Faulty catalyst temperature sensor (bank 1) sending an out-of-range or erratic signal; Damaged or corroded wiring or connector at the sensor or PCM; Exhaust leaks before the sensor allowing outside air to skew temperature readings; Aging or contaminated catalytic converter causing actual temperature deviations; PCM software calibration issue or internal fault in the temperature sensing circuit; Engine misfire or rich condition raising exhaust temperatures beyond normal range

DTC codes / P04xx · Auxiliary emission controls / P0426

P0426Catalyst Temperature Sensor Range/Performance (Bank 1)

Q: What does code P0426 mean?

Catalyst Temperature Sensor Range/Performance (Bank 1). P0426 means the powertrain control module (PCM) has detected that the bank 1 catalyst temperature sensor is not reporting a plausible temperature range or is not responding as expected during monitored conditions. The PCM compares the sensor signal against modeled exhaust temperatures and other sensor inputs, and when the signal falls outside the expected range or fails a performance check, it stores this code and illuminates the check engine light.

P0426 means the powertrain control module (PCM) has detected that the bank 1 catalyst temperature sensor is not reporting a plausible temperature range or is not responding as expected during monitored conditions. The PCM compares the sensor signal against modeled exhaust temperatures and other sensor inputs, and when the signal falls outside the expected range or fails a performance check, it stores this code and illuminates the check engine light.

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
A slight decrease in fuel economy as the PCM may enrich the mixture to protect the catalyst
Intermittent or erratic temperature gauge readings if the sensor signal is unstable
Possible rough running or hesitation during cold starts if the PCM misjudges catalyst temperature
Failed emissions test due to the stored code and potential catalyst monitor incompletion
In rare cases, a burning or sulfur smell from the exhaust if the catalyst overheats

Common causes, most likely first

Faulty catalyst temperature sensor (bank 1) sending an out-of-range or erratic signal
Damaged or corroded wiring or connector at the sensor or PCM
Exhaust leaks before the sensor allowing outside air to skew temperature readings
Aging or contaminated catalytic converter causing actual temperature deviations
PCM software calibration issue or internal fault in the temperature sensing circuit
Engine misfire or rich condition raising exhaust temperatures beyond normal range

How to diagnose and fix it

Connect a scan tool and record freeze-frame data and any pending codes to understand when the fault occurs
Visually inspect the bank 1 catalyst temperature sensor, its wiring, and connector for damage, corrosion, or loose pins
Check for exhaust leaks upstream of the sensor using a smoke machine or by listening for ticking noises
Measure the sensor resistance and compare it to the manufacturer's specification across temperature changes
Backprobe the sensor signal circuit at the PCM and compare live data to a known-good value or substitute a known-good sensor
Verify that the catalytic converter is not restricted or contaminated by checking backpressure and inspecting for physical damage
After repairs, clear codes and complete a drive cycle to confirm the monitor runs and the code does not return

What the catalyst temperature sensor really monitors

The catalyst temperature sensor is often confused with the oxygen sensor, but it specifically measures the temperature inside the catalytic converter to protect it from overheating damage.
A P0426 can be set by a lazy sensor that responds slowly rather than failing completely, so live data graphing during a test drive is more revealing than a simple resistance check.
Exhaust leaks upstream of the sensor are a commonly missed cause because they can dilute the exhaust sample and make the sensor report a lower-than-actual temperature.
Replacing the catalytic converter without first verifying the sensor and wiring is an expensive misdiagnosis, as the code often stems from the sensor circuit rather than the converter itself.
On some vehicles, a weak battery or charging system issue can cause voltage drops that affect the sensor reference signal and trigger this code intermittently.

Can I keep driving with P0426?

You can usually continue driving with P0426, but avoid heavy acceleration or sustained high-speed driving that could raise exhaust temperatures further. Have the fault diagnosed soon, because ignoring it may lead to catalyst damage and a more expensive repair.

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.