P0424
Heated Catalyst Temperature Below Threshold Bank 1.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 4
- AreaAuxiliary emission controls
- 24
- FaultThe specific fault in that area
What it means
P0424 means the engine control unit has decided that the heated catalyst on bank 1 has not reached, or has not held, the temperature it expects. This code is used on systems with an electrically or otherwise actively heated catalytic converter, and it is set when the catalyst temperature (measured or modelled) stays below the threshold for too long after start-up or during a monitoring test. Bank 1 is the side of the engine that contains cylinder number one.
Symptoms
- Malfunction indicator lamp on
- Failed emissions test
- Slightly higher fuel consumption
- Rough running or hesitation if a misfire or fuelling fault is also present
- Other catalyst or oxygen sensor codes stored alongside
Possible causes
- Faulty catalyst heating circuit, such as a heater element, relay, fuse or control output (where fitted)likely
- Damaged wiring or poor connectors in the heater or temperature sensor circuitlikely
- Faulty exhaust temperature sensor or upstream or downstream oxygen sensor giving a false readingpossible
- Secondary air injection or other warm-up strategy not working, on engines that use it to heat the catalystpossible
- Exhaust leak ahead of or near the catalyst affecting temperature or sensor readingspossible
- Degraded or failed catalytic converter that no longer lights off properlypossible
- Outdated or faulty control unit softwarerare
How to diagnose
- Read all stored and pending codes and note any related to oxygen sensors, misfires, secondary air or catalyst efficiency, as these may point to the real fault.
- Review freeze frame data for coolant temperature, engine load and run time when the code set.
- Check the relevant fuses and relays and inspect the wiring and connectors for the catalyst heater and temperature or oxygen sensors for damage, corrosion or heat damage.
- Inspect the exhaust for leaks, damage or missing heat shields from the manifold to past the catalyst.
- Using live data, compare the catalyst temperature or sensor readings with expected values during a cold start; the exact values and procedure depend on the model and engine.
- Test the heater circuit supply, earth, control signal and element resistance against the manufacturer's specification.
- If fitted, check that the secondary air system operates correctly during warm-up.
- Check for available software updates for the control unit that relate to this code for the specific vehicle.
How to fix
- Repair or replace damaged wiring, connectors, fuses or relays in the heater circuit.
- Replace a faulty catalyst heater or its control component if testing confirms a fault.
- Replace a faulty temperature sensor or oxygen sensor.
- Repair the secondary air system or other warm-up component if it is not working.
- Repair exhaust leaks.
- Replace the catalytic converter if it has failed, after the cause of any damage has been found and corrected.
- Apply a manufacturer calibration update only if an outdated or faulty calibration is confirmed as the cause.
Can I keep driving?
The car can usually be driven for a short time, but book it in soon because emissions may be higher and a failing catalyst or underlying fault could get worse. Avoid driving if there is a misfire, flashing warning lamp or loss of power.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.