C9 Urban Transit Bus Engine Caterpillar

Powertrain Data Link Circuit - Test

Usage:

C-9 MTB

System Operation Description:

Use this procedure under the following situation:

Use this procedure if one of the following diagnostic codes are active:

231-02 J1939 Data Incorrect (58)
231-12 J1939 Device Not Responding (58)

Also, use this procedure when the Caterpillar Electronic Technician (Cat ET) indicates that the sensor and the ECM are functioning but the engine is not responding to the accelerator pedal position sensor.

The following background information is related to this procedure:

Power train Data Link

The power train data link is designed to offer electronically controlled Anti-Lock Brakes (ABS), traction control systems, and/or transmission controls. This is accomplished by a momentary reduction of engine rpm and/or engine torque, that is triggered by a signal from an off-engine control module for the ABS, the traction control, or the transmission. An off-engine control module is a control module that is not part of the Caterpillar engine control system.

Information from switches may also be transmitted over the J1939 data link. The following parameters can be programmed to send switch information over the J1939 data link:

"Cruise Control On/Off Switch"
"Cruise Control Set/Resume Switch"
"Cruise Pause Switch"
"Service Brake Pedal Position Switch #1"
"Clutch Pedal Position Switch"
"Fan Override Switch"
"Exhaust Brake Switch"
"Diagnostic Enable Switch"
"A/C High Pressure Switch"
"A/C Fan Request Switch"

Any combination of the following systems may be installed together on a vehicle:

Traction Control
Transmission Control
ABS
Switch Information

The required components are installed at the OEM when the vehicle is built.

The sensors for the Power train data link, off-engine control modules, and wiring are installed by the vehicle OEM. Questions that relate to the configuration of the hardware, software, and installation should be referred to to the vehicle OEM.

The J1939 refers to the standard for data link communications of the Society of Automotive Engineers Inc.. The ECM has a customer programmable parameter that is called "Powertrain Data Link" which can be programmed to either of the following options:

"J1939"
"NONE"

Anti-Lock Brake Systems (ABS)

The J1939 data link may be used by an anti-lock brake system (ABS) in order to disable the exhaust brake when the control for the anti-lock brakes determines that the exhaust brake should be disabled. This is usually achieved when the ABS system is active.

Traction Control Systems

Loss of traction is determined by sensors on the vehicle that are mounted near the wheels. These sensors are also used by the ABS system. Typically, a system with traction control includes anti-lock brakes.

Transmission Control

The following characteristics are determined by a vehicle speed sensor in the transmission:

Transmission shift points
Engine rpm
Load

The sensors for power train control provide signals to the vehicle control module of the power train data link. The vehicle control module of the power train data link then communicates with the engine ECM. The engine ECM receives a request from the power train data link. The engine ECM responds by momentarily limiting the following characteristics:

Engine rpm
Torque
Both engine rpm and torque

The presence of an active J1939 data link circuit can be determined by observing the "Powertrain Status" parameter on Cat ET. The status screen on Cat ET will display "INSTALLED" if the proper Personality Module is installed on the ECM, and there is no action that is being requested at that time by any of the control modules on the data link.

If an action is being requested by one of the vehicle control modules, the display will indicate the control that is making the request (traction control or transmission control) or a combination of the two (traction control and transmission control). Power train control is also displayed in the upper right hand corner of the display status screen.

J1939 Data Link

The default programming of the parameter "Powertrain Data Link" is "None". If the data link is required, then the "Powertrain Data Link" parameter must be programmed to "J1939".

Note: The wiring for the J1939 data link is a shielded twisted pair cable and the wiring is not serviceable. The wiring must be replaced when the wiring is damaged.

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Illustration 1	g00830986
Schematic for power train data link

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Illustration 2	g00768550
ECM pin locations

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Illustration 3	g00721539
Terminal locations for ECM

Test Step 1. Inspect Electrical Connectors and Wiring

Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector, the connectors for the power train control module, and the connector terminals for the SAE J1939 data link. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the SAE J1939 Data Link.
Refer to Illustration 3.

Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

Check the harness and wiring for abrasion and pinch points from the data link connectors back to the ECM.

Expected Result:

All connectors, pins and sockets should be completely coupled and/or inserted and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

OK - Proceed to Test Step 2.
Not OK -
Repair: Perform the following repair:Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.
Stop.

Test Step 2. Connect Cat ET and Check for Active Diagnostic Codes

Connect Cat ET to the data link connector.

Turn the key switch to the ON position.

Monitor the active diagnostic code screen of Cat ET. Check and record active diagnostic codes.

Expected Result:

One of the following diagnostic codes is active:

231-02 J1939 Data Incorrect (58)
231-12 J1939 Device Not Responding (58)

Results:

Yes one of the codes is active - Proceed to Test Step 3.
No - Proceed to Test Step 4.

Test Step 3. Use the Special Test on Cat ET to Check the Devices on the J1939 Data Link

Connect Cat ET to the data link connector.

Access the special test "J1939 Receive Communication Status". The special tests are located under the Diagnostic menu.

Cat ET will display the J1939 sources that have transmitted at least one good message that has been successfully received by the ECM. If the ECM has not received any messages from a source, that source will not be displayed. Examples of devices that can use the J1939 data link include the following switches:
- Switches that are programmed to "Instrument Cluster"
- Switches that are programmed to "Body Controller"
- Switches that are programmed to "Cab Controller"

Cat ET will display the J1939 source in the "Description" column. The "Status" column displays the status of the device.

If a message is not received from a device, Cat ET will display "Not Receiving".

The status screen on Cat ET can be set to display the status of a device that is not working. The status screen will display "No Comm" if a message is not received from the device.

Expected Result:

Cat ET displays the devices that are used on the vehicle and the ECM is receiving messages from the devices.

Results:

Yes - The ECM is receiving messages from the devices that are installed on the vehicle. Stop.
No - The ECM is not receiving messages from the devices that are installed on the vehicle.
Repair: The devices that can be programmed to use the J1939 data link can be circuits with two wires or circuits with three wires. Bad connections are the most frequent problem. Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that the connectors are free of corrosion.
Stop.

Test Step 4. Check the Power Train Status Screen on Cat ET

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Illustration 4	g00721856
Typical example of a display screen on Cat ET

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Table 1
Powertrain Status Parameter Group Definition Table
"Heading On Status Screen"	Displayed Message	Definition of Message
"Engine Speed"		Actual engine rpm of the engine
"Percent Torque"		Current engine torque during operation that is expressed as a percent of peak torque
"Powertrain Status"	"Not Installed", "ABS Control", "Traction Control", "Traction and ABS Control", "Trans Control", "Trans and ABS Control", "Trans and Traction Control", "Trans and Traction and ABS"	Communication of the power train control module
"TC Status or Transmission Status"	"No Communication"	Communication from the vehicle control is not being received by the ECM. One of the following conditions exists: The vehicle does not support this feature. The vehicle control is not currently powered, or the wiring is damaged or disconnected.
	"Not Active"	No requests from the Vehicle Power Train ECU (Electronic Control Unit)
	"Speed Command"	Engine rpm is being controlled by a Vehicle ECU.
	"Torque Command"	Engine torque is being controlled by a Vehicle ECU.
	"Speed and Torque Limit"	Engine rpm and torque is being determined by a Vehicle ECU.
	"Torque Limit"	The Torque limit is being determined by a Vehicle ECU.
	"Speed Limit"	The rpm limit is being determined by a Vehicle ECU.
"TC Speed"		The TC Speed is the desired engine rpm setpoint or the engine rpm limit that is being requested by the vehicle's Traction Control ECU.
"TC Torque"		The TC Torque is the desired percent of torque or the desired percent of torque limit that is being requested by the Vehicle's Traction Control ECU.
"Transmission Output Speed"		The Transmission Output Speed is the desired engine rpm setpoint or the engine rpm limit that is being requested by the Vehicle's Traction Control ECU.
"Transmission Torque"		The Transmission Torque is the desired percent of torque or the percent of torque limit that is being requested by the Vehicle's Traction Control ECU.
"ABS Status"	"No Communication"	The ECM is not receiving communication from the vehicle's ABS/Traction Control System. One of the following conditions exists: The vehicle does not support this feature. The vehicle's ABS/Traction Control System is not currently powered. The wiring is damaged or disconnected.
	"Not Active"	There are no requests from the ABS Control.
	"Disable Retarder"	The control for the ABS system requests the operation of the engine retarder to stop.

Connect Cat ET to the data link connector.

While the vehicle is being driven by someone else, monitor Cat ET. Use the following procedure:
1. Access the status screen. Select the "Powertrain Status" screen. The "Powertrain Status" screen relates to the J1939 data link.
1. While the vehicle is being operated, monitor the "Powertrain Status" Screen.
  Refer to Table 1 for an explanation of the parameters that are displayed in the "Powertrain Status" screen of Cat ET.
  Note: Transmission shifts and/or a momentary loss of traction should trigger the display on Cat ET and the appropriate action by the ECM when the correct sensors, controls and wiring are installed on the vehicle.

Expected Result:

The status screen on Cat ET indicates that the ECM is responding to a power train control.

Note: Some power train control modules have test modes that are available by activating diagnostic switches. Ensure that the Caterpillar ECM is not reacting to a test by the power train control module if the problem is related to power train control operation and you believe that the system should not be active.

Results:

Yes - If the response is abnormal, send the vehicle to the OEM dealer for repairs. Stop.
No -
Repair: Perform the following diagnostic procedure:Troubleshooting, "Troubleshooting without a Diagnostic Code"
Stop.