P0421 Mazda

P0421 Mazda — Diagnose and Fix

Mazda has issued a service bulletin #01-010/16 for the vehicles listed below to address a P0421 Mazda trouble code issue. The bulletin reports that some vehicles may have a check engine light along with trouble code PO421:00 (Catalytic converter system) without experiencing poor engine performance or misfire.

Mazda has determined that the ECM software is incorrectly commanding the air/fuel sensor which results in a false PO421 Warm up catalyst system efficiency below threshold. Mazda has issued a software update to correct the problem. The service bulletin also includes instruction on how to test the catalytic converter

P0421 Mazda vehicles affected by service bulletin #01-010/16

2014-15 Mazda 3 (Japan built) vehicles with VINs lower than JM1BM******267077 (produced before March 30, 2015)

2014-15 Mazda 3 (Mexico built) vehicles with VINs lower than 3MZBM******207478 (produced before April 1, 2015)

2014-16 Mazda 6 vehicles with VINs lower than JM1GJ******425952 (produced before April 8, 2015)

2014-15 CX-5 (2.5L A/T only) 2016 CX-5 vehicles with VINs lower than JM3KE******656820 (produced before April 8, 2015)

Diagnose catalytic converter and P0421 Mazda

1.Verify the condition of the Warm Up Three-Way Catalytic Converter (WU-TWC) by checking the value “Catalyst monitor bank 1” on MODE6 with M-MDS.

a. Go to Powertrain => OBD Test Modes => Mode6 On Board Test Results

b. Go to Catalyst monitor bank 1 => Equivalence Oxygen Storage Component (OBDMID. 21, Test ID: 82)

• If the value is “equal to 0”, clear the DTC and go to PCM Reprogramming.

• If the value is “equal to 2 or higher”, clear the DTC and go to PCM Reprogramming.

• If the value is “between 0 and 2”, follow these steps:

1. Clear the DTC and reprogram the PCM.

2. Disconnect the negative battery cable to clear the PCM memory (at least 1 min.)

3. Go into the “DRIVE MODE”:

a. Drive the vehicle at about 50 mph for 15min.

b. Decelerate to 25 mph, and shift into M-Mode, 3rd gear.

c. Accelerate to 40 mph while holding the transmission in 3rd gear.

d. Stay at 40 mph for 3 seconds, then release the accelerator pedal and decelerate to 25 mph.

e. Accelerate to 40 mph again while holding the transmission in 3rd gear.

f. Stay at 40 mph for 3 seconds, then release the accelerator pedal and decelerate to 25 mph again.

g. Repeat steps b-f (acceleration and deceleration) at least 10 times.

4. Check the value “Catalyst monitor bank 1” on MODE6 with M-MDS.

• If the value is “equal to 1 or higher than 1″, WU-TWC can be judged as OK.

• If the value is less than 1”, WU-TWC should be deteriorated. Refer to MS3 online instructions for DTC PO421:00 or Workshop manual section 01-01.