P042C code meaning
Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 2
Powertrain system Generic code P04xx codes Check engine light
What P042C means
Some engines – mainly diesels – measure the temperature at or in the catalyst with a thermistor in a voltage divider instead of only modelling it; most makers report exhaust temperature sensors under P0544 ff, P2031 ff or P2080 ff instead. Sensor 2 of bank 1 is a second, further downstream catalyst temperature sensor on the side with cylinder 1. P042C means the signal voltage is below its lower limit – typically the signal wire is shorted to ground or the sensor is shorted internally. No manufacturer document available to us uses this code; the description follows CARB, which requires input circuits to be checked for circuit faults and plausibility, and the comparable exhaust temperature sensors.
P042C at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P042C
- Check engine light on
- Usually no noticeable change (substitute value from the model)
- Diesel: filter regeneration distorted or blocked, possibly further codes such as P2459 or P0420
Common causes of P042C
- Most likelySignal wire shorted to ground (chafed)
- PossibleSensor shorted internally
- PossibleWater or corrosion in the connector
- Less likelyEngine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Catalyst temperature sensor b1s2Sensor wiringEngine control module
What each part of P042C means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 2C | The exact fault in that area. |
What to do next
- Note P042C and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P042C
What does P042C mean?
P042C means "Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 2". Some engines – mainly diesels – measure the temperature at or in the catalyst with a thermistor in a voltage divider instead of only modelling it; most makers report exhaust temperature sensors under P0544 ff, P2031 ff or P2080 ff instead. It is a generic code, so it means the same on every make.
Is it safe to drive with P042C?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P042C fail an emissions test?
Yes, it can. P042C is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P042C to fix?
Difficulty: medium. A typical repair takes 0.5 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P042C clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.