P0424: Heated Catalyst Temperature Below Threshold (Bank 1)

P0424 means the heated catalyst on Bank 1 is not getting hot enough, fast enough, after a cold start. A heated catalyst has an electric heating element that brings it to working temperature within seconds; such catalysts are still uncommon on production cars, so first check the manufacturer's definition of the code for your vehicle. Unlike P0423, which is about how well the catalyst cleans the exhaust, P0424 is about the heater not delivering enough heat, so the usual suspects are the heater element, its fuse, relay or control, and its wiring.

P0424 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0424 and illuminates the check engine light.

If your vehicle has triggered P0424, you may notice one or more of these symptoms:

• Check engine light illuminated, typically shortly after a cold start
• Higher exhaust emissions during warm-up (not usually noticeable from the driver's seat)
• Heater circuit codes (manufacturer-specific) stored alongside on some vehicles
• No change in how the car drives in most cases
• Failed emissions or periodic technical inspection

Here are the most common causes of P0424:

Generally yes, for short-term driving. Safe to drive in the short term. The heated catalyst on Bank 1 is not reaching its target temperature within the expected time after a cold start, so emissions are higher during warm-up and the car is likely to be rejected at an emissions check or periodic technical inspection. If the heater circuit has shorted, have the wiring and fuse checked promptly.

Follow these steps to pinpoint the root cause of P0424:

1. Read freeze frame and confirm the code set shortly after a cold start, which is when the heated catalyst is monitored
2. Check for heater-circuit codes (manufacturer-specific) and inspect the heater fuse and relay
3. Measure the heater element resistance and compare it with the manufacturer specification. An open circuit means the element has failed
4. Inspect the wiring harness from the heater relay to the catalyst connector for chafing, water ingress, or melted insulation near the exhaust
5. Following the manufacturer's procedure, check the heater's current draw or supply voltage during a cold start. Insufficient current points to a relay, wiring or supply fault; switching the heater on for a test needs manufacturer-level software

Repair costs for P0424 vary depending on the root cause and your vehicle. Here are typical estimates:

These codes are often seen alongside P0424 or indicate related issues: