A P0420 diagnostic trouble code (DTC) on a Mitsubishi Outlander indicates “Catalyst System Efficiency Below Threshold (Bank 1).” This means the catalytic converter isn’t performing as efficiently as expected. The catalytic converter has two oxygen sensors: one upstream (before the converter) and one downstream (after). The upstream sensor readings should fluctuate, while the downstream sensor should remain relatively steady. A P0420 code is triggered when the readings from both sensors are too similar, suggesting the converter isn’t effectively reducing harmful emissions.
Several factors can contribute to a P0420 code in a Mitsubishi Outlander:
- Faulty Oxygen Sensor: A malfunctioning oxygen sensor can provide inaccurate readings, triggering the P0420 code. This could be either the upstream or downstream sensor. Replacing the faulty sensor is often the solution.
- Damaged Catalytic Converter: A physically damaged or internally failing catalytic converter is a common cause of this code. Cracks, clogs, or melted components within the converter can restrict flow and reduce efficiency. Replacement is usually necessary.
- Exhaust Leaks: Leaks in the exhaust system, particularly before the catalytic converter, can introduce excess oxygen and disrupt the sensor readings. Repairing any leaks is crucial.
- Engine Misfires: Misfires can send unburnt fuel into the exhaust system, overwhelming the catalytic converter and potentially damaging it. Addressing the underlying misfire issue is paramount.
- Rich Fuel Mixture: A fuel mixture that’s too rich (excessive fuel compared to air) can overload the catalytic converter. This can be caused by faulty fuel injectors, a malfunctioning mass airflow sensor, or other fuel system issues.
- Leaded Fuel: While less common in modern vehicles, using leaded fuel in an engine designed for unleaded fuel can poison the catalytic converter, rendering it ineffective.
- Engine Coolant Temperature Sensor Issues: An incorrect engine temperature reading can affect the engine’s air-fuel ratio and catalytic converter performance. A faulty coolant temperature sensor might contribute to the P0420 code.
- Retarded Spark Timing: Incorrect spark timing can lead to incomplete combustion, sending unburnt fuel to the catalytic converter and causing it to overheat and potentially fail.
Solving a P0420 code requires a systematic diagnostic approach. Start by inspecting the exhaust system for leaks. Next, check the operation of the oxygen sensors. Using a diagnostic scanner to monitor live data from the sensors can help pinpoint the problem. If the sensors are functioning correctly and there are no leaks, the catalytic converter itself may need replacement. Remember, addressing underlying issues like misfires or a rich fuel mixture is essential to prevent future P0420 codes. Ignoring this code can lead to decreased fuel economy, increased emissions, and potential damage to other components. Consult a qualified mechanic for accurate diagnosis and repair.
