P0419: Secondary Air Injection System Control B Circuit

What it means

A general electrical fault on AIR system control circuit B (typically the AIR pump driver line on the second pump or relay).

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The AIR control B circuit operates a secondary-air system control path, such as a relay or pump driver, depending on the vehicle. The control module monitors that circuit during the cold-start emissions routine. P0419 sets when it detects an electrical fault on control B, so the intended AIR component may not operate.

Common causes

Most likely first.

1. AIR system control circuit B relay or driver fault
2. Open or shorted wiring
3. Loose, damaged, or corroded connector
4. Secondary air pump fault

Symptoms

• Check engine light on
• Failed emissions inspection
• Possible roughness during cold start

How to diagnose it

1. Review freeze-frame data and related AIR codes to determine when control B faulted and whether the pump or another AIR circuit was also affected.
2. Use the vehicle wiring diagram to identify the control B relay, driver, and connected pump, since the circuit arrangement varies by vehicle.
3. Inspect the control B connector, relay socket, and harness for corrosion, loose terminals, chafing, or heat damage.
4. Test the control B circuit for opens or shorts and verify relay operation and power delivery to the connected AIR component.
5. If the wiring and relay pass, check the pump or other controlled component, then verify the control module output.

Common fixes

• Clean and secure a loose or corroded control B connector.
• Repair damaged or chafed wiring in the control B circuit.
• Replace a failed control B relay or driver component identified by testing.
• Repair or replace the secondary air pump if it fails its power and operation checks.
• Repair the control module driver only after checking the connected components and circuit.

Can I keep driving?

Normal driving is often possible, but the AIR component controlled by circuit B may not operate during cold starts, increasing emissions and risking an inspection failure. If cold-start roughness or electrical symptoms occur, avoid unnecessary trips and have the circuit checked promptly.