What it means
A general electrical fault on the catalyst temperature sensor at bank 1 sensor 2.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The bank 1 sensor 2 catalyst temperature sensor measures temperature at the downstream sensor position on bank 1. The control module checks its electrical signal for a general circuit fault; P042A indicates the signal is faulty without specifying whether it is low, high, open, or shorted.
Common causes
Most likely first.
- Catalyst temperature sensor failure
- Open or short in the sensor wiring
- Corroded or loose sensor connector
- Fault in the control module
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Read freeze-frame data and live data for bank 1 sensor 2, and note whether its value is missing, fixed, or implausible alongside related circuit codes.
- Inspect the bank 1 sensor 2 connector and nearby harness for corrosion, loose or pushed-back pins, heat damage, and exhaust contact.
- Check the wiring for open circuits and shorts using the manufacturer's wiring diagram and specification.
- Test the sensor's electrical response and compare it with the manufacturer's specification before replacing it.
- If the sensor and harness pass, check the control-module connector and circuit driver for a fault.
Common fixes
- Reconnect the bank 1 sensor 2 plug and correct a loose terminal.
- Repair damaged, open, or shorted wiring to the sensor.
- Replace a corroded connector or damaged harness section.
- Replace the bank 1 sensor 2 temperature sensor if it fails specification.
- Repair the control module only after the sensor and circuit have tested good.
Can I keep driving?
If the vehicle runs normally, limited driving is generally possible, but avoid heavy loads if you notice a sulfur smell or a change in performance. Emissions monitoring may be impaired and the vehicle may fail inspection.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.