Failed secondary air injection control module, often due to internal corrosion or water intrusion.; Corroded, loose, or damaged electrical connector at the control module or the secondary air pump.; Open or shorted wiring in the control module circuit, including chafed harnesses near the exhaust or battery box.; Blown fuse or relay supplying power to the secondary air injection control module.; Faulty secondary air pump drawing excessive current, which can damage the control module over time.; Water ingress into the control module housing or connector, common on models with the module mounted low in the engine bay.

DTC codes / Volkswagen codes / P1420

P1420 · VolkswagenSecondary Air Injection Control Module Electrical Malfunction

P1420 on Volkswagen vehicles indicates that the engine control module has detected an electrical fault in the secondary air injection control module circuit, which typically involves the control module itself or its wiring. The computer monitors the circuit for expected voltage or resistance and flags the code when the signal is out of range, often due to an open, short, or failed module.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
A brief rough idle or stumble immediately after a cold start, lasting 30 to 90 seconds.
Slight hesitation or reduced power during the first minute of driving after a cold start.
A faint hissing or rushing air sound from the engine bay during cold-start idle, if the pump runs but the module is faulty.
In rare cases, a stored pending code that reappears after clearing without any driveability change.

Common causes, most likely first

Failed secondary air injection control module, often due to internal corrosion or water intrusion.
Corroded, loose, or damaged electrical connector at the control module or the secondary air pump.
Open or shorted wiring in the control module circuit, including chafed harnesses near the exhaust or battery box.
Blown fuse or relay supplying power to the secondary air injection control module.
Faulty secondary air pump drawing excessive current, which can damage the control module over time.
Water ingress into the control module housing or connector, common on models with the module mounted low in the engine bay.

How to diagnose and fix it

Check all fuses and relays related to the secondary air injection system, including the module's power supply, and replace any blown fuse.
Inspect the control module connector and the secondary air pump connector for corrosion, water intrusion, or loose pins, and clean or repair as needed.
Perform a visual inspection of the wiring harness between the control module and the pump, looking for chafing, burns, or breaks, and repair any damaged wires.
Use a scan tool to command the secondary air pump on and off while listening for pump operation and checking for voltage at the pump connector.
Measure resistance and voltage on the control module circuit according to the factory wiring diagram to confirm an open or short.
If the circuit tests good but the code persists, substitute a known-good control module and retest before replacing parts.
After repairs, clear the code and perform a cold-start drive cycle to verify the secondary air system completes its self-test without resetting the code.

Common misdiagnosis traps for P1420

A failed secondary air pump often gets replaced when the real fault is the control module, so always test the module's output before condemning the pump.
Water intrusion into the control module connector is a frequent cause on Volkswagens with the module mounted low, and the corrosion can be hidden inside the pins.
The code can set intermittently due to a marginal connection that only fails during cold, damp weather, so a wiggle test of the harness while monitoring live data is valuable.
A blown fuse for the secondary air system may be caused by a shorted pump, so replacing the fuse without checking the pump can lead to a repeat failure.
P1420 does not always mean the module is dead; a poor ground connection at the module or chassis can produce the same electrical fault code.

Can I keep driving with P1420?

You can usually continue driving with P1420 because the secondary air system only operates during cold starts and does not affect normal engine operation, but avoid long-term neglect since a failed pump or module can lead to emissions test failure. Have the fault diagnosed soon, especially if you notice rough running after cold starts or if the check engine light flashes.

Tools that help

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Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.