LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 1996 >> Tercel Base, Standard >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Circuit Tests >> DTC P0401 - Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (Using OBD-II Scan Tester)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair (Using OBD-II Scan Tester)

  1. Inspect all EGR system vacuum hoses. Replace as necessary. Access ECM behind glove box. Ensure ignition is off. Disconnect ECM E6 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 15 (Black/White wire) at ECM E6 connector.
  2. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Air from port "E" should exhaust from port "F". See Figure. Disconnect jumper wire. Air from port "E" should not exhaust from port "F". If valve operates as specified, go to step 6). If valve does not operate as specified, go to next step.
  3. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68°F (20°C). Check for continuity between each terminal and body of valve. If continuity exists, replace VSV. If continuity does not exist, go to next step.
  4. Check VSV operation. Apply battery voltage to valve terminals. Air from port "E" should exhaust from port "F". See Figure. Remove battery voltage from valve terminals. Air from port "E" should not exhaust from port "F". Replace VSV as necessary.
  5. If VSV operates as specified, check for an open or short in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  6. Inspect EGR vacuum modulator. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR valve is okay, go to next step.
  7. Check Manifold Absolute Pressure (MAP) sensor. See SYSTEM/COMPONENT TESTS article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.
scientia non olet · About LEMON Manuals