HOSE AS 1078147 - Caterpillar

System Operation Description:Use this procedure to troubleshoot suspected problems with the engine speed control.Note: For this troubleshooting procedure, the Desired Speed Input configuration parameter must be set to "0-5 VDC". 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 "0-5 VDC Input" setting configures the ECM to receive a 0-5 VDC signal for the desired engine speed. If the Desired Speed Input is set to "4-20 mA Input", refer to Troubleshooting, "Speed Control (4 - 20 mA) - Test" for details related to troubleshooting that speed control.The desired speed potentiometer is used to establish the setpoint for the desired engine speed for the engine.The potentiometer is powered with 5 VDC that is provided by the Electronic Control Module (ECM). A ground circuit for the potentiometer is also provided by the ECM. The speed control utilizes a 0-5000 Ohm linear taper potentiometer to provide a signal to the ECM. The potentiometer varies the resistance linearly through ten turns of the adjusting rod. As the adjusting rod is turned, the load that is created by the potentiometer is varied. This circuit load is detected by the ECM and is equated to a setpoint for desired engine speed.
Illustration 1 g02336257
Desired speed potentiometer (1) Potentiometer (2) Adjusting rod (3) Engine speed dialAn 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 0-5 VDC 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 0-5 VDC 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".A 262-3 diagnostic code will be activated if either of the following conditions occur:
A short in the wiring for the desired speed signal to a voltage that is greater than +5 VDC
Adjustment of the desired speed potentiometer near the maximum desired speedA 262-4 diagnostic code will be activated if either of the following conditions occur:
A short in the wiring for the desired speed signal to ground
Adjustment of the desired speed potentiometer near the minimum desired speedThis troubleshooting procedure may generate additional diagnostic codes. Continue to troubleshoot the original problem before troubleshooting other codes. Clear the diagnostic codes after the problem is resolved.
Illustration 2 g02336318
Schematic for the desired speed potentiometerTest Step 1. Inspect the Electrical Connectors and the Wiring
Place the Engine Control Switch (ECS) in the OFF/RESET position.Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
Illustration 3 g01393766
Location