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P codepowertrainMedium severity

P046ACatalyst Temperature Sensor 1/2 Correlation (Bank 1)

The readings from the first and second catalyst temperature sensors on bank 1 do not agree with each other.

Definition

On engines with multiple exhaust temperature sensors around the catalyst or aftertreatment system, the module continuously compares the upstream (sensor 1) and downstream (sensor 2) catalyst temperature readings on bank 1, which should correlate predictably during warm-up and steady operation. P046A sets when the two readings diverge beyond a calibrated limit, indicating one sensor is skewed or the exhaust between them is behaving abnormally. On diesels this can suspend DPF regeneration and trigger derate over time; on any application it turns on the MIL and can cause an emissions-test failure.

Common causes

  • Skewed or drifting exhaust gas temperature sensor (either sensor 1 or 2)
  • EGT sensor connectors swapped after exhaust service
  • Exhaust leak between the two sensors cooling the downstream reading
  • Soot or ash coating insulating a sensor tip
  • Damaged wiring or high-resistance connection in one sensor circuit
  • Restricted or damaged catalyst/DPF altering the temperature gradient

Common misdiagnoses

  • Diesel particulate filter replacement
  • Catalytic converter replacement
  • Both temperature sensors replaced when only one is skewed
  • Diesel oxidation catalyst

Troubleshooting steps

  1. 1.Compare both sensors cold

    After an overnight soak, both catalyst temperature sensors should read within about 10 degrees F of each other and of ambient/IAT; a sensor that disagrees cold is skewed.

  2. 2.Verify sensor locations and connectors

    Confirm sensor 1 and sensor 2 connectors are not crossed, especially if the exhaust, DPF, or sensors were recently serviced.

  3. 3.Watch both readings during warm-up

    Graph both sensors from cold start; the upstream sensor should lead the downstream sensor smoothly, and a flat-lined, lagging, or erratic trace identifies the faulty sensor.

  4. 4.Inspect for exhaust leaks

    Check flanges, clamps, and welds between the two sensors for soot trails or audible leaks that would cool the downstream sensor.

  5. 5.Check sensor resistance and wiring

    Compare each sensor's resistance to the manufacturer's temperature chart and inspect harness routing near the exhaust for heat-damaged insulation.

  6. 6.Replace the skewed sensor and verify

    Install the confirmed-bad sensor, clear the code, and complete a full warm-up drive cycle to confirm correlation is restored.

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