2000 Mitsubishi Galant EMISSIONS TEST

CANDIDA

MEMBER
2000 MITSUBISHI GALANT
6 CYL
FWD
AUTOMATIC
140,000 MILES

I WENT TO TAKE MY EMISSIONS TEST TODAY AND I FAILED, ON THE PAPER IT STATES TROUBLE CODE PO421, WHAT DO I NEED TO FIX IN ORDER TO PASS EMISSIONS TEST FOR WHAT PART IS THIS CODE FOR, CATYLIST, O2 SENSOR, I HAVE NO CLUE AND IF ANY ONE CAN LET ME KNOW WHAT PART I NEED TO PUT ON TO PASS THE TEST I WOULD GREATLY APPRECIATE IT?

1 Reply

KHLOW2008

MECHANIC
41,814 POSTS

Hi CANDIDA,

Thank you for the donation.

Here are the diagnostics for the trouble code.

DTC P0421 : WARM-UP CATALYTIC CONVERTER EFFICIENCY BELOW THRESHOLD (CALIFORNIA)

NOTE:
DTC P0421 applies to warm-up catalytic converter on right bank (bank 1) of vehicles.

DTC Set Criteria
DTC will set under following conditions:
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Engine speed is less than 3000 RPM. Volume Airflow (VAF) sensor output frequency is 69-169 Hz. Intake air temperature is more than 14 °F (-10 °C). Barometric pressure is more than 11 psi (76 kPa). Throttle valve is open. Engine is in closed loop control. Vehicle speed is one MPH or more. Code will set if rear Heated Oxygen Sensor (HO2S) signal becomes similar to front HO2S signal.

Probable Causes
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Catalytic converter deteriorated.
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HO2S failed.
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Engine Control Module/Powertrain Control Module (ECM/PCM) failed.

Diagnostic Procedure

1. Check right bank exhaust manifold and front exhaust pipe for cracks. If problem exists, replace manifold or front exhaust pipe as necessary, then go
to step 7. If problem does not exist, go to next step.

2.Connect scan tool to OBD-II Data Link Connector (OBD-II DLC). Using scan tool, check data list item No. 59 (rear heated oxygen sensor). Warm-up engine. Drive vehicle in Low (A/T) or 2nd gear (M/T) at wide open throttle. Rear HO2S output voltage should be 600-1000 millivolts. If voltage is as pecified, to to next step. If voltage is not as specified, check appropriate rear Heated Oxygen Sensor (HO2S) circuit.

3.Using scan tool, check data list item No. 11 (front heated oxygen sensor). Monitor front HO2S output voltage when engine is suddenly decelerated from about 4000 RPM. Voltage should increase from less than 200 millivolts to more than 600 millivolts within a few seconds. If voltage is as specified, go to next step. If voltage is not as specified, check front HO2S circuit.

4.Hold engine speed at 2000 RPM and monitor front HO2S output voltage. Scan tool reading should alternate between 400 millivolts or less and 600 millivolts or more at least 5 times within 10 seconds. If voltage switches as specified, replace rear HO2S, then go to next step. If voltage does not switch as specified, replace appropriate front HO2S, then go to step 7 .

5.Test drive vehicle following OBD-II drive cycle catalytic converter monitor pattern. See OBD-II DRIVE CYCLES Check for DTCs. If DTC P0421 is output, replace catalytic converter, then go to next step. If DTC P0421 is not output, inspection is complete.

6.Test drive vehicle following OBD-II drive cycle catalytic converter monitor pattern. Check for DTCs. If DTC P0421 is output, replace ECM/PCM, then go to next step. If DTC P0421 is not output, inspection is complete.

7.Test drive vehicle following OBD-II drive cycle catalytic converter monitor pattern. Check for DTCs. Confirm DTC does not reset.

OBD-II DRIVE CYCLES

Catalytic Converter Monitor
This monitor applies to DTCs P0420, P0421 and P0431. Following conditions must be met during the test:
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Atmospheric temperature is 14 °F (-10 °C) or more.
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A/C switch is in OFF position.
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If automatic transmission, selector lever is in "D" range.
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If applicable, overdrive switch is in ON position.
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If applicable, pattern select switch is in OFF position.

Monitor takes about 20 minutes to complete. To run monitor, use illustration. See Fig. 1. Perform steps as follows:

1.Remove all test equipment from vehicle and install all components and connectors that were removed or disconnected during testing.

2.Start engine.

3.Accelerate to 45 MPH.

4.Travel 300 seconds or more while keeping speed at 45-60 MPH (M/T: 5th gear).

5.Decelerate to 35-40 MPH.

6.While keeping accelerator pedal opening degree constant, keep speed at 35-40 MPH for 90 seconds or more (M/T: 4th gear).

7.Fully close throttle and decelerate for 10 seconds. Then, quickly accelerate until speed is 35-40 MPH. Then repeat steps 5) and 6) five more times.

8.Return vehicle to shop and turn ignition off.

9.Confirm DTC is not output. If DTC is output, go to appropriate DTC test in appropriate SELF-DIAGNOSTICS article.