P0424
Heated Catalyst Temperature Below Threshold (Bank 1)P0424 is a generic OBD-II powertrain diagnostic trouble code: Heated Catalyst Temperature Below Threshold (Bank 1). 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.
What P0424 means
P0424 — "Heated Catalyst Temperature Below Threshold (Bank 1)" — is stored when the PCM determines that the bank 1 heated catalytic converter has not reached the minimum expected temperature during the monitored evaluation window. Unlike P0423 (which assesses conversion efficiency via O2 sensor cross-comparison), P0424 directly measures whether the catalyst assembly is achieving the thermal threshold the PCM expects — typically detected via one or more exhaust gas temperature (EGT) sensors positioned at the catalyst inlet and/or outlet, or via a dedicated temperature sensor integrated into the heated catalyst assembly.
A heated catalytic converter incorporates an electric resistance heater (powered from the vehicle's electrical system during cold start) that rapidly brings the precious metal substrate to light-off temperature — typically above 250–300 °C — before exhaust gas temperature alone would achieve this. This is critical on cold-start-sensitive applications where the majority of a trip's total emissions are produced in the first 60–90 seconds after a cold start. P0424 is triggered when the PCM commands the heater on and the temperature sensor(s) do not confirm the expected temperature rise within the allowed time. This points to a failed heater element (open circuit, blown fuse, failed relay), a severely degraded catalyst with insufficient thermal mass to retain heat, or a faulty temperature sensor reporting a falsely cold reading. P0424 may appear alongside P0423 if the heater failure is also causing an efficiency failure, or in isolation if the efficiency monitor has not yet evaluated the cold efficiency but the temperature fault is already confirmed. This code is most commonly seen on diesel engines with electrically-heated catalyst assemblies and on certain early hybrid platforms.
Common causes
Most-frequently reported root causes when P0424 is logged.
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1
Failed electric heater element within the heated catalyst assembly — open circuit preventing the heater from generating heat.
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2
Blown fuse or failed relay in the heater element power supply circuit.
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3
Open circuit or high-resistance fault in the heater element wiring harness or connector.
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4
Faulty exhaust gas temperature sensor or catalyst temperature sensor reporting a falsely low temperature.
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5
Degraded or internally damaged catalyst substrate with insufficient thermal mass to retain heat and register the expected temperature rise.
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6
PCM heater control output fault not energising the heater relay.
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7
Severely contaminated catalyst (oil, coolant, or soot) reducing thermal conductivity and heat retention.
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8
Short to ground in the heater element circuit causing the element to draw insufficient current for adequate heating.
Symptoms drivers notice
How to diagnose P0424
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scan tool and retrieve all stored and pending codes; note whether P0423 (efficiency) is also stored, and check for EGT sensor codes that might indicate a faulty temperature sensor triggering a false P0424.
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2
Inspect the heater element fuse and relay — a blown fuse is the simplest and most common cause; replace and monitor for recurrence (repeated blown fuses indicate an overcurrent fault in the heater winding or wiring).
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3
Measure the heater element resistance at the catalyst assembly connector (key off, connector unplugged) — a healthy element typically reads 1–5 ohms; open circuit (OL) indicates a failed heater element.
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4
Verify supply voltage and ground at the heater element connector with the key on and heater relay commanded on — absent voltage with a good fuse and relay indicates a wiring open or PCM output fault.
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5
Check the exhaust gas temperature or catalyst temperature sensor reading on live data — compare against ambient temperature on a cold start; a sensor reading far above ambient before the heater has operated suggests a faulty sensor.
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6
Inspect the catalyst assembly for physical damage, contamination, or evidence of substrate collapse that would reduce thermal performance.
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7
If heater circuit and sensors are confirmed good but the temperature threshold is still not reached, the catalyst assembly itself has degraded thermally and requires replacement.
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
What is the difference between P0423 and P0424?
P0423 is an efficiency code — the PCM compares upstream and downstream O2 sensor activity and determines the catalyst is not converting pollutants adequately, regardless of temperature. P0424 is a temperature code — the PCM checks a dedicated temperature sensor and determines the catalyst body is not reaching the expected thermal level. A failed heater element typically sets P0424 first; if the efficiency monitor subsequently evaluates the cold catalyst and fails it, P0423 follows. Both can appear together.
Can a bad EGT sensor cause P0424 on an otherwise healthy heated catalyst?
Yes. If the exhaust gas temperature sensor or catalyst temperature sensor is faulty and reports a lower temperature than actual, the PCM will believe the catalyst is not reaching threshold and set P0424 even if the heater element is functioning correctly. Always verify sensor plausibility before condemning the catalyst assembly.
Is P0424 more common on diesel or petrol engines?
P0424 is predominantly associated with diesel engines equipped with electrically-heated catalyst or NOx trap assemblies (common on Euro 5/6 light diesel platforms), though it also appears on some petrol hybrid applications. It is rarely seen on conventional non-hybrid petrol engines, which typically do not use electrically-heated catalysts.
Will the engine go into limp mode with P0424?
In most calibrations, no — P0424 is a catalyst monitoring fault and does not trigger limp mode or torque reduction on its own. The engine will run normally once warm. However, on some emissions-critical diesel platforms with strict deNOx management, a confirmed catalyst thermal fault may trigger a warning and eventually a regeneration inhibit or derating if left unrepaired.
Disabling P0424 in software
RaceTune can permanently disable P0424 — 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.
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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