• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The devices connected to the powertrain high speed CAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices when the ignition switch is in any position other than OFF. The powertrain high speed CAN serial data bus uses terminating resistors that are in parallel with the powertrain high speed CAN (+) and (−) circuits.

• The system voltage is between 9–16 V.
• The vehicle power mode requires serial data communications.

A supervised periodic message that includes the transmitter device availability has not been received for more than 450 ms.

DTC U0074 is a type B DTC.

DTC U0074 is a type B DTC.

• Use the Data Link References to identify the powertrain high speed CAN devices.
• Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated “current” or “active” status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
• A device on the data communication circuit was disconnected while the communication circuit is awake.
• Power to one or more devices was interrupted during diagnosis.
• A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.
• Battery power was restored to the vehicle and devices on the communication circuit did not all re-initialize at the same time.
• If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
• Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
• Communication may be available between some devices and the scan tool with the powertrain high speed CAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
• An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle.
• Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC).
• Some devices may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no device output voltage circuit is shorted to ground before replacing the device.

• Data Communication Schematics
• Control Module References

Master Electrical Component List

Data Link Communications Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Control Module References for scan tool information

1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors with the powertrain high speed CAN serial data circuits at an easily accessible device that is not communicating. It may take up to 2 minutes for all vehicle systems to power down. Refer to Data Link References to determine which devices are on the powertrain expansion bus.
2. Ignition ON.
3. Test for less than 4.5 V between each powertrain high speed CAN serial data circuit at the device that was just disconnected and ground.
• If 4.5 V or greater

  Refer to Testing the Serial Data Circuits for a Short to Voltage.

• If less than 4.5 V
4. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
5. Test for greater than 100 Ω between each powertrain high speed CAN serial data circuit at the device that was just disconnected and ground.
• If 100 Ω or less

  Refer to Testing the Serial Data Circuits for a Short to Ground.

• If greater than 100 Ω
6. Test for 110–130 Ω between each pair of the powertrain high speed CAN serial data circuits at the device that was just disconnected:
• If less than 110 Ω

  Refer to Testing the Serial Data Circuits for a Short between the Circuits.

• If greater than 130 Ω

  Refer to Testing the Serial Data Circuits for an Open/High Resistance.

• If between 110–130 Ω
7. Refer to Testing the Device Circuits.

1. Ignition OFF, disconnect the harness connectors with the powertrain high speed CAN serial data circuits at another device, in the direction of the circuit shorted to voltage, ignition ON.
2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground.
• If each serial data circuit is 4.5 V or less
1. Ignition OFF.
2. Test for less than 10 Ω between each of the device's ground circuit terminals and ground.
• If 10 Ω or greater, repair the open/high resistance in the circuit.
• If less than 10 Ω, replace the device that was disconnected.
• If any serial data circuit is greater than 4.5 V
3. Repeat step 1 until one of the following conditions are isolated:
• A short to voltage on the serial data circuit between two devices or splice packs, if equipped.
• A short to voltage on the serial data circuit between a device and a terminating resistor.

1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
2. Disconnect the harness connectors with the powertrain high speed CAN serial data circuits at another device, in the direction of the circuit shorted to ground.
3. Test for greater than 100 Ω between each serial data circuit at the device connector that was just disconnected and ground.
• If each serial data circuit is 100 Ω or greater

  Replace the device that was disconnected.

• If any serial data circuit is less than 100 Ω
4. Repeat step 1 until one of the following conditions are isolated:
• A short to ground on the serial data circuit between two devices or splice packs, if equipped.
• A short to ground on the serial data circuit between a device and a terminating resistor.

1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
2. Connect the harness connectors at the device that was previously disconnected.
3. Disconnect the harness connectors with the powertrain high speed CAN serial data circuits at another device, in the direction of the circuit shorted together.
4. Test for greater than 110 Ω between each pair of serial data circuits at the device connector that was just disconnected.
• If each pair of serial data circuits is 110 Ω or greater

  Replace the device that was disconnected.

• If any pair of serial data circuits is less than 110 Ω
5. Repeat step 1 until one of the following conditions are isolated:
• Serial data circuits shorted together between two devices or splice packs, if equipped.
• Serial data circuits shorted together between a device and a terminating resistor.
• A shorted terminating resistor.

1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
2. Connect the harness connectors at the device that was previously disconnected.
3. Disconnect the harness connectors with the powertrain high speed CAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.
4. Test for less than 130 Ω between each pair of the serial data circuits at the device connector that was just disconnected.
• If each pair of serial data circuits is 130 Ω or less

  Replace the device that was disconnected.

• If any pair of serial data circuits is greater than 130 Ω
5. Repeat step 1 until one of the following conditions are isolated:
• An open/high resistance on the serial data circuit between two devices or splice packs, if equipped.
• An open/high resistance on the serial data circuit between a device and a terminating resistor.
• An open/high resistance terminating resistor.

1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 Ω between each ground circuit terminal at the device that was just disconnected and ground.
• If 10 Ω or greater
1. Ignition OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, repair the open/high resistance in the ground connection.
• If less than 10 Ω
3. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 Ω in the B+ circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the disconnected device.
• If the test lamp illuminates
4. Ignition ON.
5. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 Ω in the ignition circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the ignition circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the disconnected device.
• If the test lamp illuminates
6. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground.
• If the test lamp does not illuminate
1. Ignition OFF, disconnect the harness connectors at the control module that controls the ignition circuit.
2. Test for infinite resistance between the ignition circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 Ω in the ignition circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the control module that controls the ignition circuit.
• If the test lamp illuminates
7. Replace the device that was disconnected.

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup