Diagnostic Procedure

WARNING: This page is about a different car, the 2005 Infiniti G35. However, it is still accessible from the selected car via links, so may be relevant.

CHECK GROUND CONNECTIONS
1. Turn ignition switch OFF.
2. Loosen and retighten two ground screws on the body. Refer to Ground Inspection .
  
  Fig 1: ECT Sensor Check Ground Connections (DTC P0117, P0118)
  Courtesy of NISSAN MOTOR CO., U.S.A.
OK or NG
1. OK: GO TO 2.
2. NG: Repair or replace ground connections.
CHECK ECT SENSOR POWER SUPPLY CIRCUIT
1. Disconnect engine coolant temperature (ECT) sensor harness connector.
2. Turn ignition switch ON.
  
  Fig 2: Check ECT Sensor Power Supply Circuit
  Courtesy of NISSAN MOTOR CO., U.S.A.
3. Check voltage between ECT sensor terminal 1 and ground with CONSULT-II or tester.
  1. Voltage: Approximately 5V
OK or NG
1. OK: GO TO 3.
2. NG: Repair open circuit or short to ground or short to power in harness or connectors.
Fig 3: Checking Voltage Between ECT Sensor Terminal 1 & Ground
Courtesy of NISSAN MOTOR CO., U.S.A.
CHECK ECT SENSOR GROUND CIRCUIT FOR OPEN AND SHORT
1. Turn ignition switch OFF.
2. Disconnect ECM harness connector.
3. Check harness continuity between ECT sensor terminal 2 and ECM terminal 67. Refer to Wiring Diagram.
  1. Continuity should exist.
4. Also check harness for short to ground and short to power.
OK or NG
1. OK: GO TO 4.
2. NG: Repair open circuit or short to ground or short to power in harness or connectors.
CHECK ENGINE COOLANT TEMPERATURE SENSOR
Refer to Component Inspection .

OK or NG
1. OK: GO TO 5.
2. NG: Replace engine coolant temperature sensor.
CHECK INTERMITTENT INCIDENT
Refer to TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT .
1. INSPECTION END