• 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.

For symptom byte information, refer to Symptom Byte List.

The Local Interconnect Network (LIN) Bus consists of a single wire with a transmission rate of 10.417 Kbit/s. The serial data is transmitted over a LIN circuit between a master control module and other LIN devices within a particular subsystem. If serial data communication is lost between any of the LIN devices on the LIN bus network, the master control module will set a no communication code against the non-communicating LIN device.

The system voltage is between 9–16 V.

A supervised periodic message that includes the transmitter device availability has not been received.

Specific subsystems will not function.

• A current DTC clears when the malfunction is no longer present.
• A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

• 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.
• A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.
• Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.
• Some devices may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the device.
• An open in the LIN bus serial data circuit between the splice pack and a LIN device will only affect that specific LIN device. This type of failure will set a loss of communication DTC for each LIN device affected and the other LIN devices will still communicate.

• 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

Control Module References for scan tool information

1. Ignition ON/Vehicle In Service Mode.
2. Verify that DTC B1325, B1330, B1370, B1380, B1424, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, P0562, P06E4, U0028, U0029, U0073–U0078, U007A–U007D, U0100–U02FF, U1814, U2098, or U2099 is not set.
• If any of the DTCs are set

  Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

• If none of the DTCs are set
3. Refer to Circuit/System Testing.

1. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the B110 Battery Sensor Module. It may take up to 10 min for all vehicle systems to power down.
2. Test for less than 10 Ω between each ground circuit terminal and ground.
• If 10 Ω or greater
1. Ignition/Vehicle 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. Ignition ON/Vehicle In Service Mode.
4. 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/Vehicle OFF, remove the test lamp.
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/Vehicle OFF, remove the test lamp.
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 B110 Battery Sensor Module.
• If the test lamp illuminates
5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition/Vehicle OFF, remove the test lamp.
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/Vehicle OFF, remove the test lamp.
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 B110 Battery Sensor Module.
• 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/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the control module that controls the ignition circuit and all devices that share the same 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
4. Reconnect the control module that controls the ignition circuit, ignition ON/Vehicle In Service Mode.
5. Verify a test lamp illuminates between the ignition circuit terminal and ground.
• If the test lamp does not illuminate, replace the control module that controls the ignition circuit.
• If the test lamp illuminates
6. Ignition/Vehicle OFF, reconnect the first device that shares the same ignition circuit, ignition ON/Vehicle In Service Mode.
7. Verify a test lamp illuminates between the ignition circuit terminal and ground.
• If the test lamp does not illuminate, replace the device that was just connected.
• If the test lamp illuminates and there are more devices to connect, connect the next device and repeat step 6.7 until there are no more devices to connect.
• If the test lamp illuminates
7. Ignition/Vehicle OFF, disconnect all LIN devices that share the same LIN serial data circuit, ignition ON/Vehicle In Service Mode.

Note: For accurate voltage reading, disconnect the battery charger prior to performing the following test step.

8. Test for 2–12 V between the LIN serial data circuit terminal and ground.
• If less than 2 V
1. Ignition/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the serial data 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 serial data circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω
4. Reconnect the K20 Engine Control Module, ignition ON/Vehicle In Service Mode.
5. Test for 2–12 V between the LIN serial data circuit terminal and ground.
• If less than 2 V, replace the K20 Engine Control Module.
• If greater than 2 V, replace the LIN device that causes a current DTC to set when connected.
• If greater than 12 V
1. Ignition/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON/Vehicle In Service Mode.
2. Test for less than 1 V between the serial data circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Ignition/Vehicle OFF, reconnect the K20 Engine Control Module, ignition ON/Vehicle In Service Mode.
4. Test for 2–12 V between the LIN serial data circuit terminal and ground.
• If greater than 12 V, replace the K20 Engine Control Module.
• If less than 12 V, replace the LIN device that causes a current DTC to set when connected.
• If between 2–12 V
9. Ignition/Vehicle OFF, inspect both harness and component connectors for contamination, corrosion, and terminal tension.
10. Reconnect the harness connectors at the B110 Battery Sensor Module. Verify all connectors/terminals are fully seated.
11. Ignition ON/Vehicle In Service Mode.
12. Verify DTC U01B0 is not set again.
• If the DTC is set

  Replace the B110 Battery Sensor Module.

• If the DTC is not set
13. A fault is currently not present and may be an intermittent condition.

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup