C13 and C15 On-highway Engines Caterpillar

This procedure covers the following codes:

Refer to Troubleshooting, "Vehicle Speed - Calibrate" if the vehicle speed is being calibrated in ppm (pulses per mile) or PPKM (pulses per kilometer).

The following background information is related to this procedure:

The vehicle speed circuit consists of the vehicle speed source and associated wiring. The vehicle speed source is installed by the vehicle OEM. Usually, a sensor reads movement of the transmission output shaft from the teeth on a chopper wheel. The Engine Control Module (ECM) converts the signal from the vehicle speed source into vehicle speed for the following functions:

• Cruise control

• Fast idle

• Idle speed control

• Progressive shift

• Speedometer

• PTO operation

• Vehicle speed limiting

• Idle shutdown

• Operation of the air inlet heater (if equipped)

• Secure idle theft deterrent

• Trip data

• Maintenance data

To begin troubleshooting a vehicle speed problem, the following information must be determined:

The problem is electrical or the problem is a calibration problem.

Electrical problems would be an erratic speed signal or no speed signal. A calibration problem would be a stable ECM speed that is still an inaccurate ECM speed. Another calibration problem would be a stable speedometer speed that is still an inaccurate speedometer speed.

If the problem is related to vehicle speed calibration, refer to Troubleshooting, "Vehicle Speed - Calibrate" for calibrating the vehicle speed in PPKM (pulses per kilometer) or ppm (pulses per mile). The ECM speedometer output signal is set to 18,600 PPKM (30,000 ppm) for most configurations. For "GM Truck Manufacturer" configurations, the output of the speedometer is set to 2,485 PPKM (4,000 ppm). The ECM speedometer output signal cannot be changed. All speedometers that are driven by the ECM output (J1/P1 terminal 36 and terminal 37) must match the fixed output of the ECM for proper operation.

The type of vehicle speed sensor that is installed on the vehicle must be determined.

Both single coil magnetic sensors and dual coil magnetic sensors are commonly used. Some vehicles provide the vehicle speed through the transmission ECM.

You must determine if the vehicle speedometer is driven from the ECM.

The ECM can drive the speedometer through the connection to ECM connector J1-36 (speedometer positive) and/or J1-37 (speedometer negative).

Note: The ECM may also drive the speedometer by a connection to the J1587 ATA Data Link, if the instrument cluster is capable of interpreting the signal.

Vehicle Speed Circuit Wiring

The vehicle speed signal is routed directly into the ECM at ECM vehicle harness connector J1/P1-32 (vehicle speed in positive) and J1/P1-33 (vehicle speed in negative).

Speedometer Connection

If the vehicle speedometer is driven by the ECM output, the vehicle speedometer will be connected to the ECM vehicle harness connector J1/P1-36 and/or to J1/P1-37. Some speedometers require only one of the ECM signal lines to operate. Other speedometers may require both of the ECM signal lines to operate.

Speedometer Special Test

If the vehicle speedometer is driven by ECM output, the speedometer circuit can be checked by using the electronic service tool. The "55 mph VSP/Speedometer Test" will drive the speedometer to approximately 55 mph under the following conditions:

• The "55 mph VSP/Speedometer Test" is activated.

• The circuit is operating properly.

• The speedometer is operating properly.

Note: While the test is active, the odometer will increment mileage.

Magnetic Sensors

A magnetic pickup will have only two wires if the magnetic pickup is a single coil magnetic sensor. Also, a magnetic pickup will have four wires if the magnetic pickup is a dual coil magnetic sensor. The magnetic pickup sensor does not require a power connection or a ground connection.

Vehicles with Electronic Vehicle Speed Sources

For these vehicles, the vehicle speed signal is provided by an electronic source. The signal is received over a single wire that is connected to ECM vehicle harness connector J1/P1-32 (vehicle speed in positive). Do not make any other connection to this line. A speedometer is an example of a connection that should not be made to this line. For this type of signal, the ECM vehicle harness connector J1/P1-33 (vehicle speed in negative) must not be connected to the ECM in order to prevent introducing electrical noise into the circuit.

For vehicle speed problems on trucks that are equipped with either of these vehicle speed sources, first inspect the wiring from the electronic source to the engine ECM for open circuits or for short circuits.

The ECM can be configured to receive vehicle speed information from an electronic transmission control unit via the J1939 data link. The transmission must be capable of supporting the "J1939 ETC1 Broadcast Message (PGN 61,442 Bytes 2 & 3)". This message provides the speed of the transmission output shaft. This feature requires the hardware for the J1939 data link to be installed in the chassis of the vehicle. This also requires a transmission that is electronically controlled and capable of supporting the necessary J1939 protocol.

When the engine is configured for the J1939 option, the circuit for the ECM vehicle speed input (terminals 32 and 33) will be ignored. The ECM uses the "Vehicle Speed Cal (J1939-Trans)" parameter value in order to calculate vehicle speed. The ECM uses the parameter value and the speed of the output shaft that is received over the J1939 data link to calculate the vehicle speed. The "Vehicle Speed Cal (J1939-Trans)" parameter is based on the revolutions per mile of the output shaft. There are several methods that can be used to arrive at this calibration value. Refer to Troubleshooting, "Vehicle Speed - Calibrate" for details.

The ECM can be configured to receive vehicle speed information from the Anti-lock Brake System (ABS) via the J1939 data link. The ABS must be capable of supporting the "J1939 High Resolution Wheel Speed Broadcast Message (PGN 65, 134 Byte 5-8)", which provides wheel speed from the two rear wheels. The ABS will broadcast the assumed tire revolutions per mile.

Regardless of the source that is used to determine vehicle speed, the ECM uses the calculated value for the vehicle speed in the same manner to control several features and functions. The diagnostics for vehicle speed function similarly when either a hard-wired signal is provided to the ECM from a speed sensor, or a message is sent to the ECM via the J1939 data link. If the ECM detects a loss of vehicle speed or a value that is invalid, a fault code will be logged in order to alert the operator or the technician of the presence of a problem.

Illustration 1	g00643046
Schematic for a single coil speed sensor and an ECM driven speedometer

Illustration 2	g00643048
Schematic for a single coil speed sensor and a second single coil sensor for a speedometer

Illustration 3	g00643050
Schematic for a single coil speed sensor and a data link driven speedometer

Illustration 4	g00643051
Schematic for an electronic vehicle speed source and an ECM driven speedometer

Illustration 5	g00643052
Schematic for an electronic vehicle speed source and a speedometer

Illustration 6	g01152556
Pin locations on ECM connector (P1-32) Vehicle speed positive (P1-33) Vehicle speed negative (P1-36) Speedometer positive (P1-37) Speedometer negative

Test Step 1. Inspect Electrical Connectors and Wiring

1. Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector and the terminals for vehicle speed (terminals 32 and 33) in the connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the vehicle speed sensor.

   Refer to Illustration 6.

3. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

4. Check the harness and the wiring for abrasion and for pinch points from the sensor to the ECM.

Expected Result:

All connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion, and of 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. Determine the Type of Vehicle Speed Problem

1. Connect Caterpillar Electronic Technician (ET) to the data link connector.

2. Perform a dynamometer test on the vehicle or perform a road test on the vehicle. Compare the vehicle speed on the Cat ET status screen against the speedometer. Also, compare the vehicle speed on the Cat ET status screen against the actual vehicle speed. The actual vehicle speed can be measured on a dynamometer or the actual vehicle speed can be measured by a stopwatch.

3. Monitor the vehicle speed status on Cat ET while the vehicle is parked and the engine is running.

4. Operate various electrical devices in the vehicle while the vehicle speed is being monitored. In order to operate the various electrical devices, cycle the electrical devices to the ON position and the OFF position.

5. Increase the engine rpm a few times and decrease the engine rpm a few times.

   Note: If the operation of a specific electrical device is producing a vehicle speed problem, the electrical device may be the source of an electrical noise problem. An electrical noise problem is also a possibility if increasing the engine rpm on a stationary vehicle produces a vehicle speed problem.

Expected Result:

Result 1 The speed that is displayed on the Cat ET status screen and the speed of the ECM driven speedometer are stable and both speeds agree with the actual speed.

Result 2 The Cat ET status screen and speed is stable, but incorrect.

Result 3 The Cat ET status screen agrees with the actual speed, but the ECM driven speedometer is incorrect or inoperable.

Result 4 The speed that is displayed on the Cat ET status screen is not present, unstable, or erratic.

Results:

• Result 1 - The readings are correct. There is not a vehicle speed problem at this time. There may be an intermittent problem. Continue troubleshooting until the condition is resolved.STOP

• Result 2 - The Cat ET status screen and speed is stable, but incorrect.

  Repair: Calibrate the vehicle speed circuit. Refer to Troubleshooting, "Vehicle Speed - Calibrate".

  STOP

• Result 3 - The Cat ET status screen agrees with the actual speed, but the ECM driven speedometer is incorrect or inoperable. Proceed to Test Step 3.

• Result 4 - The speed that is displayed on the Cat ET status screen is not present, unstable, or erratic. Proceed to Test Step 4.

Test Step 3. Use Cat ET to Check the Speedometer

Illustration 7	g01152565
Pin locations on ECM connector (P1-32) Vehicle speed positive (P1-33) Vehicle speed negative (P1-36) Speedometer positive (P1-37) Speedometer negative

1. Inspect vehicle harness connector P1. Observe whether connections are present at P1-36 (speedometer positive) and/or at P1-37 (speedometer negative).

   If there is a connection to either of the speedometer terminals continue with the procedure.

2. Access the "55 mph VSP/Speedometer Test" by accessing the following display screens in order:
   • "Diagnostics"

   • "Diagnostic Tests"

   • "Special Test menu"

3. Activate the test and observe the speedometer.

   Note: Some types of speedometers only require one ECM signal line to be connected to the speedometer. Either of the ECM terminals can be used for these speedometers.

   Refer to Illustration 7.

Expected Result:

The speedometer indicates 80 to 96 km/h (50 to 60 mph).

Results:

• OK - The ECM is providing the signal for the speedometer and the wiring and the speed are OK. If an intermittent problem is suspected you may want to send the vehicle to the OEM dealer for repair of the speedometer.STOP

• Not OK - Speed is outside of the range.

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Vehicle Speed - Calibrate"

  STOP

• Not OK - ECM not connected to the speedometer.

  Repair: If OEM truck wiring diagrams are available, trace the wiring to the speedometer and repair the speedometer. You may want to send the vehicle to the OEM dealer for repair.

  STOP

• Not OK - No speed indicated.

  Repair: If OEM truck wiring diagrams are available, trace the wiring to the speedometer and repair the speedometer. You may want to send the vehicle to the OEM dealer for repair.

  STOP

Test Step 4. Determine the Type of Vehicle Speed Circuit

1. Inspect the vehicle wiring for the type of vehicle speed circuit that is being used.

   Compare the vehicle speed circuit with the detailed circuit schematics:

   Schematic 1 Refer to Illustration 1.

   Schematic 2 Refer to Illustration 2.

   Schematic 3 Refer to Illustration 3.

   Schematic 4 Refer to Illustration 4.

   Schematic 5 Refer to Illustration 5.

   Select the schematic that is similar to the circuit that is being repaired.

Expected Result:

RESULT 1 The vehicle speed circuit is similar to schematic 1, 2, or 3.

RESULT 2 The vehicle speed circuit is similar to schematic 4 or 5.

RESULT 3 The ECM is configured for the "J1939 Trans" option.

Results:

• Result 1 - The vehicle speed circuit is similar to schematic 1, 2, or 3. Proceed to Test Step 5.

• Result 2 - The vehicle speed circuit is similar to Schematic 4 or 5. Proceed to Test Step 7.

• Result 3 - The ECM is configured for the "J1939 Trans" option. Proceed to Test Step 9.

Test Step 5. Measure Vehicle Speed Sensor Resistance at the Sensor

1. Disconnect the vehicle speed sensor from the vehicle harness.

2. Thoroughly inspect the connector. Ensure that the connector terminals are free of corrosion and ensure that the connector terminals are fully seated into the housing of the connector. Repair the connector terminals or replace the connector terminals, as required.

3. Measure the resistance between the two terminals of the sensor connector. The sensor resistance measurement should be 100 to 4500 Ohms.

4. Reverse the meter leads and measure the resistance. Switching the probes should not change the resistance measurement by more than ten Ohms.

Expected Result:

The sensor resistance that is measured is between 100 and 4500 Ohms and the sensor resistance that is measured is within ten Ohms with the meter probes in either position.

Results:

• OK - The readings are correct. Connect the sensor to the vehicle harness. Proceed to Test Step 6.

• Not OK - The sensor resistance that is measured is not between 100 and 4500 Ohms or the sensor resistance that is measured is not within ten Ohms with the meter probes in either position.

  Repair: Replace the sensor. Send the vehicle to the OEM dealer for repairs, if necessary.

  STOP

Test Step 6. Inspect the Passive Magnetic Speed Sensor for Vehicle Speed

1. Remove the vehicle speed sensor from the transmission and inspect the vehicle speed sensor for steel shavings, debris, or damage.

   Note: Shavings and debris on the sensor may occur unless the transmission fluid is drained and replaced according to the maintenance schedule.

2. Wipe off the sensor until the sensor is clean. Test the sensor according to the manufacturer's instructions. The sensor is OEM supplied.

   Note: If the gap between the vehicle speed sensor and the chopper wheel is too small, the sensor may be damaged. Also if the gap between the vehicle speed sensor and the chopper wheel is too small, the sensor may create a signal due to the vibration of the chopper wheel. This will cause a vehicle speed signal when the vehicle is parked. If the vehicle is parked and a vehicle speed signal is produced, back out the sensor from the wheel until the signal disappears. Use caution. backing out the sensor too far may cause a loss of the vehicle speed signal. Back out the sensor no more than one turn to one and one quarter turns.

Expected Result:

The vehicle speed sensor is correctly installed and undamaged.

Results:

• OK - The vehicle speed sensor is correctly installed and undamaged. Proceed to Test Step 7.

• Not OK - There is a problem with the vehicle speed sensor.

  Repair: Install the sensor correctly, when possible. Replace parts, if necessary. Send the vehicle to an OEM dealer for repairs, if necessary.

  STOP

Test Step 7. Test ECM Vehicle Speed Inputs by Using the Speedometer Special Test on Cat ET

Illustration 8	g01152566
Jumper wire locations for breakout T (P1-32 to P1-36) Jumper wire (P1-33 to P1-37) Jumper wire

1. Turn the ignition key switch to the OFF/RESET position.

2. Fabricate two jumper wires 100 mm (4 inch) long. Crimp a Deutsch pin to both ends of the wires.

3. Disconnect vehicle harness connector P1 from the ECM.

4. Connect a breakout T to ECM connector J1 and connect P1 to the breakout T.

5. Install one jumper into the breakout T in order to connect terminal 36 (speedometer positive) to terminal 32 (vehicle speed in positive). Install the other jumper into the breakout T in order to connect terminal 37 (speedometer negative) to terminal 33 (vehicle speed in negative).

   Refer to Illustration 8.

6. Turn the ignition key switch to the ON position.

7. Access the "55 mph VSP/Speedometer Test" by accessing the following display screens in order:
   • "Diagnostics"

   • "Diagnostic Tests"

   • "Special Test menu"

8. Activate the test and observe the vehicle speed on the vehicle speed status screen.

Expected Result:

Cat ET indicates a constant vehicle speed between 80 to 96 km/h (50 to 60 mph) when the jumper wires from the speedometer circuit are connected.

Results:

• OK - The ECM is operating correctly. The source of the problem is either the wiring or the source of the problem is the vehicle speed sensor.

  Repair: Perform the following repair:If the sensor is damaged, replace the damaged sensor or send the vehicle to the OEM dealer for repairs.Verify that any repair eliminates the problem.

  STOP

• Not OK - Recheck the connections of the jumper wires. Leave the jumper wires installed in the breakout T. Disconnect the breakout T. Proceed to Test Step 8.

Test Step 8. Test the ECM Vehicle Speed Inputs when the Test ECM is Installed

1. Connect a test ECM and reconnect the breakout T.

2. Install one jumper into the breakout T in order to connect terminal 36 (speedometer positive) to terminal 32 (vehicle speed in positive). Install the other jumper into the breakout T in order to connect terminal 37 (speedometer negative) to terminal 33 (vehicle speed in negative).

   Refer to Illustration 8.

3. Turn the ignition key switch to the ON position.

4. Verify that Cat ET is connected to the data link connector.

5. Access the "55 mph VSP/Speedometer Test" by accessing the following display screens in order:
   • "Diagnostics"

   • "Diagnostic Tests"

   • "Special Test menu"

6. Activate the test and observe the vehicle speed on the vehicle speed status screen.

Expected Result:

Cat ET indicates a constant vehicle speed between 80 to 96 km/h (50 to 60 mph) when the jumper wires from the speedometer circuit are connected.

Results:

• Yes - The indication is correct.

  Repair: Connect the original ECM. If the problem returns with the original ECM, replace the ECM.

  STOP

• No - The indication is not correct. There may be an intermittent problem. Recheck the connectors. Continue troubleshooting until original condition is resolved.STOP

Test Step 9. Verify Correct Programming for the "J1939 Vehicle Speed Calibration" Parameter

1. Access the list of "Configuration Parameters" on Cat ET and verify that the "Vehicle Speed Input" parameter is programmed to the "J1939 Trans" option.

2. Verify that the "Powertrain Datalink" parameter is programmed to "J1939".

3. Verify that the correct value is used for the "Vehicle Speed Cal (J1939-Trans)" parameter. Refer to Troubleshooting, "Vehicle Speed - Calibrate" for details.

4. Verify that the J1939 data link is connected to the ECM and that the data link is functioning properly. Refer to Troubleshooting, "Data Link - Test".

5. Compare the vehicle speed reading on the Cat ET status screen to the vehicle speedometer and the actual vehicle speed.

Expected Result:

The "Vehicle Speed" on the Cat ET status screen is within 8 km/h (5 mph) of the speedometer and the actual vehicle speed readings.

Results:

• Yes - The indication is correct. The ECM is receiving J1939 data from the transmission ECM. Send the vehicle to the OEM dealer for repair of the wiring for the speedometer or for the repair of the vehicle speed sensor for the transmission. STOP

• No - The indication is not correct.

  Repair: Connect a test ECM. Program all of the parameters that are related to vehicle speed to the same setting as the original ECM. Repeat the previous test step. If the test ECM functions properly and the original ECM does not function properly, replace the ECM. If the test ECM does not correct the problem, send the vehicle to an OEM dealer for repair of one of the following components:

  • Speedometer

  • Wiring

  • Transmission ECU

  • Transmission speed sensor

  • Wiring for the J1939 data link

  STOP