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Home / DTC / P0425 — Catalyst Temperature Sensor Circuit Bank 1 Sensor 1

P0425 — Catalyst Temperature Sensor Circuit Bank 1 Sensor 1

Detailed page for trouble code P0425.

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Code

P0425

Generic P — Powertrain

Catalyst Temperature Sensor Circuit Bank 1 Sensor 1

Brand: Generic
Type: P — Powertrain
Views: UK: 20 EN: 22 RU: 39
AI status
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Page language: EN

Causes

  • Open circuit in catalyst temperature sensor wiring
  • Short to ground or battery in sensor circuit
  • Corroded or loose connector at the sensor
  • Failed catalyst temperature sensor (thermistor/heated element)
  • Exhaust leak near the sensor causing abnormal readings
  • Damage from heat or physical contact (wiring/connector)

Symptoms

  • Malfunction Indicator Lamp (MIL/CEL) illuminated
  • Freeze-frame data showing abnormal exhaust/catalyst temperature or inconsistent sensor signal
  • Possible failed emissions test or high tailpipe emissions readings
  • Occasional intermittent codes with vibration or when cold/hot
  • In rare cases, drivability issues if PCM uses temp input for diagnostics or fuel strategy

What to check

  • Retrieve freeze-frame and freeze-data with a scan tool; note engine load, RPM, and temperatures when the code set
  • Perform a visual inspection of the sensor, wiring harness, and connector for damage, corrosion, or heat exposure
  • Check for exhaust leaks near the sensor and catalytic converter flanges
  • Confirm proper connector engagement and absence of water/soot in connector
  • Use a scan tool to monitor live catalyst/exhaust temperature data and compare to expected behavior during warm-up and under load
  • Wiggle test wiring and connectors while viewing live data to reproduce intermittent faults

Signal parameters

  • Sensor type: exhaust catalyst temperature sensor (thermistor or temperature sensor style); some designs include a heater circuit
  • Typical electrical interface: signal voltage in the vehicle network range (0–5 V) or resistance change mapped to temperature by the PCM
  • Expected behavior: sensor voltage/resistance should change smoothly as exhaust temperature rises with engine load; no constant open or short readings
  • Exhaust temperature range: idle/warmup may be low (~200°C and up under increasing load; normal operating can exceed 600–800°C under heavy load) — exact temps vary by vehicle and operating conditions

Diagnostic algorithm

  1. Connect a quality OBD-II scanner. Read and record DTCs and freeze-frame data. Clear codes and attempt to re-create the fault with a monitored road or dyno test.
  2. Visually inspect Sensor 1 (pre-catalyst) and surrounding exhaust for leaks, damage, soot infiltration, or melted wiring. Repair any obvious damage.
  3. With ignition OFF, disconnect sensor connector. Inspect pins for corrosion, bent pins, or carbon tracking. Clean or repair as needed.
  4. Backprobe the sensor connector with ignition ON (engine OFF) and with engine running as appropriate. Measure reference voltage/power (if heated sensor), ground continuity, and signal voltage while warming engine. Compare to expected smooth change with temperature.
  5. If the sensor is a thermistor type, measure resistance vs temperature (cold vs hot) and confirm it changes. If the sensor has a heater, check heater supply voltage and ground and heater current where applicable.
  6. Check continuity from the sensor connector to the PCM for opens/shorts and check for short to battery or ground. Repair wiring faults found.
  7. If wiring and connectors test good but the sensor signal is erratic or out of range, replace the catalyst temperature sensor (Bank 1 Sensor 1). Clear codes and test drive to verify the fault does not return.
  8. If problem persists after sensor replacement, inspect the catalytic converter and upstream exhaust for internal damage or blockage and consider PCM diagnosis or replacement only after exhaust and wiring are confirmed good.

Likely causes

  • Failed Bank 1 Sensor 1 temperature sensor
  • Open or short in the sensor signal or power/heater wires
  • Connector corrosion or poor pin contact at sensor
  • Exhaust leak between manifold and sensor or at the catalytic converter
  • Heat-damaged wiring harness or melted insulation

Fault status

⚠️ Status
Catalyst Temperature Sensor Circuit Bank 1 Sensor 1 — circuit fault detected (open/short/intermittent).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0420 P0421 P0430 P0431 P0426
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