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DTC P1900: Radiator Cooling Fan Control

  1. Check Cooling Fan Operation  - Turn ignition off. Disconnect triple-pressure switch harness connector. See Fig 1. Disconnect Engine Coolant Temperature (ECT) sensor connector. Connect a 150-ohm resistor between ECT terminals. Start engine and allow to idle for several minutes. If cooling fan operates, go to next step. If fan does not operate, go to step 3).
  2. Check Triple-Pressure Switch Circuit  - Turn ignition off. Disconnect ECM harness connector. Check for continuity as follows: See Fig 4.
    • Between ECM connector terminal No. 36 and triple-switch connector terminal No. 4.
    • Between triple-switch connector terminal No. 3 and body ground.

    If continuity is not present, go to next step. If continuity is present, check cooling system for faults that would cause engine overheating. Check ECT sensor for correct operation. See DTC P0115: ENGINE COOLANT TEMPERATURE (ECT) SENSOR. If no faults are found, replace triple-switch.

  3. Check Power Supply  - Turn ignition off. Disconnect cooling fan relay. See Fig 2. Turn ignition on. Measure voltage between ground and relay terminals No. 2 and No. 5. See Fig 5. If battery voltage is present, go to next step. If battery voltage is not present, repair harness or connectors between cooling fan relay and ignition switch.
  4. Check Ground Circuit  - Turn ignition off. Disconnect cooling fan motor harness connector. See Fig 3. Check for continuity as follows: See Fig 6.
    • Between cooling fan motor connector terminal No. 1 and relay terminal No. 3.
    • Between cooling fan motor connector terminal No. 2 and body ground.

    If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.

  5. Check Output Signal Circuit  - Leave ignition off, relay and cooling fan motor harness connector disconnected. Disconnect ECM harness connector. Check for continuity between relay terminal No. 1 and ECM connector terminal No. 14. See Fig 7. If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.
  6. Check Cooling Fan Relay  - Connect relay terminal No. 3 to ground. Using jumper wire, apply battery voltage to terminal No. 5. Verify continuity is present between relay terminals No. 1 and 2. Remove battery voltage from relay. Verify continuity is not present between relay terminals No. 1 and 2. If continuity is not as specified, replace cooling fan relay. If continuity is as specified, go to next step.
  7. Check Cooling Fan Motor  - With cooling fan motor disconnected, apply fused battery power to terminal of White/Green wire terminal. When ground is supplied to the other terminal, cooling fan motor should operate. If motor operates, testing is complete. If cooling fan motor does not operate, go to next step.
  8. Loosen and retighten engine ground screws. See Figure. Disconnect ECM wiring harness connector. Check connector pins for damage or corrosion. Check all circuit connectors for clean, tight fit and service if necessary.
Fig 1: Locating Triple Switch Harness Connector
G96G10393Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: Locating Cooling Fan Relay
G96H10394Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 3: Locating Cooling Fan Motor Harness Connector
G96I10395Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 4: DTC P1900, Checking Triple-Pressure Switch Circuit
G96J10396Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 5: DTC P1900, Checking Power Supply Circuit
G96A10397Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 6: DTC P1900, Checking Ground Circuit
G96B10398Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 7: DTC P1900, Checking Ouput Signal Circuit
G96C10399Courtesy of NISSAN MOTOR CO., U.S.A.
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