Dtc P0420 - Mazda 2002 6 Workshop Manual

DTC P0420

DTC P0420 Catalyst system efficiency below threshold
• PCM compares number of front HO2S and rear HO2S inversions for a predetermined time. PCM monitors
number of inversions rear side performs while front side inverts for a specified number of times when the
following monitoring conditions are met. PCM detects inversion ratio. If inversion ratio is below threshold,
PCM determins that catalyst system has deteriorated.
MONITORING CONDITION
— Engine speed 1,410—3,000 rpm (MTX)
— Engine speed 1,281—3,000 rpm (ATX)
— Calculated load 15—50%(*
DETECTION
1
* : Maximum calculated load value varies depending on engine speed.
CONDITION
Diagnostic support note
• This is a intermittent monitor. (CATALYST)
• MIL illuminates if PCM detects the above malfunction conditions in two consecutive drive cycles or in one
drive cycle while the DTC for the same malfunction has been stored in the PCM.
• DIAGNOSTIC MONITORING TEST RESULTS and PENDING CODE are stored if PCM detects the above
malfunction condition during first drive cycle.
• FREEZE FRAME DATA is available.
• DTC is stored in the PCM memory.
• TWC deterioration or malfunction
• Exhaust gas leakage
POSSIBLE
• Looseness of front HO2S
CAUSE
• Looseness of rear HO2S
• Front HO2S malfunction
Diagnostic procedure
STEP
1 VERIFY FREEZE FRAME DATA HAS BEEN
RECORDED
• Has FREEZE FRAME DATA been recorded?
2 VERIFY RELATED SERVICE INFORMATION
AVAILABILITY
• Check for related Service Information
availability.
• Is any related Service Information available?
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 other DTCs present?
4 INSPECT GAS LEAKAGE OF EXHAUST
SYSTEM
• Visually inspect exhaust gas leakage in
exhaust system.
• Is there any gas leakage?
5 INSPECT INSTALLATION OF FRONT AND
REAR OXYGEN SENSORS
• Inspect for looseness of front and rear oxygen
sensors.
• Is it okay?
6 INSPECT TWC
• Clear DTC using WDS or equivalent generic
OBD function.
• Cycle ignition key to OFF then back to ON.
• Inspect TWC.
(See F–41 THREE-WAY CATALYTIC
CONVERTER (TWC)
• Is it okay?
ON-BOARD DIAGNOSTIC
1
)
INSPECTION
INSPECTION)
Yes Go to next step.
No Record FREEZE FRAME DATA on repair order, then go to
next step.
Yes Perform repair or diagnosis according to available Service
Information.
• If vehicle is not repaired, go to next step.
No Go to next step.
Yes Go to appropriate DTC troubleshooting.
No Go to next step.
Yes Repair or replace faulty exhaust parts, then go to Step 7.
No Go to next step.
Yes Go to next step.
No Retighten sensor, then go to Step 7.
Yes Replace suspected oxygen sensor, then go to next step.
No Replace TWC, then go to next step.
A6E397001086W02
ACTION
F–137
F