Use this procedure to troubleshoot suspect problems with the circuit for the "4-20 mA Input".
This procedure covers the following diagnostic codes:
- 524-3 Desired Engine Speed Sensor : Voltage Above Normal
- 524-4 Desired Engine Speed Sensor : Voltage Below Normal
Note: For this troubleshooting procedure, the "Desired Speed Input" configuration parameter must be set to "4-20 mA Input" in the "Service/Configuration" screen of Caterpillar Electronic Technician (ET). Do not select "PWM". The Electronic Control Module (ECM) cannot be configured to accept a PWM input signal for control of the engine speed.
The selection of the "4-20 mA Input" setting requires a 4 to 20 mA signal for regulation of the desired engine speed. If the "Desired Speed Input" is set to "0-5 VDC Input", do not use this procedure to troubleshoot the circuit.
When the desired speed input is correspondingly configured, the ECM controls the engine speed according to the 4 to 20 mA current.
The value of the current corresponds to a range of desired engine speeds between minimum high idle and maximum high idle. The "Minimum Engine High Idle Speed" and the "Maximum Engine High Idle Speed" are set with the "Service/Configuration" screen of Cat ET. For more information, refer to Systems Operation/Testing and Adjusting, "Electronic Control System Parameters".
When the "Idle/Rated" switch is in the Rated position, a current value of 4.0 mA corresponds to the programmed "Minimum Engine High Idle Speed". A current value of 20.0 mA corresponds to "Maximum Engine High Idle Speed". Current values within this range will vary the desired engine speed in a linear fashion between "Minimum Engine High Idle Speed" and "Maximum Engine High Idle Speed".
Current values that are greater than 22.0 mA will activate the 524-3 diagnostic code. Current values that are less than 2.0 mA will activate the 524-4 diagnostic code.
The most likely causes of the diagnostic code are a poor connection or a problem in a wiring harness. The next likely cause is a problem with a component. The least likely cause is a problem with the ECM.
Logged diagnostic codes provide a historical record. Before you begin this procedure, use Cat ET to print the logged codes to a file.
The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.
| |
| Illustration 1 | g01325630 |
|
Schematic of the 4 to 20 mA desired speed input | |
Test Step 1. Inspect the Electrical Connectors and Wiring
- Remove the electrical power from the engine.
Note: For the following steps, refer to Troubleshooting, "Electrical Connectors - Inspect".
- Thoroughly inspect the following components:
- J1/P1 connectors
- J6/P6 connectors
- Wiring and the connections between the terminal box and the device that supplies the 4 to 20 mA signal
- Check the torque of the allen head screw for the ECM connectors.
- Check the harness and wiring for abrasion and for pinch points between the device that supplies the 4 to 20 mA signal and the ECM.
Expected Result:
All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.
Results:
- OK - The components are in good condition with proper connections. If you are troubleshooting a 524-3 diagnostic code, proceed to Test Step 2. If you are troubleshooting a 524-4 diagnostic code, proceed to Test Step 5.
- Not OK - The components are not in good condition and/or at least one connection is improper.
Repair: Perform the necessary repairs and/or replace parts, if necessary.
STOP
Test Step 2. Check for an Open Circuit
- Remove the two wires (+ and −) for the 4 to 20 mA signal from the device that supplies the 4 to 20 mA signal.
- Install a jumper wire between the two wires (+ and −) that were removed from the device that supplies the 4 to 20 mA signal.
- Disconnect the P1 connector from the ECM.
- Measure the resistance between terminals P1-36 and P1-37 on the ECM side of the P1 connector.
Expected Result:
The resistance is less than 5 Ohms.
Results:
- OK - The resistance is less than 5 Ohms. The circuit is not open.
Repair: Remove the jumper wire. Insulate the wire leads with electrical tape in order to ensure that the leads do not create a short circuit.
Proceed to Test Step 3.
- Not OK - The resistance is greater than 5 Ohms. There is a problem with a connector and/or the wiring from the P1 connector.
Repair: The problem may be between the P1 connector and the J6 connector. Alternatively, the problem may be between the J6 connector and the device that provides the 4 to 20 mA signal.
Repair the connection and/or the wire, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 3. Check for a Short Circuit to the +Battery at Terminal P1-36
- Verify that the electrical power is removed from the engine.
- Make sure that there is no electrical power to the device that provides the 4 to 20 mA signal.
- Measure the resistance between terminals P1-36 and P1-57 on the ECM side of the P1 connector.
Expected Result:
The resistance is greater than 20,000 Ohms.
Results:
- Yes - The resistance is greater than 20,000 Ohms. The wiring from terminal P1-36 is not shorted to the +Battery side. Do not reconnect any connectors. Proceed to Test Step 4.
- No - The resistance is less than 20,000 Ohms. There is a problem with a connection and/or the wiring from terminal P1-36.
Repair: The problem may be between the P1 connector and the J6 connector. Alternatively, the problem may be between the P6 connector and the device that provides the 4 to 20 mA signal.
Repair the connection and/or the wire, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 4. Check for a Short to Ground at Terminal P1-37
- Verify that the engine control is in the OFF/RESET mode and that the 35 amp circuit breaker is OFF.
- Make sure that the leads of the wires for the 4 to 20 mA signal do not create a short circuit.
- Measure the resistance between the ground strap for the ECM and terminal P1-37.
Expected Result:
The resistance is greater than 20,000 Ohms.
Results:
- Yes - The resistance is greater than 20,000 Ohms. The wiring from terminal P1-37 appears to be OK.
Repair: Reconnect the P1 connector. Reconnect the two wires ("+" and "-") for the 4 to 20 mA signal to the device that supplies the 4 to 20 mA signal.
Proceed to Test Step 7.
- No - The resistance is less than 20,000 Ohms. There is a problem with a connection and/or the wiring that is connected to P1-37.
Repair: The problem may be between the P1 connector and the J6 connector. Alternatively, the problem may be between the P6 connector and the device that provides the 4 to 20 mA signal.
Locate the wire with the short circuit and replace the wire. Verify that the problem is resolved.
STOP
Test Step 5. Check for a Short Circuit to the +Battery Side at Terminal P1-37
- Verify that the engine control is in the OFF/RESET mode and that the 35 amp circuit breaker is OFF.
- Make sure that there is no electrical power to the device that provides the 4 to 20 mA signal.
- Remove the two wires ("+" and "-") for the 4 to 20 mA signal from the device that supplies the 4 to 20 mA signal. Insulate the wire leads with electrical tape in order to ensure that the leads do not create a short circuit.
- Disconnect the P1 connector from the ECM.
- Measure the resistance between terminals P1-37 and P1-57.
Expected Result:
The resistance is greater than 20,000 Ohms.
Results:
- Yes - The resistance is greater than 20,000 Ohms. The wiring from terminal P1-37 is not shorted to the +Battery side. Do not reconnect any connectors. Proceed to Test Step 6.
- No - The resistance is less than 20,000 Ohms. There is a problem with a connection and/or the wiring from terminal P1-37.
Repair: The problem may be between the P1 connector and the J6 connector. Alternatively, the problem may be between the J6 connector and the device that provides the 4 to 20 mA signal.
Repair the connection and/or the wire, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 6. Check for a Short Circuit to Ground at Terminal P1-36
- Verify that the electrical power is removed from the engine.
- Make sure that the ends of the wires for the 4 to 20 mA signal do not create a short circuit.
- Measure the resistance between ground strap (2) and terminal P1-36.
Expected Result:
The resistance is greater than 20,000 Ohms.
Results:
- Yes - The resistance is greater than 20,000 Ohms. The wiring from terminal P1-36 appears to be OK. Do not reconnect any connectors. Proceed to Test Step 7.
- No - The resistance is less than 20,000 Ohms. There is a problem with a connection and/or the wiring from terminal P1-36.
Repair: The problem may be between the P1 connector and the J9 connector. Alternatively, the problem may be between the P9 connector and the device that provides the 4 to 20 mA signal.
Repair the connection and/or the wire, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 7. Check the Device that Provides the 4 to 20 mA Signal
Measure the 4 to 20 mA signal according to the literature that is provided by the OEM of the device that provides the 4 to 20 mA signal. Verify that the correct signal is provided to the ECM.
Verify the correct 4 to 20 mA signal at terminals P1-36 and P1-37.
Expected Result:
The correct 4 to 20 mA signal is provided to the ECM.
Results:
- Yes - The correct 4 to 20 mA signal is provided to the ECM. However, the ECM is not responding correctly to the signal. There may be a problem with the ECM.
Repair: It is unlikely that the ECM is faulty. Exit this procedure and perform this procedure again. If the problem is not resolved, replace the ECM according to Troubleshooting, "ECM - Replace". Verify that the problem is resolved.
STOP
- No - The ECM is not receiving the correct 4 to 20 mA signal. There is probably a problem with the device that provides the 4 to 20 mA.
Repair: Service the device that provides the 4 to 20 mA according to the literature that is provided by the OEM of the device. Verify that the problem is resolved.
STOP