Unreliable Faults Are Found With Body Position Sensors On Off Highway Trucks{1408, 1439} Caterpillar

Off-Highway Truck/Tractor:

785C (S/N: APX301-UP; 5AZ274-UP)

789C (S/N: 2BW556-UP)

793C (S/N: ATY502-UP)

793D (S/N: FDB1-UP)

Introduction

This Technical Information Bulletin replaces Technical Information Bulletin, TIBU5532 20 October, "Unreliable Faults Are Found With Body Position Sensors On Off Highway Trucks.". Disregard the 20October 2008 Technical Information Bulletin. Refer to the following information.

Problem

The 198-8372 Position Sensor Gp (ROTARY) is used to detect the position of the dump body on large off-highway trucks. Failure analysis of 198-8372 Position Sensor Groups (ROTARY) that have been returned from the field has not revealed any problems with the majority of sensors.

Solution

Use the calibrations that are listed below in order to verify if there is a failure with the 198-8372 Position Sensor Gp (ROTARY) .

Troubleshooting Information

Communicate failures of the parts that are listed above to Caterpillar Electronics Product Analyst at (309) 494-0744 when you begin troubleshooting the sensor. Also, the Caterpillar Electronics Product Analyst can be contacted at the following e-mail address: "West_Michael_J@cat.com". This information will help Caterpillar better understand the reason that these sensors are being replaced. Please have the following information when you contact the Product Analyst.

• VIMS data logger that contains the active fault code

• Event summaries from Caterpillar Electronic Technician (Cat ET)

• The service history of the truck body and body pivot pin may affect the data. Other factors that may affect the data include the following: The pivot pins have been replaced and/or serviced. The body has been serviced and/or replaced.

• Record of any problems with the linkage assembly that connects the sensor to the body

• Any other information that is pertinent in the troubleshooting of this problem

Calibration Procedures

The calibration procedure must be performed when one or more of the following conditions occur:

• A new truck is being assembled.

• A new position sensor is installed.

• The ECM is replaced.

• The body is replaced.

The position sensor is located near the pivot pin for the dump body. A lever is attached between the sensor and the dump body. When the dump body is raised or lowered, the lever rotates the sensor. This action changes the Pulse Width Modulation signal (PWM signal) that is sent to the Chassis Electronic Control Module (Chassis ECM).

If the expected PWM signal does not occur, then the Chassis ECM generates an event code. The code is logged to the Vital Information Management System (VIMS).

Do not attempt any procedure until you have read the information and you understand the information that is in this special instruction.

Full Lower Calibration

Required Conditions

The following conditions must be met for 12 seconds:

• The engine is running with no ground speed.

• The payload is zero.

• The hoist control lever must be in FLOAT mode.

• The duty cycle output is within the range of 3 percent to 30 percent.

Note: The recommended duty cycle output is within the range of 14 percent to 19 percent.

When all of the conditions have been met for 12 seconds, the value of the calibration will be the average of the values that were recorded during that period of time.

Expected Values

When the bed is fully lowered, the Chassis ECM expects a value that is greater than 1 percent PWM.

If the expected PWM value is not obtained, then an FMI-04 will be logged. If this event occurs, then perform the ""Rod Adjustment" " in the ""Maintenance Procedures" " section.

Tolerance Range

The standard range for the calibration limits is plus or minus 2 percent of the last calibration point. If the tolerance range is not exceeded, then the lower calibration point will not change.

If the tolerance range is exceeded, then the upper calibration point will default to a 50 percent duty cycle until the upper calibration is performed. The lower calibration point will change to the average value.

This change occurs because there has been a mechanical change in the system that measures the output of the sensor. For example, a change could occur under any of the following conditions:

• The nuts that secure the adjustment rod are loose.

• There is excessive wear on the body pins.

• The adjustment rod is bent or damaged.

• The sensor is damaged.

Any of these conditions could affect the duty cycle of the full lower calibration.

Full Raise Calibration

Required Conditions

The following conditions must be met for 500 milliseconds:

• The engine is running with no ground speed.

• The duty cycle output is in a range of 50 percent to 95 percent.

• The current full up duty cycle must be greater than the previous full up duty cycle.

• The hoist control lever must be in RAISE mode or in HOLD mode.

Note: When the bed has reached the maximum height, the operator should move the hoist lever from the RAISE position to the HOLD position. Five seconds after the hoist lever is in position the calibration will begin.

When all of the conditions have been met for 500 milliseconds, the value of the calibration will be the average of the values that were recorded during the 500 milliseconds. If the current upper calibration value is less than the previous upper calibration value, then the value will not change.

Expected Values

When the bed is fully raised, the Chassis ECM expects a value of less than 96 percent PWM.

If the expected PWM value is not obtained, then an FMI-03 will be logged. If this event occurs, then perform the ""Rod Adjustment" " in the ""Maintenance Procedures" " section.

Maintenance Procedures

Rod Adjustment

Illustration 1	g01651313
Typical rod linkage (1) Rod end (2) Nut (3) Centers of the rod ends (4) Rod

The following adjustment may be required in order for the Chassis ECM to calibrate the position sensor:

1. Disconnect rod (4) from the dump body.

2. Loosen nut (2) on rod (4) .

3. Twist the rod (4) in order to obtain a distance of 360.0 ± 3.0 mm (14.17 ± 0.12 inch) between the centers of the rod ends (3) .

4. Tighten nut (2) .

5. Reattach rod (4) to the dump body.

Angle Verification

When a new sensor, a new body, or a new ECM is installed on the truck, verify that the angle of the dump body is within tolerance. If the angle is not within tolerance, then the Chassis ECM cannot correctly calibrate the position sensor.

1. Lower the body to the frame rails.

2. Press "OK" on the VIMS until the time, the date, and the machine hours are displayed. This action ensures that all events have been accepted.

3. Enter a value of "724".

4. Press the "Gauge" button that is located on the far left side of the keypad. The Message Center displays the degrees of the angle of the body.

   If the value is less than 7 degrees, the software in the Chassis ECM calibrates the sensor. The calibration is performed automatically by the Chassis ECM when the body is raised and lowered.

   If the value is not less than 7 degrees, then perform the ""Rod Adjustment" " in the ""Maintenance Procedures" " section.

Modification of the snubbing

Modifying the value of the snubbing will alter the time that is required for the body to drop completely to the frame once snubbing occurs. The snubbing is changed by using the Capterpillar Electronic Technician (Cat ET). The value that is changed is the Hoist Lower Valve Adjustment Status (HLVAS).

To modify the snubbing, perform the following steps:

1. Go to the "Configuration" screen.

2. Select "TRANSMISSION ECM".

3. Find the group that contains the "HLVAS" value that will be changed. Double click the value.

4. Modify the value according to Table 1. The value can be in a range from "+5" to "-5".
   Show/hide table

   Table 1

   Value	Result
   +5	Snubbing will occur later or snubbing will occur at a lower angle. The body could hit the rails of the frame with force.
   0	Default value
   -5	Snubbing will occur earlier or snubbing will occur at a greater angle. The bed may not sit on the frame.

Known Issues

The following issues could prevent calibration of the position sensor. The issues could cause sensor diagnostics to be logged.

Wear on the Body Pins

Wear on the body pins could cause the position sensor to provide an incorrect value. This value could cause diagnostic faults to register against the sensor.

If the body pins are worn, perform the ""Rod Adjustment" ". Verify that the angle of the body is less than 7 degrees when the body is fully lowered.

The Body Does Not Drop Fully

The body may not drop fully to the frame rails. By using Cat ET, adjust the "HLVAS" value. Perform a complete cycle of body up and body down. Continue to adjust the "HLVAS" value until the desired snubbing is obtained.

Note: Snubbing is adjusted automatically by a calculation that is made by the Chassis ECM. The value for the calculation is derived from the calibrated signal from the dump body position sensor. Adjusting the "HLVAS" value is only necessary when further adjustments are required.