The P1420 diagnostic trouble code is a manufacturer-specific powertrain code. Its exact definition depends heavily on the vehicle make, pointing to a secondary air injection valve electrical fault or an evaporative emission system small leak.
Because this code targets entirely different systems across manufacturers, the exact vehicle application must be verified before diagnosis. The code alone does not prove a specific component has failed without proper testing.
Quick Navigation
Key Takeaways
- P1420 is a manufacturer-specific powertrain code with differing definitions depending on the vehicle make.
- On BMW, Volkswagen, and Audi applications, it indicates a secondary air injection valve circuit electrical malfunction.
- On Toyota and Lexus applications, it points to an evaporative canister small leak or EVAP system leak.
- Diagnosis requires verifying the exact factory definition and testing the relevant air valve circuit or EVAP system.
- Repairs depend on the confirmed root cause and may involve replacing a valve, fixing wiring, or sealing an EVAP leak.
P1420 Code Description and Implications
The P1420 code indicates that a control module has detected a specific fault within an auxiliary emissions or evaporative system. Because it is a manufacturer-specific code, the exact monitored component varies significantly by brand.
Some BMW, Volkswagen, and Audi applications: P1420 indicates a Secondary Air Injection Valve Circuit Electrical Malfunction. The ECU detects an open, short, or abnormal resistance in the control circuit for the secondary air valve.
Certain Toyota and Lexus applications: The code indicates an Evaporative Canister Small Leak or EVAP System Small Leak. The ECU detects a minor pressure drop in the evaporative emissions system, indicating a vapor leak.
Some Ford applications: P1420 may indicate an EVAP System Small Leak or a Secondary Air Injection System fault, depending on the exact model and year.
Common Causes of the P1420 Code
Because P1420 applies to different systems across different brands, the root cause depends on the verified vehicle application.
- Secondary Air Causes (BMW/VW/Audi): A failed secondary air injection valve, damaged wiring harness, poor electrical connections at the valve or ECU, or a failed relay.
- EVAP Causes (Toyota/Lexus/Ford): A loose or faulty gas cap, cracked vapor hoses, a failing purge valve, or a leaking charcoal canister.
Symptoms Associated With P1420
When the control module detects a critical emissions fault, it illuminates the warning light.
- Secondary Air Symptoms: The Check Engine Light will illuminate. Drivability is typically unaffected, but the vehicle may fail an emissions test due to increased cold-start pollutants.
- EVAP Symptoms: The Check Engine Light will illuminate. A faint fuel odor may be present near the vehicle, but engine performance remains normal.
Diagnosing the P1420 Trouble Code
Accurate diagnosis begins by verifying the exact vehicle application and reviewing manufacturer-specific service information.
- For BMW, VW, and Audi applications: Inspect the secondary air valve wiring harness for opens or shorts. Measure the valve’s electrical resistance and verify the control signal from the ECU.
- For Toyota, Lexus, and Ford applications: Verify the gas cap is properly sealed. Inspect all EVAP hoses for cracks or disconnections. Perform a smoke test to locate the exact source of the small leak.
Repairing the P1420 Issue
Repairs must follow the confirmed root cause identified during diagnosis.
- Secondary Air Repairs: Repair any damaged wiring in the valve circuit. If the valve fails electrical testing, replace the secondary air injection valve.
- EVAP Repairs: Tighten or replace the gas cap if it fails to seal. Replace cracked hoses, a faulty purge valve, or a leaking charcoal canister to restore system integrity.
Cost Considerations for P1420 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing a gas cap or secondary air valve involves minimal to moderate labor. However, tracking down an intermittent EVAP leak using a smoke machine or replacing a charcoal canister requires additional diagnostic and labor time.
Prevention Strategies for Future Occurrences
Ensuring the gas cap is tightened properly after every refueling helps prevent evaporative emission leaks on Toyota, Lexus, and Ford applications.
Inspecting exposed EVAP hoses and secondary air wiring for signs of heat damage or chafing during routine service can help identify developing issues before they trigger a fault code.
Troubleshooting Tips and Best Practices
Follow these practices to avoid misdiagnosis and ensure accurate repairs.
- Do not assume the catalytic converter is failing: The definition of a NOx catalyst fault is incorrect for P1420. Always verify the exact definition for your specific make.
- Check for related codes: Look for accompanying EVAP codes like P0442 or P0455 on Toyota applications, or secondary air pump codes on BMW applications.
- Verify your definition: When researching this trouble code, always confirm whether your vehicle uses the secondary air or EVAP definition.
More OBD-II Codes
| P1405 | P1406 | P1407 | P1415 |
| P1416 | P1418 | P1421 | P1423 |
| P1431 | P1433 | P1441 | P1444 |
| P0440 | P0442 | P0455 | P0456 |
| P0411 | P0420 | P0430 | P0171 |
| P0174 | P0300 | P0100 | P0016 |
Frequently Asked Questions
Is P1420 a generic or manufacturer-specific code?
No. P1420 is a manufacturer-specific powertrain code. Its definition varies significantly by brand, indicating a secondary air valve fault or an EVAP system small leak.
Can I drive my vehicle with a P1420 code?
Yes, the vehicle remains drivable. Neither a secondary air valve electrical fault nor a small EVAP leak typically affects engine performance or immediate drivability.
Will disconnecting the battery clear the P1420 code?
Disconnecting the battery might temporarily clear the code. However, it does not repair the underlying electrical fault or seal the evaporative leak, and the code will return.
Can a loose gas cap cause a P1420 code?
Yes. On Toyota, Lexus, and some Ford applications where P1420 indicates an EVAP small leak, a loose or faulty gas cap is a frequent cause of the vapor leak.
Does P1420 affect the transmission?
No. The P1420 code relates strictly to auxiliary emissions control or the evaporative emissions system. It does not directly affect the operation of the automatic or manual transmission.
What Should You Do About the P1420 Code?
When a P1420 code appears, confirm the exact factory definition for your specific vehicle make and model. Because this code targets entirely different emissions systems depending on the manufacturer, applying the wrong diagnostic path will lead to misdiagnosis.
Follow the applicable manufacturer diagnostic procedure to test the relevant system and components. Once the root cause is confirmed, complete the necessary electrical repairs or EVAP leak corrections before returning the vehicle to normal service.
