C27 and C32 Engines for Caterpillar Built Machines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the cooling fan control solenoid. Also, use this procedure if one of the diagnostic codes in Table 1 is active.

Table 1

CDL Code and Description	Conditions which Generate this Code	System Response
291-5 Engine Cooling Fan Solenoid current below normal	The Electronic Control Module (ECM) detects an open circuit and/or a short to the +Battery in the circuit for the cooling fan control solenoid.	The ECM sends minimum current to the fan control solenoid. The code is logged.
291-6 Engine Cooling Fan Solenoid current above normal	The ECM detects a short circuit to ground in the circuit for the cooling fan control solenoid.

Illustration 1	g02307434
Location of the cooling fan control solenoid (left rear engine view) (1) Pump (2) Cooling fan control solenoid

The ECM controls the rpm of the engine fan in order to provide the following benefits:

• Increased productivity

• Reduced noise from the fan

• Improved fuel economy

• Reduced overcooling of the engine

The fan control solenoid controls the displacement of the hydraulic pump that supplies pressurized oil to the fan motor. The ECM controls the speed of the fan by controlling the current to the fan control solenoid. The current to the cooling fan control solenoid varies between 0.12 (maximum fan rpm) to 1.30 A (minimum fan rpm). The fan is controlled to maintain a speed between 485 (minimum fan rpm) to 1107 rpm (maximum fan rpm). The ECM continuously adjusts the current to the cooling fan control solenoid. This control ensures that the fan rpm remains within ± 50 rpm of the desired rpm.

The engine cooling fan pump pressure sensor provides feedback to the ECM about the hydraulic oil pressure that is available at the fan pump. The ECM compares this feedback signal to a set of maps that are stored in the software. The maps are used by the ECM to calculate the desired fan drive pump pressure. If the actual pump pressure is different from the calculated pressure, the ECM will vary the current to the cooling fan control solenoid. The ECM controls the pump pressure to match this calculated pressure.

Cooling fan control is suspended until the following conditions are met:

• Engine coolant temperature is greater than 90° C (194° F)

• Outlet temperature of the ATAAC is greater than 50° C (122° F)

• Hydraulic oil temperature is greater than 90° C (194° F)

During cooling fan control, the following conditions are targeted by the engine ECM:

• An engine coolant temperature that is equal to 104° C (219° F)

• An outlet temperature for the ATAAC that is equal to 55° C (131° F)

• A hydraulic oil temperature that is equal to 95° C (203° F)

The ECM monitors engine coolant temperature and intake manifold air temperature in order to determine the correct fan rpm. When a system fault is detected, fan rpm is increased. When the engine is lugging, the fan rpm is reduced in order to reduce the load on the engine. The speed of the fan is also reduced during high altitude operation.

An override is available with Caterpillar Electronic Technician (ET). The override allows the fan to be manually changed from the minimum to the maximum rpm. If the ECM detects a problem with the solenoid circuit, a diagnostic code is generated. If the ECM detects a system fault, the ECM provides minimum current to the solenoid. This current ensures a maximum fan speed while the fault condition exists. The ECM will generate diagnostic code for the fault.

Illustration 2	g01415855
Schematic for the cooling fan control solenoid

Illustration 3	g02307595
Location of the J1/P1 ECM connectors

Illustration 4	g01415857
P1 ECM connector (P1-43) Cooling fan control solenoid (P1-51) Solenoid return

Illustration 5	g01155187
Terminal locations at the connector for the cooling fan control solenoid (Terminal 1) Power to the solenoid (Terminal 2) Return

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the keyswitch to the OFF position. B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect". C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit. E. Check the harness and the wiring for abrasion and for pinch points.	Electrical Connectors and Wiring	Result: The harness and wiring appear to be OK. Proceed to Test Step 2. Result: There is a problem in the connectors and/or wiring. Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the repair eliminates the problem.
2. Check for Codes A. Connect Cat® Electronic Technician (ET) to the service tool connector. B. Determine if a code is active or logged.	Codes	Result: No diagnostic codes are active. Repair: The problem may have been related to a faulty connection in the harness. Carefully inspect the connectors and wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect". Verify that the repair eliminated the problem. Result: A short circuit diagnostic code -6 is active at this time. Proceed to Test Step 3. Result: An open circuit diagnostic code -5 is active at this time. Proceed to Test Step 4.
3. Create an Open Circuit at the Cooling Fan Control Solenoid A. Turn the keyswitch to the OFF position. B. Disconnect the connector for the cooling fan control solenoid. C. Turn the keyswitch to the ON position. D. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. E. Select diagnostic tests from Cat ET. F. Select the "Override Parameters" screen on Cat ET. G. Activate the fan override. H. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic code to become active. I. Disable the fan override.	Open Circuit	Results: A short circuit diagnostic code -6 was active before disconnecting the connector. An open circuit diagnostic code -5 became active after disconnecting the connector. Repair: Temporarily connect a new cooling fan control solenoid to the harness, but do not install the new cooling fan control solenoid. Verify that there are no active diagnostic codes for the cooling fan control solenoid. If there are no active diagnostic codes for the cooling fan control solenoid, permanently install the new cooling fan control solenoid. Clear any logged diagnostic codes. Verify that the repair eliminated the problem. Result: A short circuit diagnostic code -6 remains active when the connector for the cooling fan control solenoid is disconnected. There is a short circuit between the harness connector for the cooling fan control solenoid and the ECM. Proceed to Test Step 5.
4. Create a Short at the Connector for the Cooling Fan Control Solenoid A. Turn the keyswitch to the OFF position. B. Fabricate a jumper wire that is long enough to create a short between the terminals of the connector for the cooling fan control solenoid. Crimp connector pins to each end of the jumper wire. C. Install the jumper wire between terminal 1 (cooling fan control solenoid) and terminal 2 (return) on the harness side of the connector. D. Turn the keyswitch to the ON position. E. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. F. Select diagnostic tests from Cat ET. G. Select the "Override Parameters" screen on Cat ET. H. Activate the fan override. Activate the fan override. I. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic code to become active. J. Disable the fan override. Remove the jumper wire.	Short Circuit	Result: A short circuit diagnostic code -6 is active when the jumper wire is installed. An open circuit diagnostic code -5 is active when the jumper wire is removed. Repair: The engine harness and the ECM are OK. Temporarily connect a new cooling fan control solenoid to the harness, but do not install the new cooling fan control solenoid. Verify that there are no active diagnostic codes for the cooling fan control solenoid. If there are no active diagnostic codes for the cooling fan control solenoid, permanently install the new cooling fan control solenoid. Clear any logged diagnostic codes. Verify that the repair eliminated the problem. Result: The open circuit diagnostic code -5 remains active with the jumper in place. The open circuit is between the ECM and the connector for the cooling fan control solenoid. Proceed to Test Step 5.
5. Check the ECM for Proper Operation A. Disconnect the J1/P1 ECM connector. B. Fabricate a jumper wire that is long enough to create a short between the ECM connector and engine ground. Crimp a connector socket to one end of the jumper wire. C. Remove the wire from terminal location P1-43 (cooling fan control solenoid) at the ECM connector. Install the jumper wire into this terminal location. D. Connect the J1/P1 ECM connector. E. Create an open at the ECM. F. Create a short at the ECM. G. Restore all wiring to the original configuration.	-5 and -6 Codes	Result: An open circuit diagnostic code -5 is active when the jumper wire creates an open circuit. A short circuit diagnostic code -6 is active when the jumper wire for the solenoid is shorted to engine ground. Repair: The ECM is operating properly. The problem is in the harness wiring between the ECM and the connector for the cooling fan control solenoid. There may be a problem in one of the connectors. Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the repair eliminated the problem. Result: One of the following conditions exists: The open circuit diagnostic code -5 is not active when the jumper wire creates an open circuit. The short circuit diagnostic code -6 is not active when the jumper wire is shorted to engine ground. Repair: There appears to be a problem with the ECM. Before you consider replacing the ECM, consult with the Dealer Solutions Network (DSN) for assistance. Verify that the repair eliminated the problem.