Inspection steps

NOTE:

Read the freeze frame data using the SSM3. A part of the engine running conditions under which the engine trouble occurred is recorded in the freeze frame data, which is useful for troubleshooting.
[B1S1] indicates [Bank 1 Sensor 1]. Sensor 1 is the sensor that is installed on the upstream (closest to the engine) of the catalyst.
[B1S2] indicates [Bank 1 Sensor 2]. Sensor 2 is the sensor that is installed on the downstream (far side of the engine) of the catalyst.
When malfunction cannot be located after troubleshooting DTC P0420, abnormally lean or rich condition may be the cause of malfunction. Perform inspection following the inspection procedures for P0171 (lean abnormal) and P0172 (rich abnormal).

Read DTC

Follow the SSM3 on-screen instructions to check the DTC. (Refer to CHECKING/CLEARING DTC )

Result

Result	Go to
Only P0420 is output.	A
Diagnostic codes other than P0420 are also output.	B

NOTE: If any DTCs other than P0420 are output, troubleshoot them first.

B: To corresponding DTC chart (refer to DTC TABLE )

A: Go to next step

Perform SSM3 [System Operation Check Mode] ([Injection Volume])

Connect the SSM3 to the DLC3.
Turn the ignition switch to ON.
Turn on the SSM3.
Start the engine, turn off all the accessory switches, and wait until the engine warms up and the coolant temperature stabilizes. (at 80°C {176°F} or more).
Run the engine at 2500 r/min for approximately three minutes to warm up each sensor.
Select the following menu items using the SSM3. [Inspection of BRZ]/[Each System Check]/[Engine Control System]/[Work Support]/[System Operation Check Mode]/[Injection Volume]

Increase and decrease fuel injection volume, and read values of [A/F Sensor #11] and [O2 Sensor #12].

CAUTION:

The output voltage for the air/fuel ratio sensor is delayed a few seconds, while the output voltage for the oxygen sensor is delayed for a maximum of approximately 20 seconds.
Because the sensors become cold, measure the voltage promptly after warming up the sensors.

NOTE:

Change fuel injection volume from -12 % to +12 %.
If the air/fuel ratio sensor output shows little response, the air/fuel ratio sensor may be at fault.

Voltage

RESISTANCE REFERENCE (SHORT CIRCUIT CHECK)

Item	Fuel injection volume	Output voltage of air/fuel ratio sensor and oxygen sensor
[A/F Sensor #11]	+12 % increase	Less than 2.0 V (rich state)
[A/F Sensor #11]	-12 % decrease	2.4 V or more (lean state)
[Oxygen sensor #12]	+12 % increase	0.55 V or more (rich state)
[Oxygen sensor #12]	-12 % decrease	Less than 0.4 V (lean state)

Result

[AFS Voltage B1S1] result	[O2S B1S2] result	State of air/fuel ratio, air/fuel ratio sensor, and oxygen sensor	Misfiring	Inspection parts	Go to
Rich/Lean	Rich/Lean	Normal	-	Exhaust manifold (front catalyst) Exhaust pipe assembly FR (rear catalyst) Exhaust gas leakage	A
Lean	Rich/Lean	Malfunction in the air/fuel ratio sensor	-	Air/fuel ratio sensor	B
Rich	Rich/Lean	Malfunction in the air/fuel ratio sensor	-	Air/fuel ratio sensor	B
Rich/Lean	Lean	Oxygen sensor failure	-	Oxygen sensor Exhaust gas leakage	C
Rich/Lean	Rich	Oxygen sensor failure	-	Oxygen sensor Exhaust gas leakage	C
Lean	Lean	Lean state	Possible	Extremely lean state Exhaust gas leakage	D
Rich	Rich	Rich state	-	Extremely rich state Exhaust gas leakage	D

NOTE:

Lean status: When [System Operation Check Mode] is performed, the output voltage of the air/fuel ratio is 2.4 V or more, and the output voltage of oxygen sensor remains at less than 0.4 V.
Rich status: When [System Operation Check Mode] is performed, the output voltage of the air/fuel ratio sensor remains at less than 2.0 V, and the output voltage of the oxygen sensor remains at 0.55 V or more.
Rich/lean status: When the [System Operation Check Mode] is performed, the output voltage of the air/fuel ratio sensor and oxygen sensor are normal.
For details of [A/F Sensor #11] and [O2 Sensor #12] under the ECM [Current Data Display & Save] menu, check [Current Data Display & Save]/[System Operation Check Mode]. (Refer to CURRENT DATA DISPLAY & SAVE/SYSTEM OPERATION CHECK MODE )

B: Replacement of the air/fuel ratio sensor (refer to AIR/FUEL RATIO SENSOR (FA20) )

C: Go to Step 5.

D: Go to Step 6.

A: Go to next step

Exhaust gas leakage check
1. Make sure that exhaust gas is not leaking from connections of exhaust pipes and installation areas of sensors.
  Criteria: There is no exhaust leakage.
  
  NG: Repair of exhaust gas leakage
  
  OK: Go to next step
Replacement of exhaust manifold (front catalyst)
1. Replace the exhaust manifold (front catalyst). (refer to REMOVAL )
  Next: Replacement of exhaust pipe assembly FR (rear catalyst) (refer to REMOVAL )
Exhaust gas leakage check
1. Make sure that exhaust gas is not leaking from connections of exhaust pipes and installation areas of sensors.
  Criteria: There is no exhaust leakage.
  
  NG: Repair of exhaust gas leakage
  
  OK: Replacement of oxygen sensor (refer to REMOVAL )
Exhaust gas leakage check
1. Make sure that exhaust gas is not leaking from connections of exhaust pipes and installation areas of sensors.
  Criteria: There is no exhaust leakage.
  
  NG: Repair of exhaust gas leakage
  
  OK: Remove the cause of extremely abnormal lean or rich state (Refer to DTC P0171 SYSTEM TOO LEAN (BANK 1); DTC P0172 SYSTEM TOO RICH (BANK 1); DTC P1170 FUEL SYSTEM ABNORMAL (PORT); DTC P117B FUEL SYSTEM ABNORMAL (DI) )