Circuit Description
The cooling fan system in this vehicle provides for two separate modes of operation. These are the low speed fan and the high speed fan operating modes. The low speed mode operates both fans at half speed by using a series circuit configuration. The high speed mode operates both fans at full speed by using a parallel circuit configuration. These two operating modes are accomplished using three fan control relays.
This system which uses three relays to control two fan motors appears complicated. To aid in better understanding this system it is suggested to follow the circuits in the schematic as you read the description. This will aid in understanding the two distinct modes of operating the relays and coolant fans.
Low speed fan operation is established when the powertrain control module (PCM) commands fan relay #1 ON by providing a ground circuit with an internal driver. Relays #2 and #3 are left OFF. This closes the relay switch and allows current to flow from the battery, through the switch contacts to the cooling fan #2. Current flow continues out of the fan motor #2 to relay #3. The unenergized relay #3 switch contacts allow current to flow to relay #2 and fan motor #1. This provides power to the cooling fan #1 motor. The low side of cooling fan #1 completes the circuit to ground. This circuit is a series circuit which allows half speed operation for each fan since each fan motor will use half of the supplied battery power.
High speed operation is established when all three relays are energized. relays #2 and #3 share the same control circuit to the PCM. As in the low speed mode, relay #1 supplies current flow to cooling fan #2. Current flow continues through the motor to relay #3 which is now energized. The switch has now provided a path for current to flow directly to ground. This circuit now only has the fan motor #2 to power and allows it to run at full speed. Relay #2 is also energized and provides current flow to the cooling fan #1. This fan now has its own dedicated circuit and will operate at full speed. This mode is operating as a parallel circuit.
Conditions for Running the DTC
| • | The engine speed is more than 400 RPM. |
| • | The ignition voltage is between 6.0 volts and 18.0 volts. |
Conditions for Setting the DTC
| • | The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match. |
| • | The conditions must be present for a minimum of 5 seconds. |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
Important:
• Remove any debris from the PCM connector surfaces before servicing
the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the
PCM. Ensure that the gaskets are installed correctly. The gaskets prevent
water intrusion into the PCM. • For any test that requires probing the PCM or a component
harness connector, use the J 35616
connector test adapter kit. Using this kit prevents damage
to the harness and component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
For an intermittent, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Listen for an audible click when the relay operates. Command both the ON and the OFF states. Repeat the commands as necessary.
-
This test can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm, the coil may open (Amps drop to 0), or short (goes above 0.75 Amp).
-
Identify and test the relay coil terminals in order to avoid improper diagnosis.
-
Listen for an audible click as the relay operates. Repeat the procedure as necessary.
-
If you do not find any trouble in the control circuit or the connection at the PCM, the PCM may be faulty. However, this is an extremely unlikely failure.
-
The repair is not complete if the scan tool indicates that the diagnostic ran and failed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the relay turn ON and OFF when commanded? | -- | |||
Important: If the DMM goes to 0, replace the relay. Does the current draw measure less than the specified value shown? | 0.75A | Go to Diagnostic Aids | ||
4 |
Does the DMM display infinite resistance? | -- | ||
|
Important: For underhood electrical center relay terminal identification refer to Electrical Center Identification Views in Engine Electrical.
Does the test lamp turn ON and OFF with each command? | -- | |||
6 | Probe the FC relay 1 B+ supply circuits at the Fuse/Relay Center Box 1 using the test lamp connected to ground. Is the test lamp illuminated? | -- | ||
Does the relay turn ON when the circuit is grounded and OFF when the circuit is opened? | -- | |||
8 |
Did you find and correct the condition? | -- | ||
9 |
Did you find and correct the condition? | -- | ||
10 | Repair the relay control circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
11 | Repair the relay B+ supply circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
12 | Replace the relay. Refer to Cooling Fan Relay Replacement in Engine Cooling. Is the action complete? | -- | -- | |
|
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
Does the scan tool indicate that this test passed? | -- | |||
15 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
