Powertrain, generic · Auxiliary emission controls
P0425 Catalyst Temperature Sensor Circuit Bank 1 Sensor 1
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 1 of bank 1 is the first catalyst temperature sensor on the side with cylinder 1. P0425 is the general circuit fault, used where the module does not separate low and high. FCA's 3.0-litre EcoDiesel uses this sensor (middle of the oxidation catalyst and particulate filter unit), but no document available to us names this particular code.
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 b1s1sensor wiringengine control module
Related codes
References: law.cornell.edu, static.nhtsa.gov, hella.com.