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P codepowertrainMedium severity

P0548Exhaust Gas Temperature Sensor Circuit Low (Bank 2, Sensor 1)

The exhaust gas temperature sensor 1 circuit on Bank 2 is reading abnormally low voltage, typically from a short to ground or a shorted sensor.

Definition

The PCM supplies a reference voltage to the Bank 2, Sensor 1 exhaust gas temperature sensor and watches the returned signal. P0548 sets when the signal voltage drops below the plausible threshold, which with an NTC thermistor corresponds to an impossibly hot exhaust reading, usually caused by a short to ground in the harness or a shorted sensor element. The MIL illuminates and the PCM may take protective action such as limiting boost, altering fueling, or inhibiting DPF regeneration on diesels because it believes the exhaust is overheating, resulting in noticeable power loss.

Common causes

  • EGT sensor signal wire shorted to ground (chafed against exhaust or bracket)
  • Internally shorted EGT sensor element
  • Connector damage allowing terminals to bridge or contact ground
  • Moisture or coolant intrusion in the connector
  • Harness pinched during prior exhaust or turbo service
  • Faulty PCM input circuit (rare)

Common misdiagnoses

  • Turbocharger replaced for a perceived overheating/overboost condition
  • Catalytic converter or DPF replaced for false high-temperature readings
  • Sensor replaced repeatedly when the harness short is the true fault
  • EGR cooler suspected for high exhaust temperature indications

Troubleshooting steps

  1. 1.Check the live EGT reading key-on engine-off

    A cold engine showing an extremely high Bank 2 EGT (near maximum scale) indicates a low-voltage/short condition rather than a real temperature.

  2. 2.Unplug the sensor and re-check the PID

    If the reading snaps to the opposite extreme (open-circuit value) the wiring to the PCM is likely intact and the sensor is shorted; if it stays pegged hot, the harness is shorted to ground.

  3. 3.Measure sensor resistance

    Compare measured resistance to the temperature/resistance chart; a near-zero reading confirms a shorted element.

  4. 4.Inspect the harness for chafe points

    Trace the Bank 2 sensor wiring looking for insulation worn through against the exhaust manifold, heat shield, or brackets.

  5. 5.Repair and verify

    After repairing the short or replacing the sensor, clear the code and confirm plausible EGT readings across a full warm-up drive cycle.

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