P0419

Secondary Air Injection System Relay B Circuit Malfunction

P0419 is a generic OBD-II powertrain diagnostic trouble code: Secondary Air Injection System Relay B Circuit Malfunction. It is logged by the engine control unit when the egr monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0419
Group
Powertrain
System
EGR
Severity
Warning (MIL on)
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What P0419 means

P0419 — "Secondary Air Injection System Control \"B\" Circuit Malfunction" — is stored when the PCM detects an electrical fault in the control circuit for the Secondary Air Injection System (SAIS) relay or control driver designated as bank \"B.\" Where P0417 specifically identifies a short in the switching valve circuit, P0419 is a broader malfunction code covering any electrical irregularity — open circuit, short, or control-signal failure — in the circuit that drives the bank B air pump relay or primary pump control solenoid.

The SAIS pumps ambient air into the exhaust manifold during cold engine start-up to reduce HC and CO emissions. The bank B circuit controls air injection on the second bank (B-side cylinders). The PCM monitors the circuit by commanding the relay on and verifying expected current flow; if the measured response deviates from the commanded state, P0419 is set. A common real-world trigger is condensation from the exhaust backflowing through the check valve into the pump, which freezes in cold weather and seizes the pump rotor — the resulting locked-rotor current spike blows the relay fuse or destroys the pump winding, causing an open-circuit malfunction.

P0419 will not impair normal driving on a warmed engine, but the vehicle will not meet OBD-II readiness requirements for the SAIS monitor, failing an emissions inspection. Repeated cold-start stalling or rough idle may occur if the air injection circuit is heavily involved in the PCM's cold-start idle strategy. Diagnosis should include inspection of the pump for water ingestion, check valve condition, and the wiring and relay serving the bank B circuit.

Common causes

Most-frequently reported root causes when P0419 is logged.

  • 1
    Failed secondary air injection pump on bank B — seized rotor due to frozen condensation (common in cold climates) or worn motor brushes.
  • 2
    Blown fuse in the bank \"B\" pump relay power supply circuit, typically caused by a pump seizure overcurrent event.
  • 3
    Faulty bank \"B\" relay — coil open or contact failure preventing power delivery to the pump or solenoid.
  • 4
    Malfunctioning one-way check valve allowing exhaust condensation to backflow into the pump housing.
  • 5
    Open circuit in the bank \"B\" control wiring due to heat damage, chafing, or broken wire near the exhaust manifold.
  • 6
    Corroded or damaged electrical connectors at the pump relay, solenoid, or PCM harness.
  • 7
    PCM output driver fault on the bank \"B\" relay control channel (rule out external components first).

Symptoms drivers notice

Malfunction Indicator Lamp (MIL / Check Engine Light) illuminates.
Engine stalling or rough idle immediately after a cold start.
Hesitation during acceleration from cold.
Unusual noises from the SAIS pump area at start-up — grinding, absence of normal pump hum, or no activation at all.
Vehicle fails OBD-II SAIS monitor readiness check, resulting in emissions test failure.
In cold climates, hard starting or extended warm-up time if the SAIS is integrated into the cold-start idle strategy.

How to diagnose P0419

A typical diagnostic flow when this code is present.

  1. 1
    Connect an OBD-II scan tool and retrieve all stored and pending codes; note companion codes such as P0417 (switching valve B shorted) or P0418 (relay A) to determine whether the fault is bank-specific or systemic.
  2. 2
    Inspect the bank \"B\" relay and its fuse — replace the fuse if blown and inspect the relay coil resistance and contact operation.
  3. 3
    Inspect the secondary air injection pump for evidence of water ingestion: remove the pump inlet hose and look for rust, moisture, or a seized rotor that does not spin freely.
  4. 4
    Test the one-way check valve for bank B — it should allow flow in one direction only; a valve that passes flow in both directions allows exhaust condensation to reach the pump.
  5. 5
    Inspect the bank \"B\" wiring harness and connectors for corrosion, broken wires, or heat damage near exhaust components.
  6. 6
    With the relay connector unplugged, verify PCM control signal switching during cold start using a test light on the relay coil control terminal.
  7. 7
    If relay, fuse, pump, and wiring are confirmed serviceable, test the PCM output before condemning the module.

Related powertrain codes

Frequently asked questions

Why does the check valve failure cause the pump to fail?

The check valve is designed to prevent exhaust gases and condensation from travelling backwards into the pump when it is not running. If the valve fails, exhaust moisture accumulates in the pump housing. In cold weather this moisture freezes around the pump rotor, seizing it when the PCM commands it on and burning out the motor windings or blowing the fuse.

What is the difference between P0419 and P0417?

P0417 specifically identifies a short circuit in the bank B switching valve circuit. P0419 is a broader malfunction code covering any fault — open circuit, short, relay failure, or pump control fault — in the bank B relay/control circuit. P0419 is often triggered by pump or relay failures, while P0417 more commonly points to wiring or solenoid shorts.

Can P0419 be triggered only in winter?

Intermittent P0419 faults that appear only in winter and self-resolve as temperatures rise are a strong indicator of condensation freezing in the pump. The pump seizes at start-up, triggering the code, then thaws as the engine warms, clearing the symptom until the next cold morning. Replace the check valve and inspect the pump for corrosion damage before the next cold season.

Is it safe to drive with P0419?

Yes, for normal driving once the engine is warm — the SAIS operates only during cold start and does not affect warm-engine performance. However, repeated pump seizure events will eventually damage the relay and wiring. Repair before the onset of cold weather to avoid a worsening fault.

Disabling P0419 in software

RaceTune can permanently disable P0419 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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