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P codepowertrainMedium severity

P2438Secondary Air Injection System Air Flow/Pressure Sensor Circuit High (Bank 2)

The Bank 2 secondary air injection air flow/pressure sensor signal is stuck above its normal operating range.

Definition

The PCM continuously checks that the Bank 2 secondary air injection pressure sensor signal stays within its expected electrical window, typically about 0.5 to 4.5 volts on a 5-volt reference. P2438 sets when the signal voltage is pegged high, indicating an open signal-return/ground, a short to voltage, or a failed sensor. The engine runs normally, but the MIL illuminates, SAI monitoring is disabled, and the vehicle will not pass an OBD emissions inspection.

Common causes

  • Failed SAI air flow/pressure sensor (often from exhaust moisture or soot intrusion)
  • Open sensor ground/return wire, forcing the signal to pull up
  • Signal wire shorted to 5 V reference or battery voltage
  • Corroded or backed-out terminal in the sensor connector
  • Damaged harness section routed near the exhaust
  • Faulty PCM input circuit (rare)

Common misdiagnoses

  • Secondary air pump replaced for a purely electrical sensor-circuit fault
  • Air switching valve replaced when the signal problem is in the wiring
  • PCM replaced before checking the ground/return circuit
  • Sensor replaced repeatedly when a harness short to voltage keeps damaging the reading

Troubleshooting steps

  1. 1.Read the sensor PID key-on engine-off

    A signal near 4.9-5 V confirms a circuit-high condition rather than a rationality fault.

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

    If the reading stays pegged high with the sensor disconnected, the fault is a wiring short to voltage or a PCM issue, not the sensor.

  3. 3.Verify the three circuits at the connector

    With key on, expect 5 V on the reference terminal, near 0 V on the ground/return (check with a test light or voltage-drop under 0.1 V), and confirm the signal wire isn't carrying voltage when disconnected from the sensor.

  4. 4.Inspect the harness near the exhaust

    Look for melted insulation or chafe points where the signal wire could contact a feed circuit.

  5. 5.Replace the sensor and retest

    If the reference and ground are good and the signal responds correctly when the sensor is unplugged, install a new sensor and confirm normal readings during a cold-start pump cycle.

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