Damaged, chafed or heat-affected wiring to the Bank 2 catalyst temperature sensor, shorted to a voltage supply; Corroded, loose or contaminated connector at the sensor or control unit; Faulty catalyst temperature sensor (internal fault or open circuit); Open circuit in the signal or return wire causing the signal to read high; Poor or missing sensor reference ground or supply fault; Fault inside the engine control unit or sensor processing module.

P0438

Catalyst Temperature Sensor Circuit High Bank 2 Sensor 1.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
38: FaultThe specific fault in that area

What it means

P0438 is the generic code for a high input in the catalyst temperature sensor circuit on Bank 2, Sensor 1. The engine control unit saw a signal voltage from the sensor above its expected range, which usually points to a short to voltage or an open circuit that pulls the signal high. Bank 2 is the side of the engine that does not contain cylinder number one, and Sensor 1 is normally the upstream sensor. Not every vehicle has catalyst temperature sensors, and their layout varies by model and engine.

Symptoms

Engine management light on
Catalyst or emissions-related warning in some vehicles
Possible reduced power or limp mode on some models that use catalyst temperature to protect the exhaust
Failed emissions test or readiness monitors not completing
Usually no noticeable change in driveability

Possible causes

Damaged, chafed or heat-affected wiring to the Bank 2 catalyst temperature sensor, shorted to a voltage supplylikely
Corroded, loose or contaminated connector at the sensor or control unitlikely
Faulty catalyst temperature sensor (internal fault or open circuit)likely
Open circuit in the signal or return wire causing the signal to read highpossible
Poor or missing sensor reference ground or supply faultpossible
Fault inside the engine control unit or sensor processing modulerare

How to diagnose

Read all stored and pending codes and record the freeze frame data; note whether other exhaust temperature or oxygen sensor codes are present
Check the vehicle-specific information to confirm the position of Bank 2 Sensor 1 and the sensor type and wiring layout fitted to this model
Inspect the sensor wiring and connector along the exhaust for chafing, melting, corrosion, water ingress or contact with hot components
Check live data for the Bank 2 catalyst temperature reading with the engine cold and then warm; a reading stuck at the maximum or implausible value suggests a circuit fault
Unplug the sensor and measure the supply, signal and ground at the connector against the manufacturer's specification
Test the wiring for continuity, and for shorts to voltage and to ground, between the sensor and the control unit
Check the sensor resistance or output against specification, where the manufacturer provides figures
Clear the code after repair and road test to confirm it does not return and the monitors complete

How to fix

Repair or replace damaged wiring and secure it away from heat sources and sharp edges
Clean or replace corroded or damaged connectors and terminals
Replace the Bank 2 catalyst temperature sensor if it is confirmed faulty
Restore any open circuit, poor ground or supply fault found in the sensor circuit
Where all wiring and the sensor test correctly, check the manufacturer's information for control unit faults or software updates relevant to this code before considering replacement

Can I keep driving?

Low severity

The car can usually be driven while you arrange a repair, as the fault is in the sensor circuit rather than the engine itself. If the car goes into limp mode or other exhaust or catalyst faults appear, have it checked sooner.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.