Code
P1425
FIAT
P — Powertrain
Catalytic converter 2 temperature fault
Views:
UK: 6
EN: 8
RU: 5
AI status
Completed
Completed
100%
Causes
- Faulty catalytic converter temperature sensor (open, short, drift)
- Damaged or corroded sensor connector or wiring harness (open, short to ground or Vb)
- Exhaust leak upstream of the sensor causing incorrect temperature readings
- Failed or degraded catalytic converter (insufficient exothermic reaction)
- ECU fault or intermittent software/communication error
- Sensor installed in wrong location or mounting loose/blocked
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Possible failed emissions test (increased tailpipe emissions)
- Reduced engine performance or limp-home mode in some vehicles
- Possible reduction in fuel economy
- Exhaust odor, soot, or audible exhaust leaks (if present)
What to check
- Read and record stored trouble codes and freeze frame data with a capable scan tool
- Check live data: catalytic converter temperature sensors (bank 2) and compare to bank 1 / upstream sensor behavior
- Visually inspect sensor, connector and wiring for damage, corrosion, rodent chew or heat damage
- Perform resistance/continuity check of sensor heater (if equipped) and wiring back to ECU
- Check for exhaust leaks or cracks in manifold/downpipe upstream of the sensor
- Inspect the catalytic converter for physical damage, melting, or clogging (backpressure test if suspect)
Signal parameters
- Sensor output reported as engine-control-unit calculated temperature or sensor voltage/mV/thermistor resistance depending on sensor type
- Expected behavior: sensor temperature should rise with engine load and time; downstream (post-cat) temperature should show catalyst exotherm (often higher than upstream when converter active)
- Typical expected pattern: rising temperature during warm-up and under load; sudden drops, no change, or implausible values (open/short) indicate fault
- Check for heater circuit continuity (if present) and that sensor voltage/temperature values are within manufacturer-specified ranges (consult FIAT service data)
Diagnostic algorithm
- Connect an OBD-II scanner, record codes and freeze-frame/free-running data; note operating conditions when fault set.
- With engine warm and safely secured, monitor live temps for upstream and downstream/catalyst #2 sensor while performing a controlled load (accelerate or sustained throttle). Compare relative behavior and delta temperature.
- Visually inspect the sensor and harness. Repair any obvious connector corrosion, pin damage, or insulation breaches.
- Perform resistance/continuity checks on sensor leads and heater circuit (if applicable). Repair/replace wiring as needed.
- Check for exhaust leaks upstream of the sensor (smoke test or visual). Repair leaks, then retest.
- If wiring and connectors OK but sensor readings implausible, replace the catalytic converter temperature sensor and retest.
- If sensor replacement does not clear issue, evaluate catalytic converter integrity (backpressure test, inspect for melting/clogging). Replace catalyst if degraded.
- If hardware checks out, verify ECU operation and reflash/update software if a known issue exists; consult FIAT technical service bulletins.
- After repairs, clear codes and perform full drive cycle to confirm fault does not return. Do not conclude final repair until confirmed under varying conditions.
Likely causes
- Temperature sensor failure or internal short/open
- Poor connector contact or broken wiring between sensor and ECU
- Exhaust leak or restriction affecting local temperatures
- Degraded catalytic substrate not heating as expected
Fault status
Status
Catalytic converter 2 temperature fault — temperature sensor reading out of expected range or inconsistent with other sensor inputs.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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