P1425 Catalyst Temperature Sensor Circuit
The P1425 code indicates that the Powertrain Control Module (PCM) has detected a fault in the catalyst temperature sensor circuit, typically for Bank 1. This sensor is a negative temperature coefficient (NTC) thermistor that monitors the catalytic substrate temperature to prevent overheating and optimize fuel injection during cold starts or regeneration events. The fault is triggered when the voltage signal is out of the calibrated range (open circuit, short to ground, or short to battery) or when the reading is irrational compared to other exhaust temperature sensors.
01. Most Common Causes
- Faulty catalyst temperature sensor (EGT/TWC) with internal open or short circuit
- Damaged, corroded, heat-melted, or shorted wiring or connectors
- Exhaust leak upstream of the sensor causing false low readings due to cooling
- Internal PCM failure (rare)
- Aftermarket exhaust without proper sensor bung or incorrect sensor installed
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Possible reduced fuel economy or performance
03. Step-by-Step Diagnosis
Scan for codes and verify P1425 is present
Visually inspect the sensor wiring and connector for damage, corrosion, or melting
Check for exhaust leaks upstream of the sensor
Test sensor resistance and compare to specifications (NTC type)
If wiring and sensor check out, test PCM output signals
1. Frequently Asked Questions
Is it safe to drive?▼
Yes, but it is recommended to diagnose and repair soon to avoid potential catalyst damage or reduced efficiency.
How much does it cost to fix?▼
Typically $150 to $400 for parts and labor, depending on sensor location and vehicle.