What Does P0425 Mean?
The PCM has detected a general circuit fault with the catalyst temperature sensor on bank 1, sensor 1 (pre-catalyst). This sensor measures exhaust gas temperature entering the catalytic converter to help the PCM evaluate converter operation and protect it from overheating. A circuit fault means the signal is missing, stuck, or outside the valid voltage range. The driver will see the MIL and the PCM may limit performance to protect the converter.
Common Causes
35%
Failed catalyst temperature sensor with open or shorted thermistor
30%
Damaged or corroded wiring at the sensor connector due to exhaust heat exposure
15%
Open 5V reference or ground circuit affecting the temperature sensor
12%
Sensor probe thermal fatigue causing element failure
8%
PCM input circuit failure for the temperature sensor
Diagnostic Steps
1
Check the catalyst temperature sensor PID on the scan tool. A reading of -40°F or an implausible fixed value indicates a circuit fault. Normal reading at operating temperature should be 600-1400°F depending on conditions.
2
Inspect the sensor connector for heat damage, melted plastic, corrosion, or disconnection. These sensors are located in the exhaust stream and connectors often suffer from extreme heat exposure.
3
Disconnect the sensor and measure thermistor resistance. At room temperature, expect 50K-200K ohms (NTC type). At exhaust operating temperature, resistance drops significantly. An open or zero reading indicates sensor failure.
4
Verify 5V reference and ground at the sensor connector with key on, engine off. If the reference is missing, check if other sensors sharing that 5V reference circuit are also affected.
5
Check wiring continuity from the sensor connector back to the PCM. Focus on areas where the harness is exposed to exhaust heat or road debris.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The PCM has detected a general circuit fault with the catalyst temperature sensor on bank 1, sensor 1 (pre-catalyst). This sensor measures exhaust gas temperature entering the catalytic converter to help the PCM evaluate converter operation and protect it from overheating. A circuit fault means the ...
The most common cause of P0425 (Catalyst Temperature Sensor (Bank 1, Sensor 1)) is: Failed catalyst temperature sensor with open or shorted thermistor
Typical repair costs for P0425 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution. Without catalyst temperature monitoring, the PCM cannot protect the converter from overheating. The PCM may enter a reduced power mode. Avoid aggressive driving, towing, or sustained high-RPM operation until the sensor is repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0425 to identify the root cause.
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Quick Info
Category
Powertrain
System
Catalytic Converter / Exhaust System
Difficulty
Type
Generic (SAE)
Recommended Tools
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