P0433

Heated Catalyst Efficiency Below Threshold (Bank 2)

P0433 is a generic OBD-II powertrain diagnostic trouble code: Heated Catalyst Efficiency Below Threshold (Bank 2). It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0433
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P0433 means

P0433 — Heated Catalyst Efficiency Below Threshold (Bank 2) — is set when the PCM determines that a catalytic converter equipped with an electric pre-heating element on Bank 2 is not achieving adequate conversion efficiency. Electrically heated catalysts (EHC) are used on some hybrid and low-emission vehicles to accelerate catalyst light-off during cold starts by passing current through a metallic substrate before the engine produces sufficient exhaust heat. P0433 is the Bank 2 mirror of P0428 (Bank 1 heated cat efficiency).

The efficiency monitor works identically to the standard catalyst monitors: it compares upstream and downstream O2 sensor switching patterns across the heated converter. The key distinction versus P0431 (warm-up cat) is that P0433 is specifically assigned to converters that have an active electrical heating circuit. When the PCM commands the heater on but the downstream O2 sensor pattern still shows low oxygen-storage performance, P0433 is stored.

Causes may involve a failed electrical heating element — in which case the converter reaches light-off late (similar to P0431) and trips the efficiency fault — or a chemically depleted substrate that remains inefficient even with the heater functioning. On some platforms P0433 may co-occur with heater circuit codes (P0436–P0439) which should be diagnosed first.

Common causes

Most-frequently reported root causes when P0433 is logged.

  • 1
    Failed or open-circuit electrical heating element within the Bank 2 heated catalytic converter.
  • 2
    Blown fuse or relay supplying the catalyst heater on Bank 2.
  • 3
    Wiring fault in the heater power or ground circuit preventing the substrate from pre-heating.
  • 4
    Depleted or poisoned catalytic washcoat on Bank 2 that is inefficient even when the heater is operational.
  • 5
    Faulty downstream O2 sensor on Bank 2 giving a false low-efficiency signal.
  • 6
    Exhaust leak between the O2 sensors on Bank 2.
  • 7
    Engine misfire or fuel system fault causing washcoat damage over time.

Symptoms drivers notice

Malfunction Indicator Lamp (MIL) illumination.
OBD-II catalyst readiness monitor not ready — emissions test failure.
Higher cold-start emissions than normal (particularly hydrocarbons and carbon monoxide) if the heater element has failed.
May be accompanied by heated catalyst heater circuit codes (P0436, P0437, P0438, P0439) on Bank 2.
No significant driveability symptoms when efficiency is the primary fault.

How to diagnose P0433

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs — P0437/P0438/P0439 heater circuit codes on Bank 2 should be diagnosed first as a failed heater will also cause an efficiency fault.
  2. 2
    Check the heated catalyst heater fuse, relay, and wiring on Bank 2 for continuity and correct voltage supply.
  3. 3
    Measure heater element resistance at the converter connector — compare to specification (typically 0.5–5 Ω); open circuit confirms heater failure.
  4. 4
    Inspect Bank 2 downstream O2 sensor performance with live data at cruise; a switching pattern too similar to upstream indicates low converter efficiency.
  5. 5
    Check for exhaust leaks at manifold and pipe joints on Bank 2.
  6. 6
    Verify Bank 2 fuel trims are within normal range to rule out mixture-induced washcoat poisoning.
  7. 7
    If heater circuit is confirmed good and the converter substrate is depleted, converter replacement is required.

Related powertrain codes

Frequently asked questions

What is a heated catalytic converter and which vehicles use them?

A heated catalytic converter (EHC) includes an electric resistance heating element embedded in or around the metallic substrate. When energised during cold start it accelerates the converter to light-off temperature in seconds rather than minutes. EHC systems are most common on hybrid vehicles (Toyota, Honda), certain European low-emission vehicles, and some Tier 2 Bin 5 and PZEV-compliant platforms.

Should I diagnose heater circuit codes before P0433?

Yes. A failed heater element (P0436–P0439) will always result in a low efficiency code because the converter reaches operating temperature late. Repair the heater circuit first; if the efficiency code returns after the heater is working, the substrate itself is depleted.

Disabling P0433 in software

RaceTune can permanently disable P0433 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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