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P0420 – OBD-II DTC

OBD-II DTC P0420 – Secondary Air Injection System Relay “B” Circuit Malfunction

DTC P0420 meaning

DTC P0420 refers to a malfunction in the Secondary Air Injection System Relay “B” circuit. This system is designed to reduce emissions during cold starts by injecting air into the exhaust stream, helping to burn off excess hydrocarbons. When the Engine Control Module (ECM) detects a problem with the relay circuit, it triggers this diagnostic trouble code (DTC).

DTC P0420 symptoms

Common symptoms associated with DTC P0420 may include:

  • Check Engine Light (CEL) illuminated
  • Increased emissions
  • Rough engine idle
  • Decreased fuel efficiency
  • Failed emissions test

DTC P0420 causes

Several factors can lead to the triggering of DTC P0420, including:

  • Faulty Secondary Air Injection System Relay
  • Wiring issues or short circuits in the relay circuit
  • Faulty air injection pump
  • Blocked or damaged air injection hoses
  • ECM software issues

DTC P0420 seriousness

DTC P0420 is considered a moderate to serious issue. While it may not cause immediate engine damage, it can lead to:

  • Increased emissions, which can affect air quality
  • Potential failure of emissions testing
  • Reduced engine performance and fuel efficiency

How to diagnose DTC P0420

To diagnose DTC P0420, follow these steps:

  1. Use an OBD-II scanner to confirm the presence of DTC P0420.
  2. Inspect the Secondary Air Injection System Relay and its wiring for damage or corrosion.
  3. Test the relay for proper operation using a multimeter.
  4. Check the air injection pump for functionality.
  5. Examine hoses for blockages or leaks.
  6. Review ECM software for updates or faults.

How to fix DTC P0420 step-by-step instructions

To fix DTC P0420, follow these steps:

  1. Replace the faulty Secondary Air Injection System Relay if testing indicates it is defective.
  2. Repair or replace any damaged wiring or connectors in the relay circuit.
  3. Replace the air injection pump if it is not functioning properly.
  4. Clear any blockages in the air injection hoses or replace them if damaged.
  5. Reprogram or update the ECM if necessary.
  6. Perform a test drive to ensure the issue is resolved and the Check Engine Light does not reappear.

How to erase DTC P0420

To erase DTC P0420 from the vehicle’s computer, follow these steps:

  1. Connect an OBD-II scanner to the vehicle’s diagnostic port.
  2. Turn on the ignition without starting the engine.
  3. Navigate to the “Erase Codes” or “Clear DTCs” option on the scanner.
  4. Confirm the action to clear the codes.
  5. Disconnect the scanner and start the engine to verify that the Check Engine Light is off.

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