• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
The engine control module (ECM) grounds the low speed relay, which is relay 1, and the high speed relay, which is relay 2, control circuits through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the ECM. When the ECM is commanding a component ON, the voltage potential of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the ECM detects that the actual state of the control circuit does not match the expected state, a DTC will set.
Cooling Fan Description and Operation
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
⇒ | If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the fan does not activate and the circuits test normal, replace the fan. |
⇒ | If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary. |
⇒ | If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary. |
Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that each fan turns ON and OFF with each command.
Table 1: | COOL FAN 1 Relay |
Table 2: | COOL FAN 2 Relay |
Table 3: | COOLING FAN 3 Relay |
• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
The powertrain control module (PCM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. In high speed, both fans are turned ON at full speed.
In low speed operation, the PCM applies a ground to the coil side of the cooling fan 1 or low speed relay. This energizes the coil and applies voltage directly to the left or low speed cooling fan through the switch side of the relay. The left or low speed cooling fan is connected in series to the right or high speed cooling fan through the normally closed contacts of the cooling fan 3 or the cooling fan control relay. The series circuit operates both fans at low speed.
In high speed operation, the PCM applies a ground to the coil side of all three cooling fan relays. This action applies voltage directly to the right or high speed cooling fan through the switch side of the cooling fan 2 or high speed relay. Simultaneously, the cooling fan 1 or low speed relay provides voltage to the left or low speed cooling fan, while the cooling fan 3 or control relay provides a direct path to ground for the left or low speed cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.
The following two tables illustrate the COOLING FAN 1 relay and the COOLING FAN 2 relay terminal locations in the underhood fuse block. The third table illustrates the COOLING FAN 3 relay terminal locations in the relay electrical connector.
Terminal Identification | |
---|---|
Cooling Fan Supply Voltage | B+ Coil |
Control | B+ Switch |
Front of Vehicle |
Terminal Identification | |
---|---|
Cooling Fan Supply Voltage | B+ Coil |
Control | B+ Switch |
Front of Vehicle |
Terminal Identification | ||
---|---|---|
B+ Coil | Voltage to Right Cooling Fan | Ground |
Voltage from Left Cooling Fan | -- | Control |
Locking Tab |
Cooling Fan Description and Operation
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
⇒ | If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle . |
⇒ | 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 all components connected to the relay switch B+ circuit and replace as necessary. |
⇒ | If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the circuit tests normal, replace the fan. |
Ignition ON, command the fan relays ON and OFF with a scan tool. Verify the appropriate fan turns ON and OFF with each command.