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P codepowertrainMedium severity

P0428Catalyst Temperature Sensor High Input (Bank 1)

The signal from the Bank 1 catalyst temperature sensor has risen above its normal operating voltage range.

Definition

P0428 sets when the PCM sees the Bank 1 catalyst temperature sensor signal above the maximum plausible threshold, which most often means an open circuit — the internal pull-up voltage drives an open signal wire high — or a short to voltage. The PCM ignores the reading and suspends catalyst temperature monitoring and any over-temperature protection that relies on it. Expect a MIL with no driveability change; on diesels the fault can inhibit or mistime particulate filter regeneration.

Common causes

  • Open catalyst temperature sensor element (common failure mode with heat cycling)
  • Broken signal or ground wire, often at the heat-stressed section near the exhaust
  • Unplugged, corroded, or backed-out connector terminal
  • Signal wire shorted to a voltage supply
  • ECM input circuit fault (rare)

Common misdiagnoses

  • Catalytic converter replaced for a circuit-high electrical fault
  • Sensor replaced when a broken harness wire or connector is the cause
  • Oxygen sensors replaced because of the code's catalyst-range number

Troubleshooting steps

  1. 1.Confirm the pegged reading

    On a fully warmed engine the catalyst temperature PID stuck at its default or maximum value indicates an electrical fault, not a real exhaust condition.

  2. 2.Jumper the sensor connector terminals

    With the sensor unplugged, bridge the harness terminals and watch the PID; if it swings to the opposite extreme, the harness and ECM are good and the sensor is open.

  3. 3.Check circuit continuity

    Measure end-to-end resistance of the signal and ground wires between the sensor connector and the ECM; anything over a few ohms indicates a wiring break or bad terminal.

  4. 4.Inspect the connector and heat-exposed wiring

    Look for terminals pushed out of the connector body and insulation that has gone brittle from exhaust heat.

  5. 5.Measure sensor resistance

    An out-of-range or open (OL) reading across the sensor element at room temperature confirms internal failure.

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