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 P0118: Engine Coolant Temperature Sensor Circuit - High Input >> 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. Turn ignition switch to ON position. Using scan tool, observe ECT sensor values. If ECT sensor value is -40°F (-40°C), go to next step. If ECT sensor value is not -40°F (-40°C), problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO-CODES article. After repair, repeat DTC CONFIRMATION TEST .
  3. Turn ignition switch to LOCK position. Disconnect ECT sensor 2-pin harness connector C21. See Figure. Check ECT sensor and harness connector terminals for corrosion or poor connection. If connector terminals are faulty, repair as necessary and repeat DTC CONFIRMATION TEST . If connector terminals are okay, turn ignition switch to ON position and measure voltage between ground and ECT sensor harness connector C21 terminal No. 2 (Light Green wire). See Figure. If voltage is not 4-6 volts, go to next step. If voltage is 4-6 volts, go to step  6.
  4. Turn ignition switch to LOCK position. Locate ECM. See Figure. Remove ECM. See ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article. Check ECM and harness connectors for poor, loose, corroded or damaged connector terminals. If connector terminals are faulty, repair as necessary and repeat DTC CONFIRMATION TEST . If connector terminals are okay, reconnect ECM connectors and turn ignition switch to ON position. Backprobe and measure voltage between ground and ECM harness connector C46 terminal No. 12 (Light Green wire). See Figure. If voltage is not 4-6 volts, go to next step. If voltage is 4-6 volts, check for open circuit in Light Green wire between ECM and ECT sensor. If no open circuit is found, go to next step. If open circuit is found, repair as necessary and repeat DTC CONFIRMATION TEST .
  5. Turn ignition switch to LOCK position. Disconnect ECM harness connector C46. Turn ignition switch to ON position. Measure voltage between ground and ECT sensor harness connector C21 terminals No. 1 (Orange wire) and No. 2 (Light Green wire). See Figure. If voltage is zero volt, go to next step. If any voltage is found, check Light Green or Orange wire for short to other circuits between ECM and ECT sensor. If short circuit 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 .
  6. Turn ignition switch to LOCK position. Measure resistance between ECM harness connector C46 terminal No. 12 (Light Green wire) and ECT sensor harness connector C21 terminal No. 2 (Light Green wire). See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair short in Light Green wire between ECM and ECT sensor. After repair, repeat DTC CONFIRMATION TEST .
  7. Reconnect ECM harness connector and ensure proper terminal connection. Measure resistance between ground and ECT sensor harness connector C21 terminal No. 1 (Orange wire). See Figure. If resistance is 10 ohms or more, go to next step. If resistance is less than 10 ohms, go to step  9.
  8. Backprobe and measure resistance between ground and ECM harness connector C46 terminal No. 27 (Orange wire). See Figure. If resistance is less than 5 ohms, repair open or short circuit in Orange wire between ECM and ECT sensor. After repair, repeat DTC CONFIRMATION TEST . If resistance is 5 ohms or more, check ECM ground circuit (Orange wire) between ECM and ECT sensor. If ground circuit is faulty, repair as necessary and repeat DTC CONFIRMATION TEST . If ground circuit is okay, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST .
  9. Turn ignition switch to LOCK position. Perform ECT sensor component test. See ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If ECT sensor is faulty, replace ECT sensor. See ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION article. After repair, repeat DTC CONFIRMATION TEST . If ECT sensor is okay, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST .
scientia non olet · About LEMON Manuals