LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Suzuki >> 2003 >> Aerio SX, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0401 Or DTC P0402 >> Diagnosis & Repair Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair Procedure

NOTE: For better performance and results of this diagnostic procedure, usage of appropriate wiring diagram is recommended. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
NOTE: Perform all voltage and resistance tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use an ohmmeter to isolate wiring harness shorts or opens.
  1. If engine system check has been performed, go to next step. If engine system check has not been performed, perform TEST D: ENGINE SYSTEM CHECK  under SYSTEM TESTS, then go to next step.
  2. If SUZUKI scan tool or equivalent is available, go to next step. If SUZUKI scan tool or equivalent is not available, go to step  5.
  3. Turn ignition switch to ON position. Using scan tool, check EGR system. See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. If EGR system is operating properly, go to next step. If EGR system is not operating properly, go to step  5.
  4. Turn ignition switch to LOCK position. Perform MAP sensor component test. See MANIFOLD ABSOLUTE PRESSURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If MAP sensor is faulty, repair or replace as necessary. After repair, repeat DTC CONFIRMATION TEST . If MAP sensor is okay, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO-CODES article. If no intermittent problem is found, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST .
  5. Turn ignition switch to LOCK position. Disconnect EGR valve 6-pin harness connector C44. See Figure. Turn ignition switch to ON position. Measure voltage between ground and EGR valve harness connector C44 terminals No. 2 and 5 (Black/Red wire). See Fig 1. If voltage is 10-14 volts, go to next step. If voltage is not 10-14 volts, repair open circuit in Black/Red wire between EGR valve and ECM. After repair, repeat DTC CONFIRMATION TEST .
  6. Turn ignition switch to LOCK position. Disconnect ECM harness connector C46. See Figure. Turn ignition switch to ON position. Measure voltage between ground and EGR valve harness connector C44 terminals No. 1 (Gray/White wire), No. 3 (Gray wire), No. 4 (Gray/Yellow wire) and No. 6 (Brown/White wire). See Fig 1. If all voltages are zero volt, go to next step. If any voltage is found, check for short circuit between wires between EGR valve and ECM. If short between wires is found, repair as necessary and repeat DTC CONFIRMATION TEST . If short circuit is not found, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST .
  7. Turn ignition switch to LOCK position. Measure resistance between ground and EGR valve harness connector C44 terminals No. 1 (Gray/White wire), No. 3 (Gray wire), No. 4 (Gray/Yellow wire) and No. 6 (Brown/White wire). See Fig 1. If all resistances are infinity, go to next step. If any resistance is found, check for short to ground in appropriate wire between EGR valve and ECM. If short to ground is found, repair as necessary and repeat DTC CONFIRMATION TEST . If no short to ground is found, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST .
  8. Ensure ignition switch is on LOCK position. Reconnect EGR valve harness connector and disconnect ECM harness connectors C46 and G04. See Figure. Measure resistance between ECM specified harness connectors and terminals. See CHECKING EGR VALVE SYSTEM CIRCUIT RESISTANCE  table. See Figure. Resistance should be 20-24 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, repair short or open circuit in appropriate wire. After repair, repeat DTC CONFIRMATION TEST .
    CHECKING EGR VALVE SYSTEM CIRCUIT RESISTANCE

    Measure Between ECM Harness Connector/Terminal (Wire Color) Measure Between ECM Harness Connector/Terminal (Wire Color)
    G04/8 Or 23 (Red/Black) C46/3 (Gray)
    G04/8 Or 23 (Red/Black) C46/13 (Gray/White)
    G04/8 Or 23 (Red/Black) C46/14 (Brown/White)
    G04/8 Or 23 (Red/Black) C46/15 (Gray/Yellow)
  9. Turn ignition switch to ON position. Measure voltage between ground and ECM harness connector C46 terminals No. 3 (Gray wire), No. 13 (Gray/White wire), No. 14 (Brown/White wire) and No. 15 (Gray/Yellow). See Figure. If voltage is 10-14 volts, go to next step. If voltage is not 10-14 volts, check appropriate wire for open circuit. If open circuit is found, repair as necessary and repeat DTC CONFIRMATION TEST . If no open circuit is found, replace EGR valve. See EGR VALVE under FUEL SYSTEM in REMOVAL & INSTALLATION article. After repair, repeat DTC CONFIRMATION TEST .
  10. Turn ignition switch to LOCK position. Perform MAP sensor component test. See MANIFOLD ABSOLUTE PRESSURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If MAP sensor is okay, Check for EGR passage clogged or EGR valve malfunction. If problem is found, repair as necessary and repeat DTC CONFIRMATION TEST . If no problem is found, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO-CODES article. If MAP sensor is faulty, replace MAP sensor. See MANIFOLD ABSOLUTE PRESSURE SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION article. After repair, repeat DTC CONFIRMATION TEST .
Fig 1: Identifying EGR Valve Harness Connector C44 Terminals
G00163649Courtesy of SUZUKI OF AMERICA CORP.
scientia non olet · About LEMON Manuals