What Does P042A Mean?
The PCM has detected a general circuit fault with the catalyst temperature sensor on bank 1, sensor 2 (post-catalyst). This sensor monitors the exhaust gas temperature exiting the catalytic converter to verify converter efficiency and protect it from thermal damage. A circuit malfunction means the sensor signal is absent, stuck, or outside the expected voltage range. The driver will see the MIL and the PCM may reduce power to protect the converter.
Common Causes
35%
Failed catalyst temperature sensor 2 with open or shorted thermistor element
30%
Heat-damaged or corroded wiring/connector at the post-cat sensor location
15%
Open 5V reference or ground circuit shared with other exhaust sensors
12%
Thermal fatigue failure of the sensor probe from constant heat cycling
8%
PCM input circuit failure
Diagnostic Steps
1
Check the post-cat temperature sensor PID on the scan tool. A reading of -40°F, max scale, or a fixed implausible value indicates a circuit fault.
2
Inspect the sensor 2 connector near the catalytic converter outlet. This location sees extreme heat and vibration — check for melted connector housing, corroded pins, or disconnection.
3
Disconnect the sensor and measure thermistor resistance. At room temperature (70°F), expect 50K-200K ohms depending on sensor type. An OL or 0 ohm reading indicates sensor failure.
4
Verify 5V reference voltage and ground at the sensor connector (KOEO). If the 5V reference is missing, check if other sensors on the same reference circuit are also failing.
5
If the sensor tests good, check wiring continuity from the sensor connector to the PCM. Pay close attention to areas near the catalytic converter, exhaust pipe hangers, and underbody routing where physical damage may occur.
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 2 (post-catalyst). This sensor monitors the exhaust gas temperature exiting the catalytic converter to verify converter efficiency and protect it from thermal damage. A circuit malfunction means the s...
The most common cause of P042A (Catalyst Temperature Sensor Circuit (Bank 1 Sensor 2)) is: Failed catalyst temperature sensor 2 with open or shorted thermistor element
Typical repair costs for P042A range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution. The post-catalyst temperature sensor provides critical overheating protection data. Without it, the PCM may not detect a catalyst meltdown condition. Avoid aggressive driving, towing, or extended high-RPM operation until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P042A 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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