OBD-II trouble code
P0433: Heated Catalyst Efficiency Below Threshold (Bank 2)
The heated-catalyst efficiency monitor on bank 2 is below threshold. Bank 2 is the bank that does not contain cylinder 1. The wiring diagram shows whether an electric heater is fitted. Comparing the two banks separates a fault on this bank from a cause both banks share.
Quick facts
- System
- Powertrain
- Category
- Emissions / Catalyst
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $200 – $2,500
- DIY difficulty
- Intermediate DIY
Browse every code in P0400–P0499, or start from the full code library.
What does P0433 mean?
P0433 is the heated-catalyst efficiency code for bank 2, the bank that does not contain cylinder 1. An inline engine with one exhaust bank does not set it. A stored P0433 on that engine is a reason to recheck the code definition and the wiring, not to search for a second bank. Where the upstream sensor switches, the monitor compares that swing with a downstream sensor that should stay nearly flat behind a healthy catalyst. A wideband upstream sensor does not switch. When the bank-2 rear sensor begins to mirror its upstream partner, the PCM judges that catalyst's oxygen-storage capacity has fallen too low and sets P0433. The word heated in the title is not proof an electric heater is fitted. The wiring diagram decides. Where a heater is shown, that circuit is tested before the converter is condemned. Bosch patent US6550236 describes three-way operation above approximately 250°C. A switching downstream sensor that copies the upstream swing is the pattern a failed oxygen-storage monitor uses. A wideband upstream sensor does not switch, and that engine's monitor is the one in its service information.
The causes mirror the rest of the catalyst family: an aged or contaminated converter, a lazy or biased downstream O2 sensor, an exhaust leak near the rear sensor, an upstream misfire or rich condition that cooked the substrate, or — on a true heated-catalyst system — a fault in that bank's catalyst heater circuit. What makes a bank-specific code useful is the ability to compare banks. If only bank 2 is flagged while bank 1's monitor passes, the problem is localized to bank 2's converter, its downstream sensor, or its exhaust section. If both banks read low, suspicion shifts toward a shared cause — a fuel-system or engine-wide condition feeding both sides rich, or oil/coolant consumption affecting both converters.
The efficiency fault itself does not change how the engine runs. An OBD inspection that uses the lamp will not pass while the code is stored. Power loss is checked as a restricted or breaking substrate, which is a different failure. Diagnosis follows the family playbook — clear misfires and fuel-trim faults, verify the bank-2 downstream O2 sensor, check for exhaust leaks, and confirm the heater circuit if equipped — all focused specifically on the bank-2 side of the exhaust.
Common causes
- Lazy or biased bank-2 downstream oxygen sensor faking a low reading
- Exhaust leak near the bank-2 rear O2 sensor
- Misfire on a bank-2 cylinder sending raw fuel into that catalyst
- Rich-running condition overheating the bank-2 converter
- Catalyst heater circuit fault on the bank-2 converter where equipped
- Oil or coolant contamination poisoning the substrate
- Degraded bank-2 catalytic converter with reduced oxygen-storage capacity — the expensive answer, and the one to reach last
Symptoms
- Check engine light with P0433 stored
- No drivability change from the efficiency fault itself
- Failed emissions or smog inspection
- Compared with the bank 1 catalyst monitor on the same drive
- Reduced power only if the bank-2 converter substrate is breaking up
- May appear with P0430 or other bank-2 codes
Diagnostic steps
- 1.Confirm the engine has two banks — a single-bank engine cannot set P0433, so a stored code on such a vehicle points to a wiring or definition error.
- 2.Identify which physical side is bank 2 (the side without cylinder number one) for the specific engine before testing anything.
- 3.Scan for bank-2 misfire or fuel-trim codes and fix them first, since they damage that catalyst.
- 4.Compare bank-1 and bank-2 O2 sensor data — a problem isolated to bank 2 localizes the fault; both banks low suggests a shared cause.
- 5.Inspect the bank-2 exhaust for leaks near the rear O2 sensor and verify that sensor is responsive.
- 6.If a heated catalyst is used, check the bank-2 heater circuit before considering converter replacement.
Repair cost
$200 – $2,500
Read the printed bracket as a planning span, not a quoted price. The low end names the bank 2 downstream oxygen sensor, an exhaust leak, or the heater fuse when the diagram shows a heater. The high end names the bank 2 catalyst. Repair a misfire or a rich condition stored with this code before a new catalyst is installed.
Estimate your repair
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Open the Repair Cost Estimator with catalytic converter replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.