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P0419Secondary Air Injection System Relay "B" Circuit Malfunction

There is an electrical fault in the control circuit for the second secondary-air-injection relay (Relay B).

Definition

Some secondary air injection systems use a second relay — Relay "B" — to power a second air pump or a separate bank's air delivery components, and the PCM monitors its control circuit just as it does Relay A. P0419 sets when the Relay B control circuit is open, shorted, or does not respond as commanded, commonly from a failed relay coil, corroded socket, wiring damage, or an overloaded circuit caused by a failing pump. Driveability is unaffected, but the MIL illuminates, the affected air path stops working during cold starts, emissions rise, and the vehicle will fail an emissions inspection.

Common causes

  • Failed Relay B (open coil or burned contacts)
  • Corroded relay socket or fuse box terminals
  • Open or shorted control wire between the PCM and relay
  • Seized or water-damaged air pump overloading the relay circuit
  • Blown fuse on the relay load side
  • Faulty PCM driver (rare)

Common misdiagnoses

  • Relay A replaced instead of Relay B
  • Air pump replaced when the relay socket terminal was corroded
  • PCM replaced for a wiring fault in the control circuit
  • Switching valves replaced for a relay-circuit code

Troubleshooting steps

  1. 1.Identify Relay B in the fuse box

    Use the service information to locate the correct relay, since systems with two AIR relays are easily confused and the wrong relay is often tested.

  2. 2.Bench-test or substitute the relay

    Verify the coil measures in the typical 50-120 ohm range and the contacts close, or swap in an identical known-good relay and command the AIR system on.

  3. 3.Test the control circuit from the PCM

    With the relay removed, confirm the PCM toggles the control terminal (ground or voltage per the diagram) during a bidirectional AIR test.

  4. 4.Inspect socket and load-side wiring

    Check for melted, loose, or corroded socket terminals and verify the load-side fuse and wiring to the pump are intact.

  5. 5.Measure the pump's current draw

    Energize the circuit and confirm pump current is within spec; excessive draw from a seized or waterlogged pump will keep damaging relays.

  6. 6.Confirm the monitor passes

    After repair, run a cold-start cycle and verify the secondary air monitor completes without resetting the code.

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