2005 Mazda 3 • 130,000 miles


My vehicle(Mazda 3)'s engine light came on and I plugged in the OBD adapter to check and I got the messages below using an application called OBDScope. I did reset the engine light by unplugging the negative terminal of the battery and after 400km it came back on again. The car still feels fine and drives well

Any help will be appreciated.

Diagnosis by OBDSCOPE
MIL: On.
Inspection status: Failed. MIL is on.
Fuel system status: Open loop due to engine load.
Secondary air status: N/A.
Time Since Engine Start: 0s
Distance with MIL: 11km
# Of Warm-ups Since DTCs Cleared: 10
Engine Coolant Temperature: 93°C
OBD Port Voltage: 12.20V
OBD tests: 6/6 completed:
Misfire: OK
Fuel system: OK
Components: OK
Catalyst: OK
Oxygen sensor: OK
Oxygen sensor heater: OK
Lambda Tests:
Short Term Fuel Trim B1: No variation, 0.0000%
O2 Sensor B1S1: Varies between 0.0200V - 0.0250V
O2 Sensor B1S2: No variation, 0.0300V
P0420(current): Catalyst System Efficiency Below Threshold (Bank 1)
P0420(pending): Catalyst System Efficiency Below Threshold (Bank 1).
Freeze Frame:
DTC: P0420
Calculated Load: 37%
Engine Coolant Temperature: 84°C
Short Term Fuel Trim B1: 9%
Long Term Fuel Trim B1: -5%
Engine RPM: 26721/min
Vehicle Speed: 86km/h
Timing advance: 48°
Intake Air Temperature: 32°C
Air Flow Rate: 11g/s
Absolute Throttle Position: 15%
Time Since Engine Start: 822s
Commanded EGR: 46%
Commanded Evaporative Purge: 77%
# Of Warm-ups Since DTCs Cleared: 9
Distance Since DTCs Cleared: 400km
Barometric Pressure: 85kPa(a)
Catalyst Temperature B1S1: 734°C
Control Module Voltage: 14V
Absolute Load Value: 27%
Commanded Equivalence Ratio: 1
Relative Throttle Position: 5%
March 12, 2013.

P0420 Is catalyst below threshold, What you have recorded is the freeze frame when the DTC occurred, You have a lean condition, start out with a good tune up, Clean or replace the MAF sensor. Clear the code.

Mar 12, 2013.
420 is a cat code that indicates the cat is no longer working and is worn out. Replace the cat with a new one


Mar 12, 2013.
@ Randico, Thank you so much for taking your time to analyze the freeze frame because I did exactly what you suggested by cleaning the MAF sensor which was dirty and then cleared the code which has never come back. I have done about 3000 kilometers with the car ever since.

@ AseMaster6371 - Thank you for your input.
As you can see from the attached pics, the catalyst seems operating fine.

Apr 10, 2013.