DTC P1900 - COOLING FAN CIRCUIT Nissan Maxima A32

1. Check Low Speed Fan Operation Turn ignition off. Disconnect cooling fan relays No. 2 and 3. (Scheme 34) Start engine. Turn A/C switch and blower fan switch to ON position. Allow engine to idle for several minutes. Verify cooling fan operates at low speed. If fan does not operate at low speed, go to step 4). If fan operates at low speed, go to next step.
2. Check High Speed Fan Operation Turn ignition off. Reconnect cooling fan relays No. 2 and 3. Disconnect cooling fan relay No. 1. (Scheme 34) Turn A/C switch and blower fan switch to OFF position. Disconnect Engine Coolant Temperature (ECT) sensor harness connector. see scheme 5 Connect 150-ohm resistor across ECT sensor harness connector terminals. Restart engine. Verify cooling fan operates at higher than low speed. If cooling fan does not operate as specified, go to step 7). If cooling fan operates as specified, go to next step.
3. Check Ground Circuit Turn ignition off. Disconnect cooling fan relay No. 2 and 3 harness connectors. Disconnect triple switch harness connector. Using an ohmmeter, check continuity between both cooling fan relay connector terminals No. 2 (Green wire) and triple switch harness connector terminal No. 3 (Green wire). Also, check continuity between ground and triple switch harness connector terminal No. 3 (Black wire). If no continuity exists, repair fault in circuit and retest system. If continuity exists, replace triple switch and retest system.
4. Check Power Supply (Low Speed) Turn ignition off. Disconnect cooling fan relay No. 1 harness connectors. Turn ignition on. Using a voltmeter, measure voltage between ground and cooling fan relay No. 1 harness connector, terminal No. 1 (Green/Yellow wire). Also measure voltage between ground and cooling fan relay No. 1 harness connector, terminal No. 3 (White/Blue wire). If battery voltage does not exist, repair open in White wire. If battery voltage does not exist, check for fault in circuit, blown fuse No. 17 (10-Amp) or burnt 30 Amp fusible link. If battery voltage exists, go to next step.
5. Check Ground Circuits (High Speed) Turn ignition off. Disconnect cooling fan motor No. 1 and 2 harness connectors. (Scheme 35) Using an ohmmeter, check continuity as follows: Between cooling fan relay No. 1 harness connector, terminal No. 5 (White/Black wire) and cooling fan motor No. 1 harness connector terminal 1 (White/Black wire). Between cooling fan relay No. 1 harness connector, terminal No. 5 (White/Black wire) and cooling fan motor No. 2 harness connector terminal 1 (White/Black wire). Between ground and cooling fan motor No. 2 harness connector terminal No. 4 (Black wire). If continuity is present at each circuit check, go to next step. If continuity is not present at any circuit check, repair fault in circuit and retest system.
6. Check Output Signal Circuit (Low Speed) Disconnect ECM harness connector. Using an ohmmeter, check continuity between ECM harness connector terminal No. 14 and cooling fan relay No. 1 harness connector, terminal No. 2 (Light Green/Red wire). If no continuity exists, repair fault in Light Green/Red wire. If continuity exists, check wiring harness and connectors for damage or corrosion and repair if necessary. If no faults are found, replace cooling fan relay No. 1 and retest system. If fault is still present, replace cooling fan motor.
7. Check Power Supply (High Speed) Turn ignition off. Disconnect cooling fan relays No. 2 and 3. (Scheme 34) Turn ignition on. Using a voltmeter, measure voltage as follows: Between ground and cooling fan relay No. 2 harness connector terminal No. 1 (Green/Yellow wire). Between ground and cooling fan relay No. 2 harness connector terminal No. 3 (White/Green wire). Between ground and cooling fan relay No. 3 harness connector terminal No. 1 (Green/Yellow wire). Between ground and cooling fan relay No. 3 harness connector terminal No. 3 (White/Green wire). If continuity is present at each circuit check, go to next step. If continuity is not present at any circuit check, repair fault in circuit and retest system.
8. Check Ground Circuits (High Speed) Turn ignition off. Disconnect cooling fan motor No. 1 and 2 harness connectors. (Scheme 35) Using an ohmmeter, check continuity as follows: Between cooling fan relay No. 2 harness connector terminal No. 5 (White/Blue wire) and cooling fan motor No. 1 harness connector terminal No. 2 (White/Blue wire). Between cooling fan relay No. 2 harness connector terminal No. 6 (White/Red wire) and cooling fan motor No. 1 harness connector terminal No. 3 (White/Red wire). Between cooling fan relay No. 2 harness connector terminal No. 7 (Black wire) and ground Between cooling fan relay No. 3 harness connector terminal No. 5 (White/Blue wire) and cooling fan motor No. 2 harness connector terminal No. 2 (White/Blue wire). Between cooling fan relay No. 3 harness connector terminal No. 6 (White/Red wire) and cooling fan motor No. 2 harness connector terminal No. 3 (White/Red wire). Between cooling fan relay No. 3 harness connector terminal No. 7 (Black wire) and ground If continuity is present at each circuit check, go to next step. If continuity is not present at any circuit check, repair fault in circuit and retest system.
9. Check Output Signal Circuit (High Speed) Disconnect ECM harness connector. see scheme 2 Using an ohmmeter, check continuity between ECM harness connector terminal No. 13 and cooling fan relay No. 2 and No. 3 connector Light Green wire. If continuity is not present at any circuit check, repair fault in circuit and retest system. If continuity is present at each circuit check, check wiring harness and connectors for damage or corrosion and repair if necessary. If no faults are found, replace cooling fan relays and retest system. If fault is still present, replace cooling fan motor.

Scheme 34

Scheme 35