MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS
TSB Revision
MULTIPORT FUEL INJECTION (MFI) <3.0L>
13B-346
DTC P0421: Warm Up Catalyst Efficiency Below Threshold (bank 1)
.
TECHNICAL DESCRIPTION
•
The signal from the rear heated oxygen sensor
differs from the front heated oxygen sensor. That
is because the catalytic converter purifies
exhaust gas. When the catalytic converter has
deteriorated, the signal from the front heated oxy-
gen sensor becomes similar to the rear heated
oxygen sensor.
•
The ECM <M/T> or PCM <A/T> compares the
output of the front and rear heated oxygen sensor
signals.
.
DTC SET CONDITIONS
Check Conditions
•
Engine speed is lower than 3,000 r/min.
•
The throttle valve is open.
•
Volume air flow sensor output frequency is
between 69 and 169 Hz.
•
More than 3 seconds have elapsed after the
abovementioned three conditions have been met.
•
Intake air temperature is higher than
−
10
°
C
(14
°
F).
•
Barometric pressure is higher than 76 kPa (11
psi).
•
Under the closed loop air/fuel ratio control.
•
Vehicle speed is 1.5 km/h (0.93 mph) or more.
•
The ECM <M/T> or PCM <A/T> monitors for this
condition for 7 cycles of 12 second each during
the drive cycle.
•
Short-term fuel trim is higher than
−
30 percent
and lower than +25 percent.
•
The cumulative volume air flow sensor output fre-
quency is higher than 4,000 Hz.
Judgment Criteria
•
The right bank heated oxygen sensor (rear) sig-
nal frequency divided by right bank heated oxy-
gen sensor (front) signal frequency = 0.8 or more.
.
TROUBLESHOOTING HINTS (The most likely
causes for this code to be set are: )
•
Right bank side catalytic converter deteriorated.
•
Right bank heated oxygen sensor failed.
•
ECM failed. <M/T>
•
PCM failed. <A/T>
DIAGNOSIS
Required Special Tool:
•
MB991502: Scan Tool (MUT-II)
STEP 1. Check the exhaust leaks.
Q: Are there any abnormalities?
YES :
Go to Step 2.
NO :
Repair it. Then go to Step 7.