Warm Up Catalyst Efficiency Below Threshold (Bank 2)

What it means

The engine computer has detected that the warm-up catalytic converter on bank 2, the side of the engine without cylinder 1, is no longer cleaning the exhaust efficiently. This converter is designed to heat up quickly after a cold start, and the code appears on engines with two banks.

Related codes: P0430P0421P0300P0156P0174

Symptoms4

• Check engine light on, often with no other symptoms.
• Occasional sulfur smell from the exhaust.
• Power loss if the converter is clogged (less common).
• Failed emissions test.

Possible causes5

• Aged or internally damaged bank 2 warm-up catalytic converter.
• Faulty oxygen sensor after the bank 2 converter.
• Exhaust leak near the bank 2 sensors.
• Misfires or a rich mixture in bank 2 cylinders.
• Oil burning or coolant entering the exhaust.

How to diagnose5

1. Fix any bank 2 misfire or fuel mixture codes first.
2. Compare the signal of the sensor after the converter with the bank 2 upstream sensor.
3. Check the exhaust for leaks, especially at the exhaust manifold joint.
4. Confirm the downstream sensor is healthy and responsive before condemning the converter.
5. If P0421 is also stored, look for a cause shared by both banks.

How to fix5

1. Repair any exhaust leak.
2. Replace the oxygen sensor if it is proven faulty.
3. Fix the cause of misfires or oil burning.
4. Replace the bank 2 warm-up converter with a unit that meets the vehicle specification.
5. Clear the codes and drive until the converter self-test completes.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost starts with an exhaust leak repair or sensor, and rises sharply if a new converter is needed, especially one built into the exhaust manifold.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions