Faulty catalyst temperature sensor (Bank 1, Sensor 2); Sensor signal wire chafed or shorted to ground; Corroded, damaged or loose connector at the sensor; Heat damage to the wiring or loom near the exhaust; Open or high-resistance sensor reference or ground circuit; Fault in the engine control unit; Outdated control unit software that misreads the sensor signal, where the manufacturer has issued an update.

P042C

Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 2.

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
2C: FaultThe specific fault in that area

What it means

P042C is the generic code for a low input from the catalyst temperature sensor circuit on Bank 1, Sensor 2. This sensor sits downstream of the catalytic converter. The engine control unit sets the code when the signal voltage falls below the expected range, which points to a short to ground, a wiring fault or a failed sensor. Not every vehicle has this sensor, and its exact position varies by model and engine.

Symptoms

Engine management light on
No noticeable change in driving in many cases
Possible reduced performance if the car enters a protective mode
Other catalyst or oxygen sensor codes stored alongside it
Failed emissions test

Possible causes

Faulty catalyst temperature sensor (Bank 1, Sensor 2)likely
Sensor signal wire chafed or shorted to groundlikely
Corroded, damaged or loose connector at the sensorlikely
Heat damage to the wiring or loom near the exhaustpossible
Open or high-resistance sensor reference or ground circuitpossible
Fault in the engine control unitrare
Outdated control unit software that misreads the sensor signal, where the manufacturer has issued an updaterare

How to diagnose

Read all stored codes and freeze frame data, and note any related catalyst, oxygen sensor or exhaust temperature codes
Check for manufacturer service bulletins or software updates for this code on the specific model and engine
Visually inspect the sensor wiring and connector from the sensor back along the loom for chafing, melting, corrosion and water ingress
Identify the sensor position and type for the vehicle, as the layout and circuit details depend on the model and engine
Check the live data for the sensor reading with the engine cold and compare it with ambient or coolant temperature, then see whether it rises as the exhaust warms
Unplug the sensor and measure its resistance, comparing it with the manufacturer's specification
Check the signal, reference and ground circuits for continuity and for a short to ground using the wiring diagram
Clear the code and road test to confirm whether it returns

How to fix

Repair or replace damaged wiring and fix any short to ground
Clean or replace a corroded or damaged connector and its terminals
Replace the catalyst temperature sensor if it is out of specification
Repair any open or high-resistance sensor circuit
Apply a manufacturer software update if one is known to address this fault
Diagnose and repair the control unit only after the wiring and sensor are proven good

Can I keep driving?

Low severity

The car can usually be driven normally while you book it in for repair. Fix it soon so the catalyst is still monitored properly and so the car can pass an emissions test.

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