1998 Kia Sophia fixed problem, engine light still comes on.

Hi starfoxx,

Thank you for the donation.

DTC P0422: CATALYST EFFICIENCY BELOW THRESHOLD
Diagnostic Aids
ECM evaluates catalytic converter storage capability by monitoring upstream Heated Oxygen Sensor (HO2S) and downstream HO2S performance, calculating a ratio based on the amplitude of the 2 signals and evaluating this information based on load and speed conditions. Code will set when ECM determines catalytic converter storage capability has degraded. Monitor runs continuously. Two trip fault.

Check for:
Insufficient engine combustion.
Intake system or exhaust system air leak.
Improper fuel pressure.
Damaged Three Way Catalytic (TWC) converter.

Procedure
NOTE: Indication of a good catalytic converter is front HO2S output voltage switches normally while rear HO2S output remains fairly flat. Indication of a weak catalytic converter is front HO2S output voltage switches normally and rear HO2S output voltage pattern is a lower amplitude imitation of the front HO2S.

I would suggest getting a diagnostic reading of the front and rear HO2S. Aftermarket items sometimes do not work as well as they should and it could be the wiring/installation of the HO2S sensors.

Hi,

The question is open till you are satisfied and you are always welcomed back anytime.

Autozone do have a tools loan program and if you are into DIY, maybe you can enquire and get the necessary tools for the testing/diagnosis. We at 2carpros. Com would be most willing to assist in whatever way we can.

Direct fit O2 sensor should be ok as there is no possibility or wrongly spliced wires. However generic parts sometimes do not go well with some vehicles as the rating might be different. Further test would be necessary to find out.

Hi,

Yes, fuel delivery and pressure is one of the possible causes of P0422 and apart from vacumn leakages, exhaust leakages would cause it too. however it shold be noted that the cleaning might not fully clear clogged injectors.

Was exhaust checked for leakages between exhaust manifold and catalytic converter?

Here are some testing procedures that you can carry out.

1. Perform fuel pressure test, maximum fuel pressure test and fuel pressure hold test. If fuel pressure tests are within specifications, go to next step. If any fuel pressure test is not within specification, repair fuel system as necessary.

2. Perform fuel injector inspection and volume test. If all fuel injectors are operating properly, go to next step. If any fuel injector is not operating properly, repair appropriate fuel injector.

3. Check vacuum hoses for leaks. Check purge solenoid valve for proper installation and operation. If problem exists, repair as necessary. If problem does not exist, go to next step.

4. Backprobe and monitor voltage between front HO2S connector terminal No. 4 (Green/Brown wire) and ground. See Fig. 8 . Start engine and allow it to warm-up to normal operating temperature. With engine idling, spray short spurts of aerosol carburetor cleaner into following areas while observing voltage changes:
Throttle body gasket.
Gasket between intake manifold and cylinder head.
Gasket between intake manifold and surge tank.
Seals between intake manifold and fuel injectors.
Seal between surge tank and PCV pipe.

A long rise in voltage that corresponds to approximate timing and duration of spray of carburetor cleaner indicates air leak in area sprayed. If leak is indicated, repair leak as necessary. If no leak is indicated, go to next step.

5. With engine idling, have helper hold wadded rag against tailpipe. Listen for exhaust leaks between main catalytic converter and cylinder head. If exhaust leak is detected, repair as necessary.