LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 1998 >> RAV4 Base, 4D Utility, AWD, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Self-Diagnostic Tests >> DTC P0401: Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (Using OBD-II Scan Tool)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Check all EGR system vacuum hoses. Replace as necessary. If vacuum hoses are okay, access ECM behind bottom center of instrument panel, in front of console. Ensure ignition is off. Disconnect ECM E4 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 23 (Black/White wire) at ECM E4 connector.
  2. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Apply air pressure to VSV port "E". Air from port "E" should flow through filter on end of valve. See Figure. Disconnect jumper wire. Air from port "E" should flow from port "G". 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. Apply air pressure to VSV port "E". Air from port "E" should flow from small filter on end of valve. See Figure. Remove battery voltage from valve terminals. Air from port "E" should flow from port "G". Replace VSV as necessary.
  5. 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 wiring as necessary.
  6. Check EGR system and components. See appropriate SYSTEM/COMPONENT TESTS article. Repair as necessary. If EGR system is okay, check Manifold Absolute Pressure (MAP) sensor. See appropriate SYSTEM/COMPONENT TESTS . Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM.
scientia non olet · About LEMON Manuals