Failed catalyst temperature sensor on bank 2, reading high resistance or open circuit; Damaged or corroded wiring between the sensor and the PCM, including a short to voltage on the signal circuit; Exhaust restriction downstream of the catalyst, such as a collapsed substrate or crushed pipe, raising actual temperature; Engine running excessively lean on bank 2 due to a vacuum leak, weak fuel pump, or dirty fuel injectors; Retarded ignition timing or incorrect camshaft timing raising exhaust gas temperature; A failing PCM driver for the sensor circuit, though this is uncommon

DTC codes / P04xx · Auxiliary emission controls / P0438

P0438Catalyst Temperature Sensor High (Bank 2)

Q: What does code P0438 mean?

Catalyst Temperature Sensor High (Bank 2). This code means the powertrain control module (PCM) has detected an abnormally high signal voltage from the catalyst temperature sensor on bank 2, which is the side of the engine that does not contain cylinder number one. The sensor is a thermistor whose resistance drops as temperature rises, so a high voltage reading tells the PCM the catalyst is running hotter than the calibration allows.

This code means the powertrain control module (PCM) has detected an abnormally high signal voltage from the catalyst temperature sensor on bank 2, which is the side of the engine that does not contain cylinder number one. The sensor is a thermistor whose resistance drops as temperature rises, so a high voltage reading tells the PCM the catalyst is running hotter than the calibration allows.

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 engine power or limp mode if the PCM decides the catalyst temperature is unsafe
A burning or sulfur-like smell from the exhaust after a drive
Poor fuel economy as the PCM adds fuel to cool the catalyst
In rare cases, a glowing red catalytic converter visible underneath the vehicle at night

Common causes, most likely first

Failed catalyst temperature sensor on bank 2, reading high resistance or open circuit
Damaged or corroded wiring between the sensor and the PCM, including a short to voltage on the signal circuit
Exhaust restriction downstream of the catalyst, such as a collapsed substrate or crushed pipe, raising actual temperature
Engine running excessively lean on bank 2 due to a vacuum leak, weak fuel pump, or dirty fuel injectors
Retarded ignition timing or incorrect camshaft timing raising exhaust gas temperature
A failing PCM driver for the sensor circuit, though this is uncommon

How to diagnose and fix it

Connect a scan tool and record the catalyst temperature sensor voltage and calculated temperature on bank 2 with the engine at operating temperature
Visually inspect the sensor, its connector, and the wiring harness for chafing, corrosion, or a loose pin
Measure resistance across the sensor terminals and compare with the manufacturer's temperature-resistance chart
Check for exhaust backpressure with a pressure gauge at the upstream oxygen sensor port to rule out a restricted catalyst
Perform a fuel trim and misfire analysis on bank 2 to confirm the engine is not running lean or misfiring
If the sensor and wiring test good, verify the signal circuit for a short to voltage with a multimeter before condemning the PCM
Replace the faulty catalyst temperature sensor or repair the wiring, clear the code, and road test to confirm the repair

What a high catalyst temperature sensor really means

A high voltage from this sensor does not automatically mean the sensor is bad; the PCM may be correctly reporting a genuinely overheated catalyst caused by an engine misfire or lean condition on bank 2.
Technicians often overlook exhaust restrictions because the vehicle may idle and rev normally in the bay, yet backpressure raises catalyst temperature only under load.
Bank 2 is the side without cylinder one, which on V6 and V8 engines is often the harder side to reach, so wiring damage from previous repairs is common there.
A catalyst temperature sensor that reads high can be caused by a poor ground at the sensor body, which adds resistance and skews the voltage the PCM sees.
Clearing the code without checking fuel trims often leads to a repeat visit, because the underlying lean condition continues to cook the converter.

Can I keep driving with P0438?

You can usually drive the vehicle to a workshop, but avoid heavy loads, towing, and sustained high-speed driving because a genuinely overheated catalyst can melt its substrate and create an exhaust restriction. If the engine runs rough or the check engine light flashes, stop driving and have it towed.

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.