881898 Mercury MOUNT

Illustration 1 g02336257
Desired speed potentiometer
(1) Potentiometer
(2) Adjusting rod
(3) Engine speed dial 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 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 potentiometer
Test 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 of the ECM connectors for the desired speed potentiometer (typical left front engine view)
(1) J1/P1 ECM connectors
Illustration 4 g01393423
Location of the connectors for the desired speed potentiometer (typical left rear engine view)
(2) Interface box
(3) Engine interface connector (40 pin)
Thoroughly inspect ECM connectors (1). Also, thoroughly inspect engine interface connector (3) that is mounted on interface box (2).
Check the allen head screw for each of the ECM connectors for the proper torque.
Illustration 5 g02337277
Terminal locations at the J1/P1 ECM connectors for the desired speed input (analog)
(P1-16) Desired engine speed (0-5 VDC)
(P1-18) +5 V supply
(P1-35) Return
Illustration 6 g02337279
Terminal locations at the engine interface connector for the desired speed input (analog)
(Terminal 6) +5 V Supply
(Terminal 7) Desired engine speed (0-5 VDC)
(Terminal 8) Return
(Terminal 9) Shield
Illustration 7 g02337298
Terminal locations at the desired speed potentiometer
(Terminal 1) Return/shield
(Terminal 2) Desired engine speed (0-5 VDC)
(Terminal 3) +5 V Supply
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the desired speed potentiometer.
Check the harness and wiring for abrasion and for pinch points between the desired speed potentiometer and the ECM. Expected Result:All of the 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. Proceed to Test Step 2.
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.STOPTest Step 2. Check for Diagnostic Codes for the Power Supply
Establish communication between Caterpillar Electronic Technician (ET) and the engine ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary.
Place the ECS in the STOP/COOLDOWN position.
Observe the "Active Diagnostic" screen on Cat ET. Allow 30 seconds for any codes to activate. Look for these codes for the sensor supply:
262-3 5 Volt Sensor DC Power Supply : Voltage Above Normal
262-4 5 Volt Sensor DC Power Supply : Voltage Below NormalExpected Result:There are no active diagnostic codes for the sensor supply.Results:
No Supply Codes Active - There are no active sensor supply diagnostic codes. Neither of the codes are active, but a problem with the desired speed circuit is suspected. Proceed to Test Step 3.
Active 262-3 or 262-4 - There is an active sensor supply diagnostic code.Repair: Check for active cod