % Rich More than 0.55
(HO2)
O2S B1S2 (O2S B2S2)
-12.5 % Lean Less than 0.4
(HO2)
NOTICE:
The Air-Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2)
sensor has a maximum output delay of approximately 20 seconds.
S Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs
of both the A/F and HO2 sensors.
S To display the graph, select the following menu items on the tester: DIAGNOSIS / ENHANCED OBD
II / ACTIVE TEST / A/F CONTROL / USER DATA / AFS B1S1 and O2S B1S2, and press the YES but-
ton and then the ENTER button followed by the F4 button.
A/F Sensor (Sensor 1) HO2 Sensor (Sensor 2) Main Suspected
Case
Output Voltage Output Voltage Trouble Areas
Injection volume Injection volume
+25 % +25 %
-12.5 % -12.5 %
Output voltage Output voltage
1
More than 3.35 V More than 0.55 V
Less than 3.0 V
OK Less than 0.4V
OK
Injection volume Injection volume
A/F sensor
+25 % +25 %
-12.5 % -12.5 %
A/F sensor heater
2 Output voltage Output voltage A/F sensor circuit
Almost More than 0.55 V
NG OK
no reaction Less than 0.4V
Injection volume Injection volume
+25 % +25 %
HO2 sensor
-12.5 % -12.5 % HO2 sensor heater
3 Output voltage Output voltage HO2 sensor circuit
More than 3.35 V Almost
Less than 3.0V OK no reaction NG
Injection volume Injection volume Injector
+25 % +25 % Fuel pressure
-12.5 % -12.5 %
Gas leakage from
4 Output voltage Output voltage exhaust system
Almost Almost (Air-fuel ratio extremely
NG NG
no reaction no reaction
lean or rich)
DI-591
DIAGNOSTICS - ENGINE (2UZ-FE)
HINT:
S Read freeze frame data using a hand-held tester. Freeze frame data record the engine condition when
malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle
was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and
other data, from the time the malfunction occurred.
S A low A/F sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would
cause the engine to run rich.
S A high A/F sensor voltage could be caused by a lean air-fuel mixture. Check for conditions that would
cause the engine to run lean.
1 Check any other DTCs output (in addition to DTC P0171, P0172, P0174 or P0175).
PREPARATION:
(a) Connect a hand-held tester to the DLC3.
(b) Turn the ignition switch to ON and turn the tester ON.
(c) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.
CHECK:
(a) Read DTCs.
Result:
Display (DTC Output) Proceed To
P0171, P0172, P0174 or P0175 A
P0171, P0172, P0174 or P0175 and other DTCs B
HINT:
If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.
B Go to relevant DTC chart (See page DI-477).
A
2 Check connection of PCV piping.
OK:
PCV hose is connected correctly and is not damaged.
NG Repair or replace PCV piping.
OK
DI-592
DIAGNOSTICS - ENGINE (2UZ-FE)
3 Check air induction system (See page SF-1).
CHECK:
Check the air induction system for vacuum leaks.
NG Repair or replace air induction system.
OK
4 Perform active test (A/F control).
(a) Connect the hand-held tester to the DLC3.
(b) Start the engine and turn the tester ON.
(c) Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
(d) On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST /
A/F CONTROL.
(e) Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT
button to change the fuel injection volume).
(f) Monitor the voltage outputs of A/F and HO2 sensors(AFS B1S1 (AFS B2S1) and O2S B1S2 (O2S
B2S2)) displayed on the tester.
HINT:
S The A/F CONTROL operation lowers the fuel injection volume by 12.5 % or increases the injection
volume by 25 %.
S Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
Standard:
Tester Display
Injection Volumes Status Voltages
(Sensor)
AFS B1S1 (AFS B2S1)
+25 % Rich Less than 3.0
(A/F)
AFS B1S1 (AFS B2S1)
-12.5 % Lean More than 3.35
(A/F)
O2S B1S2 (O2S B2S2)
+25 % Rich More than 0.55
(HO2)
O2S B1S2 (O2S B2S2)
-12.5 % Lean Less than 0.4
(HO2)
Result:
Status Status
A/F Condition and
AFS B1S1 O2S B1S2 Misfires Suspected Trouble Areas Proceed To
A/F Sensor Condition
(AFS B2S1) (O2S B2S2)
Lean/Rich Lean/Rich Normal C
S PCV valve and hose
S PCV hose connections
S Injector blockage
S Gas leakage from exhaust system
Lean Lean Actual air-fuel ratio lean May occur S Air induction system A
S Fuel pressure
S Mass Air Flow (MAF) meter
S Engine Coolant Temperature (ECT)
sensor
DI-593
DIAGNOSTICS - ENGINE (2UZ-FE)
S Injector leakage or blockage
S Gas leakage from exhaust system
S Ignition system
Rich Rich Actual air-fuel ratio rich A
S Fuel pressure
S MAF meter
S ECT sensor
Lean Lean/Rich A/F sensor malfunction S A/F sensor B
Rich Lean/Rich A/F sensor malfunction S A/F sensor B
Lean: During A/F CONTROL, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the
HO2 sensor output voltage (O2S) is consistently less than 0.4 V.
Rich: During A/F CONTROL, the AFS is consistently less than 3.0 V, and the O2S is consistently more than
0.55 V.
B Go to step 11.
C Go to step 15.
A
5 Read value of engine coolant temperature.
PREPARATION:
(a) Connect the hand-held tester to the DLC3.
(b) Turn the ignition switch to ON and turn the tester ON.
(c) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL / COOLANT
TEMP.
CHECK:
(a) Read the COOLANT TEMP twice, when the engine is cold and also when warmed up.
Standard:
With cold engine: Same as ambient air temperature.
With warm engine: Between 75_C and 95_C (167_F and 203_F)
NG Replace engine coolant temperature sensor.
OK
DI-594
DIAGNOSTICS - ENGINE (2UZ-FE)
6 Read value of mass air flow meter.
PREPARATION:
(a) Connect the hand-held tester to the DLC3.
(b) Turn the ignition switch to ON and turn the tester ON.
(c) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL / MAF and
COOLANT TEMP.
(d) Allow the engine to idle until the COOLANT TEMP reaches 75_C (167_F) or more.
CHECK:
(a) Read the MAF with the engine in an idling condition and at an engine speed of 2,500 rpm.
Standard:
MAF while engine idling: Between 1.4 gm/s and 2.3 gm/s (shift position: N, A/C: OFF).
MAF at engine speed of 2,500 rpm: Between 5.4 gm/s and 7.9 gm/s (shift position: N, A/C: OFF).
NG Replace mass air flow meter.
OK
7 Check fuel pressure (See page SF-7).
CHECK:
Check the fuel pressure (high or low pressure).
NG Check and replace fuel pump, pressure regula-
tor, fuel pipe line and filter (See page SF-1).
OK
8 Check exhaust system for gas leakage.
OK:
No exhaust gas leakage.
NG Repair or replace exhaust gas leakage point.
OK
DI-595
DIAGNOSTICS - ENGINE (2UZ-FE)
9 Check for spark and ignition (See page IG-1).
HINT:
If the spark plugs or ignition system malfunction, engine misfire may occur. The misfire counter can be read
with the hand-held tester. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / MIS-
FIRE / CYL#1 (to CYL#8).
NG Repair or replace ignition system.
OK
10 Check injector injection (See page SF-29).
HINT:
If the injectors malfunction, engine misfires may occur. The misfire counter can be read with the hand-held
tester. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / MISFIRE / CYL#1 (to
CYL#8).
NG Replace injector.
OK
11 Check resistance of air-fuel ratio (A/F) sensor heater.
Component Side: PREPARATION:
Disconnect the air-fuel ratio (A/F) sensor connector.
A/F Sensor
CHECK:
Measure resistance between the terminals of the A/F sensor
+B HT connector.
Sensor 1 OK:
AF- AF+ Standard:
Tester Connection Specified Condition
Front View B17396
HT (1) - +B (2) 1.8 to 3.4 at 20_C (68_F)
HT (1) - AF- (4) 10 k or higher
NG Replace air-fuel ratio (A/F) sensor.
OK
DI-596
DIAGNOSTICS - ENGINE (2UZ-FE)
12 Check A/F relay.
PREPARATION:
A/F Relay
Remove the A/F relay from the engine room J/B.
CHECK:
Inspect the A/F relay.
OK:
Standard:
Terminal No. Condition Specified Condition
3-5 Always 10 K or higher
A19288
Apply B+ between
3-5 Below 1
terminals 1 and 2
NG Replace A/F relay.
OK
13 Check for open and short in harness and connector between ECM and A/F sen-
sor.
Wire Harness Side: PREPARATION:
A/F Sensor Connector (a) Disconnect the A10 or A30 A/F sensor connector.
A10
(b) Turn the ignition switch to ON.
A30 CHECK:
HT +B
(a) Measure the voltage between the +B terminal of the A/F
Sensor 1 sensor connector and body ground.
AF+ AF- OK:
Standard:
Front View A23659 Tester Connections Specified Conditions
+B (2) - Body ground 9 to 14 V
PREPARATION:
E6 ECM Connector
(a) Turn the ignition switch to OFF.
(b) Disconnect the E6 ECM connector.
CHECK:
(a) Check the resistance.
HA1A HA2A
OK:
Standard (Check for open):
A2A+ A1A+ Tester Connections Specified Conditions
A2A- A1A- A55007
B17415 HT (A10-1) - HA1A (E6-2)
Below 1
HT (A30-1) - HA2A (E6-1)
AF+ (A10-3) - A1A+ (E6-22)
Below 1
AF+ (A30-3) - A2A+ (E6-23)
AF- (A10-4) - A1A- (E6-30)
Below 1
AF- (A30-4) - A2A- (E6-31)
DI-597
DIAGNOSTICS - ENGINE (2UZ-FE)
Standard (Check for short):
Tester Connections Specified Conditions
HT (A10-1) or HA1A (E6-2) - Body ground
10 k or higher
HT (A30-1) or HA2A (E6-1) - Body ground
AF+ (A10-3) or A1A+ (E6-22) - Body ground
10 k or higher
AF+ (A30-3) or A2A+ (E6-23) - Body ground
AF- (A10-4) or A1A- (E6-30) - Body ground
10 k or higher
AF- (A30-4) or A2A- (E6-31) - Body ground
Reference (Bank 1 Sensor 1 System Drawing):
A/F Relay A/F Sensor ECM
From Heater HA1A
Battery
A/F Heater
Fuse Sensor A1A+
Duty
Control
A1A-
To EFI Relay
A23512
NG Replace or replace harness or connector.
OK
14 Replace air fuel ratio sensor.
NEXT
DI-598
DIAGNOSTICS - ENGINE (2UZ-FE)
15 Perform confirmation driving pattern.
Vehicle Speed
Between
(e)
38 mph and 75 mph
(60 km/h and 120 km/h)
(d)
Idling
Ignition Switch OFF
2 minutes 3 to 5 minutes
Time
(a), (b), (c)
B17397
(a) Connect the hand-held tester to the DLC3.
(b) Turn the ignition switch to ON and turn the tester ON.
(c) Clear DTCs (see page DI-462).
(d) Switch the ECM from normal mode to check mode using the tester (see page DI-463).
(e) Start the engine and warm it up with all the accessories switched OFF.
(f) Drive the vehicle at between 38 mph and 75 mph (60 km/h and 120 km/h) and at an engine speed of
between 1,400 rpm and 3,200 rpm for 3 to 5 minutes.
HINT:
If the system is still malfunctioning, the MIL will be illuminated during step (e).
NOTICE:
If the conditions in this test are not strictly followed, no malfunction will be detected.
NEXT
16 Check whether DTC output recurs (DTC P0171, P0172, P0174 or P0175)
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
P0171, P0172, P0174 or P0175 A
No output B
B Go to step 5.
A
DI-599
DIAGNOSTICS - ENGINE (2UZ-FE)
END
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