P0426

What it means

P0426 is the generic SAE J2012 code for a range or performance fault with the catalyst temperature sensor on Bank 1, Sensor 1. The engine control unit compares the sensor's reading with the temperature it expects from the engine load, exhaust conditions and running time. If the signal is implausible, stuck, or fails to follow expected changes, the code is set. Few vehicles use catalyst temperature sensors, so the layout and sensor position depend on the model and engine.

Symptoms

• Malfunction indicator lamp on
• Usually no change in how the car drives
• Possible catalyst efficiency or other emissions-related codes stored alongside
• Possible failed emissions test
• Occasionally reduced performance if the control unit applies a protective strategy

Possible causes

• Faulty catalyst temperature sensor giving a drifting, stuck or implausible readinglikely
• Damaged, chafed or heat-affected wiring or connector to the sensorlikely
• Corrosion or poor contact in the sensor connector terminalspossible
• Exhaust leak near the sensor affecting the temperature readingpossible
• Underlying engine fault such as misfire or over-rich running causing abnormal catalyst temperaturespossible
• Degraded or overheated catalytic converter changing the expected temperature behaviourrare
• Fault in the engine control unit or outdated softwarerare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, looking for misfire, fuel trim or catalyst efficiency codes that point to an underlying fault
2. Check for technical service bulletins or software updates relating to this code for the specific model and engine
3. Visually inspect the sensor, its wiring and connector for heat damage, chafing, corrosion or water ingress
4. Check the exhaust around the sensor for leaks, damage or loose joints
5. Using live data, compare the catalyst temperature reading with a cold engine, then warm, and note whether it rises plausibly and in line with exhaust conditions
6. Check the sensor's wiring for continuity, shorts and voltage drop using the manufacturer's wiring diagram, and test the sensor against its specification
7. Check that the engine runs correctly, including fuel trims and no misfire, before condemning the sensor or catalyst
8. Clear the code and road test, then recheck to confirm the fault does not return

How to fix

• Repair or replace damaged wiring and clean or replace the faulty connector
• Replace the catalyst temperature sensor if it is out of specification or giving an implausible reading
• Repair any exhaust leak affecting the sensor area
• Fix any underlying engine fault, such as misfire or incorrect fuelling, that is causing abnormal catalyst temperatures
• Replace the catalytic converter only if testing confirms it is damaged or failed
• Apply a software update only where the manufacturer lists an outdated calibration as a known cause

Can I keep driving?

Nearby codes

• P0425GenericCatalyst Temperature Sensor Circuit Bank 1 Sensor 1
• P0427GenericCatalyst Temperature Sensor Circuit Low Bank 1 Sensor 1