Fault code P0426 – a step-by-step guide to diagnosing and fixing it

Error code P0426 is displayed and the check engine light is on - what does this mean?

DTC P0426 is detected by the OBD system when the catalytic converter temperature is too low and the system detects insufficient heating of the catalytic converter. This error code relates to the exhaust gas purification system and can occur with different manufacturers, although the exact definition may vary slightly depending on the vehicle manufacturer.

What can cause this fault code?

• Defective or inefficient catalytic converter
• Faulty lambda sensors before or after the catalytic converter
• Defective catalytic converter heater
• Damaged cable connections to the catalytic converter heater
• Defective engine control unit (ECU)
• Leaking exhaust system upstream of the catalytic converter
• Dirty or blocked exhaust pipes
• Faulty temperature sensors in the exhaust system
• Problems with the fuel injection system
• Loose or corroded plug connections

What symptoms occur in parallel with fault code P0426?

• Increased exhaust emissions: The vehicle produces more pollutants than permitted
• Poor engine performance: Reduced power and sluggish acceleration
• Increased fuel consumption: The engine works less efficiently
• Starting problems: Starting difficulties can occur, especially when the engine is cold
• Uneven idling: The engine runs unevenly at idle speed
• Unpleasant odors: Unburnt fuel vapors may be perceptible

How can the problem with error code P0426 be rectified?

• Repairing EOBD error code P0426 requires a systematic diagnosis of the exhaust gas purification system.
• Completely replace the catalytic converter and check the exhaust system for leaks
• Replace and calibrate the lambda sensors before and after the catalytic converter
• Completely replace the catalytic converter heater including wiring and fuses
• Replace temperature sensors in the exhaust system and check measured values
• Reprogram engine control unit or replace completely if defective
• Clean exhaust system, seal leaks and replace fastenings
• Clean fuel injection system, check injectors and replace if necessary