Damaged, chafed or heat-affected wiring to the sensor, causing a short to voltage or open circuit; Corroded, loose or contaminated connector at the sensor or control unit; Faulty catalyst temperature sensor (internal failure); Genuinely overheated catalytic converter from misfire or rich running; Fault in the sensor's reference or supply voltage, such as a short to a supply wire in the harness; Faulty engine control unit or its sensor input circuit.

P042D

Catalyst Temperature Sensor Circuit High Bank 1 Sensor 2.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
2D: FaultThe specific fault in that area

What it means

P042D is the generic code for a high input fault in the catalyst temperature sensor circuit on Bank 1, Sensor 2, which is the sensor located downstream of the catalytic converter. The engine control unit saw a signal voltage above the expected range, usually a short to voltage or an open circuit that pulls the signal high. The control unit can no longer trust the temperature reading, so it logs the fault and may limit related monitoring.

Symptoms

Engine warning light on
Little or no change in how the engine drives
Possible reduced power or limp mode on some models
Other catalyst or emissions monitors not completing
Failed emissions test or MOT readiness status not set

Possible causes

Damaged, chafed or heat-affected wiring to the sensor, causing a short to voltage or open circuitlikely
Corroded, loose or contaminated connector at the sensor or control unitlikely
Faulty catalyst temperature sensor (internal failure)likely
Genuinely overheated catalytic converter from misfire or rich runningpossible
Fault in the sensor's reference or supply voltage, such as a short to a supply wire in the harnesspossible
Faulty engine control unit or its sensor input circuitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting any misfire, fuel trim or other catalyst-related codes
Inspect the sensor wiring along its whole run for chafing, melting, exhaust heat damage and signs of water ingress
Check the sensor and control unit connectors for corrosion, bent or pushed-back pins and poor retention
Look at live data for the catalyst temperature reading and see whether it is stuck at maximum or implausible compared with the exhaust gas temperature and engine load
With the ignition off, unplug the sensor and test the wiring for continuity, short to supply and short to earth against the manufacturer's wiring diagram
Check the sensor supply and signal voltages at the connector against the manufacturer's specification, as the sensor type and circuit layout vary by model
Check for engine faults that could genuinely overheat the catalyst, such as misfires or a rich mixture, and check the converter for signs of overheating
Measure the sensor resistance or output against specification if the manufacturer provides figures

How to fix

Repair or replace damaged wiring and secure it away from hot exhaust components
Clean or replace corroded or damaged connectors and terminals
Replace the catalyst temperature sensor if it fails electrical tests
Correct any misfire, fuelling or ignition fault that is overheating the catalyst, then check the converter condition
Repair the harness short to supply or any reference voltage fault found during testing
Replace or have the control unit repaired only if all wiring and sensor tests are good and the fault remains

Can I keep driving?

Medium severity

The car can usually be driven short-term, but get it checked soon because the fault may hide a real overheating problem and could stop catalyst monitoring. If you notice a loss of power, a burning smell or a flashing warning light, stop driving and seek help.

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