Cooling Fan Inoperative (LCD, LBX or LBS)
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Cooling Fan Inoperative (LCD, LBX or LBS)
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Diagnostic Fault Information
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Cooling Fan Left High Speed Relay
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Circuit
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Short to Ground
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High Resistance
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Open
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Short to Voltage
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Signal Performance
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Relay Coil Ignition
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P0691 00
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P0691 00
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P0480 00
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-
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-
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Relay Switch B+
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1
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1
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1
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-
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-
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Relay Coil Control
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P0691 00
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P0691 00
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P0480 00
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P0692 00
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-
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Relay Output Control
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1
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1
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1
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2
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-
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1. Low and Medium Speed Fan Inoperative without a DTC
2. Medium Speed Fan Always ON without a DTC
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Cooling Fan Left Low Speed Relay, Cooling Fan Speed Control Relay and Cooling Fan Right Low Speed Relay
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Circuit
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Short to Ground
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High Resistance
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Open
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Short to Voltage
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Signal Performance
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Relay Coil Ignition
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P0693 00
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P0693 00
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P0481 00
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-
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-
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Relay Switch B+
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1
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1
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1
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-
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-
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Relay Coil Control
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P0693 00
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P0693 00
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P0481 00
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P0694 00
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-
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Relay Output Control
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1
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1
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1
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2
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-
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1. Fans Inoperative without a DTC
2. Medium Speed Fan Always ON without a DTC
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Cooling Fan Medium Speed Relay
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Circuit
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Short to Ground
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High Resistance
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Open
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Short to Voltage
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Signal Performance
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Relay Coil Ignition
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P0695 00
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P0695 00
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P0482 00
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-
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-
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Relay Switch B+
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1
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1
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1
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-
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-
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Relay Coil Control
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P0695 00
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P0695 00
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P0482 00
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P0696 00
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-
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Relay Output Control
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1
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1
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1
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2
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-
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1. High Speed Fan Inoperative without a DTC
2. High Speed Fan Always ON without a DTC
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Circuit/System Description
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The engine control module (ECM) commands the fans ON in either high speed, medium speed, or low speed, depending on cooling requirements.
Low Speed
In low speed operation, the ECM applies ground to the coil side of the following relays with the cooling fan relay 1 control circuit:
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Cooling Fan Left Low Speed Relay
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•
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Cooling Fan Right Low Speed Relay
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•
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Cooling Fan Speed Control Relay
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This energizes the relay coils. The low speed cooling fan relays supply power to the appropriate cooling fan motor through an internal fan resistor. The fan speed control relay contacts close and supply a direct ground path for the left cooling fan motor. The right cooling fan motor is connected to a dedicated ground. This results in both fans operating at low speed.
Medium Speed
In medium speed operation, the ECM commands the low speed fan relays, and the speed control relay off. The ECM simultaneously commands both of the cooling fan high speed relays on with the cooling fan relay 2 control circuit. The cooling fan motors are supplied power directly from the cooling fan high speed relays. The right cooling fan is connected to a dedicated ground, and operates at high speed. The left cooling fan is supplied a ground through the right cooling fan resistor and fan motor, which is connected to the de-energized cooling fan speed control relay. This results in the right cooling fan operating at a reduced speed.
High Speed
In high speed operation, the ECM applies a ground to the coil side of all five cooling fan relays. When energized, the high speed relays apply voltage directly to the cooling fans through the switch side of the relays. The energized cooling fan speed control relay provides a direct ground circuit for the left cooling fan. This arrangement allows each fan to receive full voltage and operate at high speed.
Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation (Diesel)
Cooling Fan Description and Operation (LDK/A20NHT, LBW/A28NER, LAU/A28NET )
Electrical Information Reference
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Circuit/System Verification
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1.
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Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0480, P0481, P0482, P0691, P0692, P0693, P0694, P0695 or P0696 are not set.
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3.
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Ignition ON, command the appropriate fan relay ON and OFF with a scan tool. Verify that the fans turn ON and OFF when changing between the commanded states.
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1.
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Ignition OFF, disconnect all five cooling fan relays.
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2.
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Test for less than 5 Ω between the KR20E Cooling Fan Speed Control Relay terminal 8 and ground.
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3.
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If greater than the specified range, test the ground circuit for an open/high resistance.
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4.
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Note
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The following test must performed on all cooling fan relays.
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Ignition ON, verify that a test lamp illuminates between each relay switch B+ circuit terminal and ground.
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5.
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If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the appropriate cooling fan motor.
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6.
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Ignition OFF, connect a jumper wire between the KR20E Cooling Fan Speed Control Relay terminal 2 and the relay ground circuit terminal 8.
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7.
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Note
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The following test must be performed on both cooling fan low speed relays.
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Connect a 20 A fused jumper between the cooling fan low speed relay switch B+ circuit terminal 2 and the relay controlled output circuit terminal 8. Ignition ON, verify the cooling fan is activated.
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8.
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If the fan does not activate, test the following conditions and repair as necessary.
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Relay controlled output circuit for a short to ground or an open/high resistance
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Open cooling fan resistor
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Open circuit between the G10L Cooling Fan Motor - Left terminal 3 and the KR20E Cooling Fan Speed Control Relay terminal 2
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Fan ground circuit for an open/high resistance
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9.
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Note
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The following test must be performed on both cooling fan high speed relays.
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Ignition OFF, remove the low speed fan relay jumper wire. Connect a 20 A fused jumper between the cooling fan high speed relay switch B+ circuit terminal 2 and the relay controlled output circuit terminal 8. Ignition ON, verify the cooling fan is activated.
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10.
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If the fan does not activate, test the relay controlled output circuit for a short to ground or an open/high resistance.
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11.
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Ignition ON, verify that the left cooling fan is activated.
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12.
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If the left cooling fan does not activate test the relay controlled output circuit for an open/high resistance.
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13.
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If all circuits test normal, test or replace the relay.
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Relay Test
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1.
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Ignition OFF, disconnect the cooling fan relay.
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2.
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Test for 70-110 Ω between terminals 4 and 6.
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3.
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If the resistance is not within the specified range, replace the relay.
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4.
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Test for infinite resistance between the following terminals:
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5.
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If not the specified value, replace the relay.
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6.
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Install a 20 A fused jumper wire between relay terminal 4 and B+. Install a jumper wire between relay terminal 6 and ground. Test for less than 2 Ω between terminals 2 and 8.
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7.
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If greater than the specified range, replace the relay.
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8.
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Note
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This step is only for the KR20E Cooling Fan Speed Control Relay.
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9.
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Remove the jumper wires. Test for less than 2 Ω between terminals 2 and 5.
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10.
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If greater than the specified range, replace the relay.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
