0128740 JOHNSON BUSHING, Thrust

Table 1
Diagnostic Codes Table    
Description     Conditions which Generate this Code     System Response    
544-8 Engine Cooling Fan Speed Sensor abnormal frequency, pulse width, or period     The engine speed is equal to or greater than low idle but less than 2400 rpm for one minute.
The fan speed is less than 38 rpm or the fan speed is greater than 2000 rpm for two seconds.     The warning lamp will illuminate, if equipped.
The code is logged.    The fan speed sensor is a digital sensor that provides a speed signal from the engine cooling fan to the Electronic Control Module (ECM). The ECM controls the speed of the fan by varying the current to the fan speed solenoid. The ECM attempts to keep the fan within 50 rpm of the desired fan speed.The fan speed sensor receives a regulated 8.0 0.5 VDC supply voltage from the ECM. The fan speed sensor provides a pulse width modulated signal to the ECM that represents the speed of the fan. The frequency range of the output represents fan speeds from 50 rpm to 1800 rpm.Note: Refer to Troubleshooting, "Sensor Supply - Test" if the ECM has detected a problem with the digital sensor supply voltage.
Illustration 1 g01393234
Schematic for the fan speed sensorTest Step 1. Inspect Electrical Connectors and Wiring
Remove electrical power from the ECM.
Illustration 2 g01139425
ECM (1) J1/P1 connectors (2) J2/P2 connectors
Thoroughly inspect ECM connector J1/P1, ECM connector J2/P2, and all other connectors in the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 3 g01394757
P1 terminals that are associated with the cooling fan speed (P1-29) Sensor return (P1-35) +8 V digital supply
Illustration 4 g01394760
P2 terminal that is associated with the cooling fan speed (P2-25) Engine fan speed
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the Cat Data Link.
Check the allen head screw on each ECM connector for the proper torque. Also, check the allen head screw on the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.Expected Result:All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points.Results:
OK - The harness and connectors appear to be OK. Proceed to Test Step 2.
Not OK - There is a problem with 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 completely coupled. Verify that the repair eliminates the problem.STOPTest Step 2. Check the Status of the Engine Fan Speed with Caterpillar Electronic Technician (ET)
Connect Cat ET to the service tool connector.
Restore electrical power to the ECM. Start the engine.
Compare the status for "Engine Fan Speed" to the status for "Desired Engine Fan Speed" on ET.
Remove electrical power from the ECM.Expected Result:"Engine Fan Speed" is within 50 rpm of "Desired Engine Fan Speed".Results:
OK - The engine fan speed is within the desired rpm range.Repair: The sensor is operating correctly. There may be an intermittent electrical problem in a connector or in the harness. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - The engine fan speed is not within the desired rpm range. Proceed to Test Step 3.Test Step 3. Check the Digital Sensor Supply Voltage at the Sensor Connector
Disconnect the connector for the engine cooling fan speed sensor.
Restore electrical power to the ECM.
Measure the voltage across terminal A (+8 V digital supply) and terminal B (sensor return).
Disconnect the connector for the engine cooling fan speed sensor.
Remove electrical power from the ECM.Expected Result:The digital sensor supply voltage should be 8.0 0.5 VDC.Results:
OK - The supply voltage is reaching the sensor. Proceed to Test Step 4.
Not OK - The supply voltage is not reaching the sensor. Proceed to Test Step 5.Test Step 4. Check for Shorts in the Harness From the Fan Speed Sensor to the ECM
Disconnect the ECM connectors J1/P1 and J2/P2.
Disconnect the connector for the engine cooling fan speed sensor.
Measure the resistance between terminal P1-35 (+8 V digital supply) and chassis ground.
Measure the resistance between terminal P1-35 (+8 V digital supply) and all of the other terminals on the P1 connector.
Measure the resistance between terminal P1-35 (+8 V digital supply) and all of the terminals on the P2 connector.
Measure the resistance between terminal P2-25 (engine fan speed) and chassis ground.
Measure the resistance between terminal P2-25 (+8 V digital supply) and all of the other terminals on the P2 connector.
Measure the resistance between terminal P2-25 (+8 V digital supply) and all of the terminals on the P1 connector.Expected Result:The resistance for each measurement indicates an open circuit.Results:
OK - The resistance measurement indicates an open circuit. Proceed to Test Step 5.
Not OK - The resistance measurement indicates there is a short between the ECM and the fan speed sensor.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 5. Check for Open Circuits in the Harness From the Fan Speed Sensor to the ECM
Remove electrical power from the ECM.
Disconnect the ECM connectors J1/P1 and J2/P2.
Use a suitable piece of wire to short terminal P1-35 (+8 V digital supply) and terminal P1-29 (sensor return).
Disconnect the connector for the engine cooling fan speed sensor.
Measure the resistance between terminal A (+8 V digital supply) and terminal B (sensor return).
Use a suitable piece of wire to short terminal P2-25 (+8 V digital supply) and terminal P1-29 (sensor return).
Measure the resistance between terminal C (engine fan speed) and terminal B (sensor return).Expected Result:The resistance measurements do not indicate an open circuit.Results:
OK - The resistance measurements do not indicate an open circuit. Proceed to Test Step 6.
Not OK - There is an open circuit in the wiring harness between the fan speed sensor and the