WOMS
P code powertrain Medium severity

P0691 Auxiliary Emission Control Circuit Range/Performance Problem

The OBD2 code P0691 indicates a problem with the auxiliary emission control circuit, specifically that its performance is outside the expected range

Definition

The OBD2 code P0691 indicates a problem with the auxiliary emission control circuit, specifically that its performance is outside the expected range

Common causes

  • Faulty auxiliary emission control module
  • Wiring issues (shorts, opens, or corrosion)
  • Poor connections or damaged connectors
  • Malfunctioning sensors related to the auxiliary emission control system
  • Failed or malfunctioning emission control components (e.g., EGR valve, catalytic converter)
  • Software issues or programming errors in the engine control module (ECM)
  • Grounding issues in the circuit

Common misdiagnoses

  • Faulty Engine Control Module (ECM)
  • Wiring issues or shorts in the circuit
  • Defective sensors (e.g., temperature or pressure sensors)
  • Malfunctioning auxiliary emission control devices
  • Incorrectly installed or damaged connectors
  • Software issues or outdated firmware in the ECM
  • Vacuum leaks affecting sensor readings
  • Faulty relays or fuses related to the emission control system

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. Sometimes, multiple codes can provide more context for the issue

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors associated with the auxiliary emission control system. Look for signs of damage, corrosion, or loose connections that could affect the circuit's performance

  3. 3. Check the Auxiliary Emission Control Components

    Identify the specific components related to the auxiliary emission control system (such as the EGR valve, EVAP system components, etc.) and check their functionality. Ensure they are operating correctly and are not clogged or damaged

  4. 4. Test the Circuit

    Use a multimeter to test the voltage and ground at the relevant connectors. Compare the readings to the specifications in the vehicle's service manual. Look for any open circuits, shorts, or abnormal resistance

  5. 5. Inspect the PCM (Powertrain Control Module)

    In some cases, the issue may be related to the PCM itself. Check for any software updates or recalls that may apply to your vehicle. If necessary, consider reprogramming or replacing the PCM

  6. 6. Check for Vacuum Leaks

    If the auxiliary emission control system relies on vacuum, inspect for any vacuum leaks that could affect performance. Use a smoke machine or carburetor cleaner to help identify leaks

  7. 7. Perform a Visual Inspection of the Exhaust System

    Ensure that there are no blockages or leaks in the exhaust system that could affect emissions readings

  8. 8. Clear the Codes and Test Drive

    After performing the necessary repairs or inspections, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  9. 9. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to your vehicle's make and model that may provide additional guidance on addressing the P0691 code

  10. 10. Seek Professional Help

    If you are unable to resolve the issue after performing these steps, it may be best to consult a professional mechanic or technician who has experience with your specific vehicle. By following these steps, you can systematically diagnose and address the underlying issue causing the P0691 code