ROD AS 1129035 - Caterpillar

System Operation Description:Use this procedure for troubleshooting the following diagnostic codes:
524-3 Desired Engine Speed Sensor : Voltage Above Normal
524-4 Desired Engine Speed Sensor : Voltage Below NormalNote: For this troubleshooting procedure, the Desired Speed Input configuration parameter must be set to "4-20 mA Input". Access the configuration screen in Caterpillar Electronic Technician (ET) by selecting the Service/Configuration drop-down menu. This 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 configures the ECM to receive a 4 to 20 mA signal for the desired engine speed. If the Desired Speed Input is set to" 0-5 VDC Input", refer to Troubleshooting, "Speed Control (Analog) - Test" for details related to troubleshooting that speed control.The value of the signal current corresponds linearly to a range of desired engine speeds between minimum high idle and maximum high idle. The minimum high idle can be adjusted by modifying the Minimum Engine High Idle Speed parameter. The maximum high idle can be adjusted by modifying the Maximum Engine High Idle Speed parameter. For more information, refer to Systems Operation/Testing and Adjusting, "Electronic Control System Parameters".An idle/rated speed switch can be installed on the engine. Terminal P1-28 is configured to receive the signal from the idle/rated speed switch. The idle/rated speed switch is a customer option.When P1-28 is allowed to float (ungrounded circuit), the ECM operates the engine at the minimum engine idle speed. While the input is ungrounded, the 4-20 mA signal is ignored and the engine remains at the minimum idle speed. When P1-28 is grounded to digital return, the ECM controls the engine speed according to the 4-20 mA signal. The engine speed is varied over a linear scale between the Minimum Engine High Idle Speed and Maximum Engine High Idle Speed parameters. For information that is related to troubleshooting the idle/rated speed switch, refer to Troubleshooting, "Engine Speed Switch".If the current in the circuit exceeds 22.0 mA, a 524-3 diagnostic code will be activated. If the current in the circuit falls below 2.0 mA, a 524-4 diagnostic code will be activated.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. Troubleshoot the cause of the original diagnostic code, before troubleshooting any other codes. Clear the diagnostic codes after the problem is resolved.
Illustration 1 g02367756
Schematic diagram of the 4 to 20 mA desired speed inputTest Step 1. Inspect the Electrical Connectors and the Wiring
Set the engine control to the OFF/RESET position.Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
Illustration 2 g01393766
Location of the ECM connectors that are related to the 4 to 20 mA desired speed input