Mazda MX-6 1998, Workshop Manual

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TROUBLESHOOTING [ENGINE CONTROL FS]
DTC P0420
P0421
Catalyst efficiency below threshold (Except California)
Catalyst efficiency below threshold (California)
DESCRIPTION
• DTCs P0420, P0421 indicate catalyst system efficiency is below acceptable threshold
[Possible Cause]
• Use of leaded fuel • Fuel pressure too high
• Oil contamination • Damaged exhaust system pipe
• Cylinder misfiring • Damaged exhaust manifold
• Damaged heated oxygen sensor • Damaged silencer/tailpipe component
• Damaged ECT sensor • Damaged catalytic converter
• Downstream heated oxygen sensor wires improperly
connected
Warning
Following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read following
warnings before performing fuel system service:
• Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage. Always keep sparks and flames
away from fuel.
• Fuel line spills and leaks are dangerous. Fuel can ignite and cause serious injuries or death and damage. Fuel
can also irritate skin and eyes. To prevent this, always complete “BEFORE REPAIR PROCEDURE” and “AFTER
REPAIR PROCEDURE” described in this manual.
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0 1 -1 4 BEFORE REPAIR PROCEDURE
D- 0 1 -1 4 AFTER REPAIR PROCEDURE
STEP INSPECTION ACTION
1 CHECK FOR MISFIRE MONITOR DTC
Note
• Complete the spark timing check in OBD
Test before proceeding with this step.
Spark timing retarded below specification
may increase exhaust gas temperature and
decrease catalyst efficiency overtime.
03-01-17 IGNITION SYSTEM
INSPECTION
Note
Be sure customer has not:
• Refueled vehicle with leaded gasoline.
• Experienced excessive oil consumption.
Note
• Internal deterioration of catalytic converter
is usually caused by abnormal engine
operation upstream of catalyst. Events that
may produce higher than normal
temperature in catalyst are particularly
suspect. For example, misfiring can cause
higher than normal catalyst operating
temperature higher than normal.
• Key on, engine off.
• Retrieve and record all Continuous Memory
DTCs.
• Were any of following misfire monitor
DTCs recorded: P0300, P0301, P0302,
P0303 and P0304?
Yes Go to pinpoint test for misfire DTCs.
No Go to next step.
0 1 -0 1 A -5 7