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DTC P1900 - Radiator Cooling Fan Control

  1. Low Speed Operation

    Turn ignition off. Disconnect radiator cooling fan relay No. 2. See Fig 2. Start engine and allow to idle. Set temperature lever to full cold position. Turn A/C switch on. Turn blower fan switch on. Allow engine to idle for several minutes with A/C operating. If fan does not operate at low speed, go to next step. If fan operates at low speed, go to step 7).

  2. Check Power Supply

    Turn ignition off. Disconnect radiator cooling fan relay No. 1. See Fig 1. Turn ignition on. Measure voltage between ground and relay No. 1, terminals No. 1 and 5. See Fig 4. If battery voltage is present, go to step 4). If battery voltage is not present, go to next step.
  3. Check 10-amp fuse, 30-amp fusible link and harness connectors. Ensure continuity exists between fan relay No. 1 and battery. Repair or replace harness and/or connector as necessary.

  4. Check Ground Circuit

    Turn ignition off. Disconnect cooling fan motor harness connector. See Fig 3. Check for continuity between relay No. 1 terminal No. 3 cooling fan motor connector terminal "1". See Fig 5. Continuity should be present. Check for continuity between engine ground and cooling fan motor connector terminal "4". See Fig 6. If continuity is not present, repair harness or connectors. If continuity is present, go to next step.

  5. Check Output Signal Circuit

    Leave ignition off. Disconnect ECM harness connector. Check for continuity between fan relay No. 1 terminal No. "2", and ECM harness connector terminal No. 34. See Fig 7. If continuity is not present, repair harness or connector. If continuity is present, go to next step.

  6. Check Low Speed Cooling Fan Motor

    With cooling fan motor disconnected, apply fused battery power to terminal No. "1". Connect terminal No. 3 to ground. Refer to Fig 10. Replace cooling fan motor if it does not operate. If motor operates, Check connector pins for damage or corrosion. Check all circuit connectors for clean, tight fit and service if necessary. Loosen and retighten engine ground screws. See Figure under DTC P0100 - MASS AIRFLOW (MAF) SENSOR . If fault is still present, go to next step.

  7. Check High Speed Operation

    Turn ignition off. Disconnect radiator cooling fan relays No. 1 and 2. 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 fan operates at high speed, go to step 14). If fan does not operate at high speed, turn ignition off and go to next step.

  8. Check Power Supply

    Turn ignition on. Measure voltage between ground and relay No. 2, terminals No. 1 and No. 5. If battery voltage is present, go to next step. If battery voltage is not present, check 10-amp fuse, 30-amp fusible link and harness connectors. Ensure continuity exists between fan relay No. 2 and battery. Repair or replace harness and/or connector as necessary.

  9. Check Ground Circuit

    Turn ignition off. Disconnect cooling fan motor harness connector. Check for continuity between cooling fan connector terminal No. "2" and relay No. 2, terminal No. "3". Check for continuity between cooling fan connector terminal No. "4" and engine ground. See Fig 8. If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.

  10. Check Output Signal Circuit

    Leave ignition off, relay and cooling fan motor harness connector disconnected. Disconnect ECM harness connector. Check for continuity between relay No. 2, terminal No. "2" and ECM connector terminal No. 33. See Fig 9. If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.

  11. Check High Speed Cooling Fan Motor

    With cooling fan motor disconnected, apply fused battery power to terminal No. "2". Connect terminal No. "4" to ground. See Fig 10. Replace cooling fan motor if it does not operate. If motor operates, go to next step.

  12. Check Cooling Fan Relay

    Connect relay terminal No. "1" to ground. See Fig 11. Using jumper wire, apply battery voltage to terminal No. "2". Check continuity as follows:
    • Verify continuity is present between relay terminals No. "3" and "5".

    Remove battery voltage from relay. Check continuity as follows:

    • Verify continuity is not present between relay terminals No. "3" and "5".

    If continuity is not as specified, replace cooling fan relay. If continuity is as specified, go to next step.

  13. Disconnect ECM wiring harness connector. Check connector pins for damage or corrosion. Check all circuit connectors for clean, tight fit and service if necessary. Loosen and retighten engine ground screws. See Figure under DTC P0100 - MASS AIRFLOW (MAF) SENSOR. If fault is still present, go to next step.

  14. Check Triple-Pressure Switch Circuit

    Turn ignition off. Locate triple switch on A/C receiver/dryer. Disconnect triple switch harness connector. Check for continuity between cooling fan relay No. 1, terminal No. "2" and triple-switch connector terminal No. 4. Check for continuity between triple-switch connector terminal No. 3 and body ground. If continuity is present, replace triple switch. If continuity is not present, repair harness between triple-switch and cooling fan relay.
Fig 1: Locating Cooling Fan Relay No. 1 (Q45)
G96C10761Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: Locating Cooling Fan Relay No. 2 (Q45)
G96D10762Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 3: Locating Cooling Fan Motor Harness Connector (Q45)
G96E10763Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 4: DTC P1900, Checking Low Speed Cooling Fan Power Supply Circuit (Q45)
G96F10764Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 5: DTC P1900, Checking Low Speed Cooling Fan Ground Circuit (Q45)
G96G10765Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 6: DTC P1900, Checking Low Speed Cooling Fan Ground Circuit (Q45)
G96H10766Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 7: DTC P1900, Checking Low Speed Cooling Fan Output Signal Circuit (Q45)
G96I10767Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 8: DTC P1900, Checking High Speed Cooling Fan Ground Circuit (Q45)
G96J10768Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 9: DTC P1900, Checking High Speed Cooling Fan Output Signal Circuit (Q45)
G96A10769Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 10: DTC P1900, Checking Cooling Fan Motor (Q45)
G96D10770Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 11: DTC P1900, Checking Cooling Relay (Q45)
G96E10771Courtesy of NISSAN MOTOR CO., U.S.A.
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