P0419
Secondary Air Injection System Control B Circuit
If your vehicle's onboard computer has flagged the diagnostic trouble code P0419, it refers to a detected anomaly regarding "Secondary Air Injection System Control B Circuit". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
When your OBD2 scanner shows P0419, the engine control module has flagged an issue specifically related to secondary air injection system control b circuit. On the road, this usually shows up as check engine light on, failed smog inspection. No immediate danger, but addressing this soon will prevent potential emissions test failures and minor system degradation.
Symptoms
Check engine light on, failed smog inspection
Common Causes
- Failed secondary air injection pump relay B
- Faulty secondary air pump B (if equipped)
- Damaged wiring to pump B
- Corroded relay socket
How to Fix
- 1 Replace relay B
- 2 Replace secondary air pump B
- 3 Fix damaged wiring
- 4 Clean relay socket and terminals
Technical Explanation
The PCM triggers P0419 after its internal monitoring routine detects that a specific circuit or sensor has exceeded its acceptable operating range. The PCM commands the relevant emission control valve or solenoid and then verifies system response through a dedicated feedback mechanism — either a position sensor, a downstream pressure sensor, or changes in O2 sensor activity patterns. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
Low-severity fault — you'll notice check engine light on, failed smog inspection but the vehicle remains drivable. The risk of ignoring it long-term is a failed smog test and the possibility that a minor $20 fix becomes more complex over time.
Mechanic's Pro Tip
Before replacing any component on P0419, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
Relay: $20; Air pump: $150 - $400