A catalytic converter can wear out slowly, and the first sign is often just a check engine light. A P0433 code means the engine computer found that the heated catalyst on bank 2 is not cleaning the exhaust as well as it should.
Replacing a converter is expensive, so this guide explains how the computer tests it, what else can set the code and what to check before you buy a new one.
P0433 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 4 | Auxiliary emission controls | The fault involves emission control systems such as EGR, secondary air, EVAP or the catalytic converter. |
| 33 | Specific fault | Heated Catalyst Efficiency Below Threshold (Bank 2) |
What the P0433 Code Means
The SAE J2012 standard defines the P0433 code as Heated Catalyst Efficiency Below Threshold (Bank 2). A catalytic converter stores and releases oxygen as it cleans the exhaust. That oxygen storage is what lets it turn carbon monoxide, unburned fuel and nitrogen oxides into less harmful gases.
The powertrain control module (PCM) checks the converter by comparing the oxygen sensor before it with the sensor after it. The upstream sensor switches quickly between rich and lean. A healthy converter smooths that out, so the downstream sensor reads a fairly steady voltage, often about 0.5 to 0.8 volt. When the downstream sensor starts switching like the upstream one, the converter is no longer storing enough oxygen.
A heated catalyst has an electric heater to bring it up to working temperature quickly after a cold start. Heated catalysts are rare on road vehicles. This code means the PCM found the heated catalyst’s efficiency is too low. On some vehicles, makers use it for a converter without a heater, so check your service manual.
Bank 2 is the side of a V engine without cylinder 1. Only V6, V8 and other engines with two cylinder banks have a bank 2.
Symptoms of Low Catalyst Efficiency
Many vehicles show no symptoms at all. Common signs of a P0433 code include:
- Check engine light on
- Failed emissions test
- Sulfur or rotten egg smell from the exhaust
- Rattle from under the vehicle if the substrate is broken
- Loss of power if the converter is clogged
Because most vehicles drive normally with this code, many owners first learn about it at an emissions inspection. A clogged converter is different and can make the engine feel very weak.
Most Common Causes of the P0433 Code
The converter is often worn, but other faults can look the same to the PCM:
- Worn catalytic converter. Age and heat reduce its oxygen storage.
- Exhaust leak before the downstream sensor. Outside air makes the sensor read wrong.
- Faulty downstream oxygen sensor. A lazy or skewed sensor can set the code.
- Past misfires or rich running. Raw fuel overheats and damages the converter.
- Oil or coolant contamination. Burning oil or a head gasket leak coats the converter.
- Faulty upstream oxygen sensor or fuel control problem. The converter cannot work well if fueling is off.
Tools You Will Need
You can do most of this testing at home with basic tools:
- OBD-II scan tool that graphs both oxygen sensors
- Digital multimeter
- Infrared thermometer
- Exhaust leak detection tools, such as a smoke machine
- Mode $06 test data on your scan tool, if available
How to Track Down the P0433 Code
Fix any misfire, fuel trim or oxygen sensor codes first. A converter cannot pass its test if the engine is not running right.
Check for Other Codes and Fuel Trims
Look for misfire, lean, rich and oxygen sensor codes. Check fuel trims at idle and at 2,500 rpm. Trims beyond about plus or minus 10% point to an engine problem that should be fixed before you judge the converter.
Graph Both Oxygen Sensors
With the engine fully warm, graph the bank 2 upstream and downstream oxygen sensors at 2,000 to 2,500 rpm. The upstream sensor should switch quickly. The downstream sensor should stay fairly steady. A downstream sensor that switches almost as fast as the upstream one points to a worn converter.
Check for Exhaust Leaks
Look and listen for leaks at the manifold, flex pipe, converter flanges and the downstream sensor boss. A smoke machine finds small leaks quickly.
Even a small leak upstream of the downstream sensor can pull in air and make a good converter look bad.
Test the Downstream Sensor
Snap the throttle or add propane to make the engine run rich for a moment. A good downstream sensor should rise above about 0.8 volt. A sensor that stays low or responds slowly may be the problem.
Check Converter Temperature
With an infrared thermometer, compare the temperature just before and just after the converter on a warm engine. The outlet is often hotter than the inlet when the converter is working, but this test alone is not conclusive.
Repairs That Fix the P0433 Code
Match the repair to what your tests found. Then clear the code and drive under the same conditions that set it.
- Fix misfires and fuel control problems first.
- Repair exhaust leaks before the downstream sensor.
- Replace a faulty downstream oxygen sensor.
- Fix oil burning or coolant leaks that contaminate the converter.
- Replace the catalytic converter with an approved part if tests confirm it is worn.
After any repair, clear the code and drive normally. The catalyst monitor often needs several drives, including steady highway cruising, before it runs. Check that the monitor shows complete before an emissions test.
Common Mistakes to Avoid
These mistakes waste money or leave the real fault in place:
- Replacing the converter without fixing the misfire that killed it
- Ignoring an exhaust leak near the downstream sensor
- Using an oxygen sensor spacer or defeat device, which is illegal for road use
- Buying a converter not approved for your state
Repair Cost Breakdown
The cost to fix a P0433 code depends on the cause. This table shows typical ranges for parts and labor.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Exhaust leak repair | $10 to $100 | $100 to $350 |
| Downstream oxygen sensor | $30 to $150 | $150 to $350 |
| Aftermarket catalytic converter | $150 to $800 | $400 to $1,500 |
| OEM catalytic converter | $500 to $2,500 | $1,000 to $3,500 |
Converter prices vary a lot by vehicle. Many cars have the warm up converter built into the exhaust manifold, which raises the price. Check whether your vehicle’s emissions warranty, often 8 years or 80,000 miles on the converter in the United States, still covers it.
Is It Safe to Keep Driving with a P0433 Code?
Usually, yes, in the short term. A worn converter does not stop the engine from running, though the vehicle will fail an emissions test.
If the converter is clogged, the engine may lose power and run hot. A rattle from loose substrate or a sulfur smell are also signs to get it checked soon. Fix any misfire right away, since it can destroy a new converter.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0423 | Heated Catalyst Efficiency Below Threshold (Bank 1) |
| P0300 | Random/Multiple Cylinder Misfire Detected |
| P0156 | O2 Sensor Circuit Malfunction (Bank 2 Sensor 2) |
| P0174 | System Too Lean (Bank 2) |
| P0175 | System Too Rich (Bank 2) |
Fixing Low Catalyst Efficiency on Bank 2
A P0433 code means the PCM found the bank 2 heated catalyst is not working well enough. Worn converters are common, but exhaust leaks, bad oxygen sensors and engine problems can set it too.
- Fix misfire and fuel trim codes first.
- Graph the upstream and downstream sensors.
- Check for exhaust leaks.
- Test the downstream oxygen sensor.
- Replace the converter only after the tests point to it.
Frequently Asked Questions
Does the P0433 Code Always Mean a Bad Converter?
No. A worn converter is common, but an exhaust leak, a failing downstream oxygen sensor or an engine problem can set the same code. Test those first, since a converter is one of the most expensive exhaust parts.
Is My Converter Covered by Warranty?
In the United States, the catalytic converter is usually covered by the federal emissions warranty for 8 years or 80,000 miles, and some states require longer coverage. Check your warranty booklet or ask a dealer.
Can I Fix This Code with a Fuel Additive?
Usually not. Additives may help a converter that is slightly coated, but they cannot restore one that is worn out or damaged. Fix any engine problems, check for exhaust leaks and test the downstream oxygen sensor before replacing the converter.
Why Did My Catalytic Converter Fail?
Converters usually fail because of engine problems. Misfires send raw fuel into the converter, which overheats it. Burning oil or leaking coolant coats it. Running rich for a long time can also damage it. Fix the cause, or a new converter may fail too.
Will an Aftermarket Converter Work?
It depends on where you live. Some states, including California, require CARB-approved converters. A cheap converter may not store enough oxygen and the code can return. Use a converter approved for your vehicle and location.