Powertrain, generic · Auxiliary emission controls

P042A Catalyst Temperature Sensor Circuit Bank 1 Sensor 2

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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. P042A is the general circuit fault, used where the module does not separate low and high. 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.

Likely causes

Sensor faulty (element or lead broken by heat or vibration)
Harness chafed or scorched at the exhaust, connector corroded
Connector loose or pins pushed back
Engine module input

Symptoms

  • 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

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–300
Time0.5–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

catalyst temperature sensor b1s2sensor wiringengine control module

Related codes

P042BP042CP043AP0425P2031P0420

References: law.cornell.edu, hella.com, gsi.ext.gm.com.