Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda MX-5 Miata. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0420 [BP, BP WITH TC] DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA HAS BEEN RECORDED Has FREEZE FRAME DATA been recorded?	Yes	Go to the next step.
1		No	Record FREEZE FRAME DATA on repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Check for related Service Bulletins and/or online repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		No	Go to the next step.
3	VERIFY RELATED PENDING CODE OR STORED DTCS Turn ignition key to OFF then ON (Engine off). Verify related pending code or stored DTCs. Are there other DTCs?	Yes	Go to appropriate DTC troubleshooting.
3		No	Go to the next step.
4	INSPECT GAS LEAKAGE OF EXHAUST SYSTEM Visually inspect exhaust gas leakage in exhaust system. Is there gas leakage?	Yes	Repair or replace faulty exhaust parts, then go to Step 8.
4		No	Go to the next step.
5	INSPECT INSTALLATION OF FRONT AND HO2S (REAR) Inspect for looseness of HO2S (front) and HO2S (rear). Is it normal?	Yes	Go to the next step.
5		No	Retighten sensor, then go to Step 8.
6	INSPECT HO2S (FRONT) VOLTAGE Access O2S11 PID using the WDS or equivalent. Verify PID when racing engine (in PARK or NEUTRAL). Is PID reading okay? More than 0.45 V when suddenly depressing AP (rich condition) Less than 0.45 V just after release AP (lean condition)	Yes	Go to the next step.
6		No	Replace suspected sensor, then go to Step 8.
7	CHECK TWC Remove TWC. Inspect TWC. (See THREE-WAY CATALYTIC CONVERTER (TWC) INSPECTION ) Is there any problem?	Yes	Replace TWC, then go to the next step.
7		No	Replace HO2S (rear), then go to the next step.
8	VERIFY TROUBLESHOOTING OF DTC P0420 COMPLETED Make sure to connect all disconnected connectors. Turn ignition key to ON (Engine off). Clear the DTC from the PCM memory using the WDS or equivalent. Start engine and perform DRIVE MODE except for DRIVE MODE 4. (See OBD-II DRIVE MODE ) Is same DTC present?	Yes	Replace PCM, then go to the next step.
8		No	Go to the next step.
9	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE ". (See AFTER REPAIR PROCEDURE ) Is any DTC present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE )
9		No	Troubleshooting completed.