Faulty catalyst temperature sensor (bank 1 sensor 2) due to internal failure or contamination; Damaged or corroded wiring harness or connector at the sensor; Exhaust leaks upstream of the sensor causing temperature fluctuations; Catalytic converter degradation or overheating that alters the temperature profile; PCM software calibration issue or internal driver fault; Poor electrical ground connection for the sensor circuit

DTC codes / P04xx · Auxiliary emission controls / P042B

P042BCatalyst Temperature Sensor Circuit Range/Performance Bank 1 Sensor 2

P042B indicates that the powertrain control module (PCM) has detected an out-of-range or erratic signal from the catalyst temperature sensor located after the catalytic converter on bank 1. The sensor's voltage or resistance does not correlate with expected exhaust temperature behavior during normal engine operation, triggering the range/performance fault.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced fuel economy as the PCM may alter fuel trim to protect the catalyst
Intermittent or constant rough running if the faulty sensor signal affects other calculations
A failed emissions test due to the stored trouble code
Possible hesitation or lack of power under certain load conditions

Common causes, most likely first

Faulty catalyst temperature sensor (bank 1 sensor 2) due to internal failure or contamination
Damaged or corroded wiring harness or connector at the sensor
Exhaust leaks upstream of the sensor causing temperature fluctuations
Catalytic converter degradation or overheating that alters the temperature profile
PCM software calibration issue or internal driver fault
Poor electrical ground connection for the sensor circuit

How to diagnose and fix it

Use an OBD-II scanner to verify the code and check live data for the catalyst temperature sensor reading
Visually inspect the sensor, wiring, and connector for damage, corrosion, or loose pins
Check for exhaust leaks around the catalytic converter and upstream piping
Measure the sensor's resistance and compare to manufacturer specifications
Test the sensor circuit for continuity and voltage drops to rule out wiring faults
Replace the catalyst temperature sensor if testing confirms it is out of specification
Clear the code and perform a drive cycle to verify the repair and ensure the code does not return

Before you replace the catalytic converter

A contaminated or failing catalyst temperature sensor can mimic a failing catalytic converter, so always test the sensor before condemning the converter.
Exhaust leaks upstream of the sensor are a common cause of erratic temperature readings that set P042B, yet they are often overlooked during diagnosis.
The PCM may set this code due to a poor ground connection rather than a faulty sensor, so checking ground integrity is a critical step.
On some vehicles, a software update for the PCM can correct false P042B triggers without any hardware replacement.
The catalyst temperature sensor is used to protect the converter from overheating, so ignoring the code can lead to costly converter damage over time.

Can I keep driving with P042B?

You can generally continue driving with P042B, but avoid heavy loads or aggressive driving that could overheat the catalytic converter. Have the fault diagnosed promptly to prevent potential converter damage and to ensure the vehicle passes emissions testing.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.