Inspection Procedure

HINT:

Intelligent 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 an intelligent tester.

Connect an intelligent tester to the DLC3.
Start the engine and turn the tester ON.
Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/ F CONTROL.
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).
Monitor the voltage output of the A/F and HO2 sensors (AFS B1S1 and OS2 B1S2) displayed on the tester.

HINT:

The A/F CONTROL operation lowers the fuel injection volume by 12.5 % or increases the injection volume by 25 %.
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Standard voltage

STANDARD VOLTAGE SPECIFICATIONS

Tester Display (Sensor)	Injection Volumes	Status	Voltages
AFS B1S1 (A/F)	+25 %	Rich	Less than 3.0
AFS B1S1 (A/F)	-12.5 %	Lean	More than 3.35
O2S B1S2 (HO2)	+25 %	Rich	More than 0.55
O2S B1S2 (HO2)	-12.5 %	Lean	Less than 0.4

NOTE: 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.

Fig 1: A/F Sensor And HO2 Sensor Voltage Graph

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
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 B1B2, and press the YES button and then the ENTER button followed by the F4 button.
Read freeze frame data using an intelligent tester or OBD II scan tool. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped/whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
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.
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.

When using intelligent tester:

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)

Connect an intelligent tester to the DLC3.
Turn the ignition switch to ON and turn the tester ON.
Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.

Read DTCs.

Result

DTC RESULT DESCRIPTION

Display (DTC Output)	Proceed to
P0171 or P0172	A
P0171 or P0172 and other DTCs	B

HINT:

If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.

B: GO TO DTC CHART

A: Go to Next Step

CHECK PCV HOSE (CONNECTIONS)
OK:

PCV hose is connected correctly, and is not damaged.

NG: REPAIR OR REPLACE PCV HOSE

OK : Go to Next Step
CHECK AIR INDUCTION SYSTEM
1. Check the air induction system for vacuum leakage.
  OK:
  
  No leakage from air induction system.
NG: REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK : Go to Next Step

PERFORM ACTIVE TEST BY INTELLIGENT TESTER (A/F CONTROL)

Connect the intelligent tester to the DLC3.
Start the engine and turn the tester ON.
Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
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).

Monitor the voltage outputs of the A/F and HOS sensors (AFS B1S1 and O2S B1S2) displayed on the tester.

HINT:

The A/F CONTROL operation lowers the fuel injection volume by 12.5 % or increases the injection volume by 25 %.

Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Standard voltage

STANDARD VOLTAGE SPECIFICATIONS

Tester Display (Sensor)	Injection Volumes	Status	Voltages
AFS B1S1 (A/F)	+25 %	Rich	Less than 3.0
AFS B1S1 (A/F)	-12.5 %	Lean	More than 3.35
O2S B1S2 (HO2)	+25 %	Rich	More than 0.55
O2S B1S2 (HO2)	-12.5 %	Lean	Less than 0.4

Result

DTC RESULT DESCRIPTION

Status AFS B1S1	Status O2S B1S2	A/F Condition and A/F Sensor Condition	Misfires	Suspected Trouble Areas	Proceed to
Lean/Rich	Lean/Rich	Normal	-	-	C
Lean	Lean	Actual air-fuel ratio lean	May occur	PCV valve and hose PCV hose connections Injector blockage Gas leakage from exhaust system Air Induction system Fuel pressure Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor	A
Rich	Rich	Actual air-fuel ratio rich	-	Injector leakage or blockage Gas leakage from exhaust system Ignition system Fuel pressure MAF meter ECT sensor	A
Lean	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B
Rich	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B

Lean: During A/F CONTROL, 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: Go to Next Step

READ VALUE OF INTELLIGENT TESTER (COOLANT TEMP)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch to ON and turn the tester ON.
3. Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL / COOLANT TEMP.
4. 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 : Go to Next Step
READ VALUE OF INTELLIGENT TESTER (MAF)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch to ON and turn the tester ON.
3. Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL / MAF and COOLANT TEMP.
4. Allow the engine to idle until the COOLANT TEMP reaches 75°C (167°F) or more.
5. 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 g/sec. and 2.3 g/sec. (shift position: N, A/C: OFF).
  
  MAF at engine speed of 2,500 rpm:
  
  Between 5.4 g/sec. and 7.9 g/sec. (shift position: N, A/C: OFF).
NG: REPLACE MASS AIR FLOW METER

OK : Go to Next Step
CHECK FUEL PRESSURE
1. Check the fuel pressure (See ON-VEHICLE INSPECTION ).
NG: REPAIR OR REPLACE FUEL SYSTEM

OK : Go to Next Step
CHECK EXHAUST GAS LEAK
OK:

No gas leakage.

NG: REPAIR OR REPLACE EXHAUST SYSTEM

OK : Go to Next Step
CHECK SPARKS AND IGNITION
1. Check for the sparks and the ignition (See ON-VEHICLE INSPECTION ).
  HINT:
  
  If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using an intelligent tester. Select the following menu items: DIAGNOSIS I ENHANCED OBD II / DATA LIST / ALL / CYL #1 (to CYL #4).
NG: REPAIR OR REPLACE IGNITION SYSTEM

OK : Go to Next Step
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
1. Inspect the fuel injector assembly (See INSPECTION ).
  HINT:
  
  If the injectors malfunction, engine misfire may occur. The misfire count can be read using an intelligent tester. Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL / CYL #1 (to CYL #4).
NG: REPLACE FUEL INJECTOR ASSEMBLY

OK : Go to Next Step

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Disconnect the A24 A/F sensor connector.

Fig 2: Identifying A24 A/F Sensor Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Measure the resistance between the terminals of the A/F sensor connector.

Standard resistance

RESISTANCE SPECIFICATIONS

Tester Connections	Specified Conditions
HT (1) - +B (2)	Between 1,8 Ω and 3.4 Ω at 20°C (68°F)
HT (1) - AF- (4)	10 kΩ or higher

Reconnect the A/F sensor connector.

NG: REPLACE AIR FUEL RATIO SENSOR

OK : Go to Next Step

INSPECT EFI RELAY

Fig 3: Inspecting EFI Relay

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Remove the EFI relay from the engine room R/B.

Check the EFI relay resistance.

Standard resistance

RESISTANCE SPECIFICATIONS

Tester Connections	Specified Conditions
3 - 5	10 kΩ or higher
3 - 5	Below 1 Ω (When battery voltage applied to terminals 1 and 2)

Reinstall the EFI relay.

NG: REPLACE EFI RELAY

OK : Go to Next Step

CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)

Disconnect the A24 A/F sensor connector.
Turn the ignition switch to ON.

Measure the voltage between the +B terminal of the A/F sensor connector and body ground.

Standard voltage

STANDARD VOLTAGE SPECIFICATIONS

Tester Connections	Specified Conditions
+B (A24-2) - Body ground	Between 9 V and 14 V

Turn the ignition switch OFF.
Disconnect the E4 ECM connector.

Check the resistance.

Standard resistance (Check for open)

STANDARD RESISTANCE SPECIFICATIONS FOR OPEN

Tester Connections	Specified Conditions
HT (A24-1) - HA1A (E4-5)	Below 1 Ω
AF+ (A24-3) - A1A+ (E4-23)	Below 1 Ω
AF- (A24-4) - A1A- (E4-31)	Below 1 Ω

Standard resistance (Check for short)

STANDARD RESISTANCE SPECIFICATIONS (FOR SHORT)

Tester Connections	Specified Conditions
HT (A24-1) or HA1A (E4-5) - Body ground	10 kΩ or higher
AF+ (A24-3) or A1A+ (E4-23) - Body ground	10 kΩ or higher
AF- (A24-4) or A1A- (E4-31) - Body ground	10 kΩ or higher

Fig 4: Identifying A24 A/F Sensor Connector Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Reconnect the ECM connector.
Reconnect the A/F sensor connector.

Fig 5: Sensor 1 System Diagram

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG: REPAIR OR REPLACE HARNESS OR CONNECTOR

OK : Go to Next Step

REPLACE AIR FUEL RATIO SENSOR
PERFORM CONFIRMATION DRIVING PATTERN

Fig 6: Confirmation Driving Pattern
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
1. Connect the intelligent tester to the DLC3 (Procedure "A").
2. Turn the ignition switch to ON and turn the tester ON (Procedure "B").
3. Clear DTCs (See DTC CHECK / CLEAR ) (Procedure "C").
4. Switch the ECM from normal mode to check mode using the tester (See CHECK MODE PROCEDURE ) (Procedure "D").
5. Start the engine and warm it up with all accessories switched OFF (Procedure "E").
6. 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 (Procedure "F").
  HINT:
  
  If the system is still malfunctioning, the MIL will be illuminated during procedure "E".
  
  NOTE: If the conditions in this test are not strictly followed, no malfunction will be detected.

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

On the intelligent tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.

Read DTCs.

Result

DTC RESULT DESCRIPTION

Display (DTC Output)	Proceed to
No output	A
P0171 or P0172	B

B: Go to step 5

A: END

When Using OBD II Scan Tool:

CHECK AIR INDUCTION SYSTEM
1. Check the air induction system for vacuum leakage.
  OK:
  
  No leakage from air induction system.
NG: REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK : Go to Next Step
CHECK PCV HOSE (CONNECTIONS)
OK:

PCV hose is connected correctly, and is not damaged.

NG: REPAIR OR REPLACE PCV HOSE

OK : Go to Next Step
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
1. Check the injector injection (whether fuel volume is high or low, and whether injection pattern is poor).
NG: REPLACE FUEL INJECTOR ASSEMBLY

OK : Go to Next Step
READ VALUE OF OBD II SCAN TOOL (COOLANT TEMP.)
1. Connect an OBD II scan tool to the DLC3.
2. Turn the ignition switch to ON and turn the scan tool ON.
3. Read the engine coolant temperature value using the scan tool twice, when the engine is cold and also 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 : Go to Next Step
READ VALUE OF OBD II SCAN TOOL (MAF)
1. Connect the OBD II scan tool to the DLC3.
2. Turn the ignition switch to ON and turn the scan tool ON.
3. Allow the engine to idle until the engine coolant temperature reaches 75°C (167°F).
4. Read the mass air flow rate value with the engine in an idling condition and at an engine speed of 2,500 rpm.
  Standard:
  
  Mass air flow rate while engine idling:
  
  Between 1.4 g/sec. and 2.3 g/sec. (shift position: N, A/C: OFF).
  
  Mass air flow rate at engine speed of 2,500 rpm:
  
  Between 5.4 g/sec. and 7.9 g/sec. (shift position: N, A/C: OFF).
NG: REPLACE MASS AIR FLOW METER

OK : Go to Next Step
CHECK FOR SPARKS AND IGNITION
1. Check for the sparks and the ignition (See ON-VEHICLE INSPECTION ).
  OK:
  
  Sparks occur.
NG: REPAIR OR REPLACE IGNITION SYSTEM

OK : Go to Next Step
CHECK FUEL PRESSURE
1. Check the fuel pressure (See ON-VEHICLE INSPECTION ).
NG: REPAIR OR REPLACE FUEL SYSTEM

OK : Go to Next Step
CHECK FOR EXHAUST GAS LEAK
OK:

No gas leakage.

NG: REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT

OK : Go to Next Step

READ VALUE OF OBD II SCAN TOOL (OUTPUT VOLTAGE OF A/F SENSOR)

Connect the OBD II scan tool to the DLC3.
Start the engine and turn the scan tool ON.
Warm up the Air-Fuel Ratio (A/F) sensor at an engine speed of 2,500 rpm for 90 seconds.

Using the scan tool, check the A/F sensor voltage three times, once when the engine is in each of the following conditions:

While idling (check for at least 30 seconds) (Step (1))
At an engine speed of approximately 2,500 rpm (without any sudden changes in engine speed) (Step (2))

Raise the engine speed to 4,000 rpm and then quickly release the accelerator pedal so that the throttle valve is fully closed (Step (3)).

Standard voltage

STANDARD VOLTAGE SPECIFICATIONS

Conditions	A/F Sensor Voltage Variations	Reference
Steps (1) and (2)	Changes at approx. 0.66 V	Between 0.62 V and 0.7 V
Step (3)	Increases to 0.76 V or more	This occurs during engine deceleration (when fuel-cut performed)

For more information, see the diagrams below.

Fig 7: A/F Sensor Voltage Variation Conditions

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

If the output voltage of the A/F sensor remains at approximately 0.66 V (see Malfunction Condition diagram) under any conditions, including those above, the A/F sensor may have an open circuit. (This will also happen if the A/F sensor heater has an open circuit.)
If the output voltage of the A/F sensor remains at either approximately 0.76 V or more, or 0.56 V or less (see Malfunction Condition diagram) under any conditions, including those above, the A/F sensor may have a short circuit.
The ECM stops fuel injection (fuel cut) during engine deceleration. This causes a lean condition and results in a momentary increase in the A/F sensor output voltage.
The ECM must establish a closed throttle valve position learning value to perform fuel cut. If the battery terminal has been reconnected, the vehicle must be driven over 10 mph (16 km/h) to allow the ECM to learn the closed throttle valve position.
When the vehicle is driven:
The output voltage of the A/F sensor may be below 0.56 V during fuel enrichment. For the vehicle, this translates to a sudden increase in speed with the accelerator pedal fully depressed when trying to overtake another vehicle. The A/F sensor is functioning normally.
The A/F sensor is a current output element; therefore, the current is converted into a voltage inside the ECM. Measuring the voltage at the connectors of the A/F sensor or ECM will show a constant voltage result.

NG: Go to step 16

OK : Go to Next Step

PERFORM CONFIRMATION DRIVING PATTERN

Fig 8: Confirmation Driving Pattern
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
1. Connect the OBD II scan tool to the DLC3 (Procedure "A").
2. Turn the ignition switch to ON and turn the scan tool ON (Procedure "B").
3. Clear DTCs (See DTC CHECK / CLEAR ) (Procedure "C").
4. Start the engine and warm it up for 2 minutes with all the accessories switched OFF (Procedure "D").
5. 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 (Procedure "E").
6. Turn the ignition switch to OFF (Procedure "F").
7. Repeat procedures "D" and "E" described above (Procedure "G").
8. Go to the next step (Procedure "H")
  HINT:
  
  The MIL will be illuminated during procedure "E" at the second time if a malfunction still exists.
  NOTE:
  - If conditions in this test are not strictly followed, no malfunction will be detected.

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Read DTCs using the OBD II scan tool.

Result

DTC RESULT DESCRIPTION

Display (DTC Output)	Proceed to
P0171 or P0172	A
No output	B

B: Go to step 15

A: Go to Next Step

REPLACE AIR FUEL RATIO SENSOR
1. Replace the air-fuel ratio sensor.
PERFORM CONFIRMATION DRIVING PATTERN (REFER TO STEP 10)

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Read DTCs using the OBD II scan tool.

Result

DTC RESULT DESCRIPTION

Display (DTC Output)	Proceed to
No output	A
P0171 or P0172	B

NOTE: After replacing the ECM, perform confirmation driving pattern (refer to step 10).

B: REPLACE ECM

A: Go to Next Step

CONFIRM IF VEHICLE HAS RUN OUT OF FUEL IN PAST
NO : CHECK INTERMITTENT PROBLEMS

YES : DTC CAUSED BY RUNNING OUT OF FUEL (DTC P0171 OR P0172)

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Disconnect the A24 A/F sensor connector.

Fig 9: Identifying A24 A/F Sensor Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Measure the resistance between the terminals of the A/F sensor connector.

Standard resistance

RESISTANCE SPECIFICATIONS

Tester Connections	Specified Conditions
HT (1) - +B (2)	Between 1.8 Ω and 3.4 a at 20°C (68°F)
HT (1) - AF - (4)	10 kΩ or higher

Reconnect the A/F sensor connector.

NG: REPLACE AIR FUEL RATIO SENSOR

OK : Go to Next Step

INSPECT EFI RELAY

Fig 10: Inspecting EFI Relay

Remove the EFI relay from the engine room R/B.

Check the EFI relay resistance.

Standard resistance

RESISTANCE SPECIFICATIONS

Tester Connections	Specified Conditions
3 - 5	10 kΩ or higher
3 - 5	Below 1 Ω (When battery voltage applied to terminals 1 and 2)

Reinstall the EFI relay.

NG: REPLACE EFI RELAY

OK : Go to Next Step

CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)

Disconnect the A24 A/F sensor connector.
Turn the ignition switch to ON.

Measure the voltage between the +B terminal of the A/F sensor connector and body ground.

Standard voltage

STANDARD VOLTAGE SPECIFICATIONS

Tester Connections	Specified Conditions
+B (A24-2) - Body ground	Between 9 V and 14 V

Turn the ignition switch OFF.
Disconnect the E4 ECM connector.

Check the resistance.

Standard resistance (Check for open)

STANDARD RESISTANCE SPECIFICATIONS FOR OPEN

Tester Connections	Specified Conditions
HT (A24-1) - HA1A (E4-5)	Below 1 Ω
AF+ (A24-3) - A1A+ (E4-23)	Below 1 Ω
AF- (A24-4) - A1A- (E4-31)	Below 1 Ω

Standard resistance (Check for short)

STANDARD RESISTANCE SPECIFICATIONS (FOR SHORT)

Tester Connections	Specified Conditions
HT (A24-1) or HA1A (E4-5) - Body ground	10 kΩ or higher
AF+ (A24-3) or A1A+ (E4-23) - Body ground	10 kΩ or higher
AF- (A24-4) or A1A- (E4-31) - Body ground	10 kΩ or higher

Fig 11: Identifying A24 A/F Sensor Connector Terminals

Reconnect the ECM connector.

NG: REPAIR OR REPLACE HARNESS OR CONNECTOR

OK : Go to Next Step

REPLACE AIR FUEL RATIO SENSOR
1. Replace the air-fuel ratio sensor.
PERFORM CONFIRMATION DRIVING PATTERN (REFER TO STEP 10)

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Read DTCs using the OBD II scan tool.

Result

DTC RESULT DESCRIPTION

Display (DTC Output)	Proceed to
No output	A
P0171 or P0172	B

NOTE: When replacing the ECM, perform confirmation driving pattern (refer to step 10).

B: REPLACE ECM

A: Go to Next Step

CONFIRM IF VEHICLE HAS RUN OUT OF FUEL IN PAST
NO : CHECK FOR INTERMITTENT PROBLEMS

YES : DTC CAUSED BY RUNNING OUT OF FUEL (DTC P0171 OR P0172)