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U183C




DTC U183C

Diagnostic Instructions

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

DTC Descriptor
DTC U183C 00
- Auxiliary Transmission Fluid Pump Lost Communication with Hybrid Powertrain Control Module 2 on Powertrain Expansion Communication Bus

Diagnostic Fault Information






Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. When the vehicle is ON, each control module communicating on the serial data circuit sends a state of health (SOH) message to ensure that the control module is operating properly. When hybrid powertrain control module 2 stops communicating on the serial data circuit, for example if the hybrid powertrain control module 2 loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the loss of SOH of the hybrid powertrain control module 2. A loss of serial data communications DTC does not represent a failure of the control modules that contain the stored code.

The auxiliary transmission fluid pump control module is controlled by drive motor 3 control module. The communication for auxiliary transmission fluid pump control module and all drive motor control modules is handled through the hybrid powertrain control module 1. The auxiliary transmission fluid pump control module and the hybrid powertrain control module 1 are all internal to the power inverter module. All circuits to the auxiliary transmission fluid pump control module and hybrid powertrain control module 1 are also internal to the power inverter module. Communication diagnostics for the serial data, including control module power and ground as well as the wakeup circuits, for auxiliary transmission fluid pump control module and the hybrid powertrain control module 1 are all diagnosed from external sources only to the power inverter module connector.

Conditions for Running the DTC

The system voltage is at least 10 V.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

The DTC U183C is a type B DTC.

Conditions for Clearing the DTC

The DTC U183C is a type B DTC.

Diagnostic Aids

* 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 control module on the data communication circuit was disconnected while the communication circuit is awake.
- Power to one or more control modules was interrupted during diagnosis.
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
- Battery power was restored to the vehicle and control modules 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 control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.
* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
* Communication may be available between the control module and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the control module using multiple GMLAN busses.
* Use Data Link References Initial Inspection and Diagnostic Overview to determine what GMLAN serial data communications the non communicating control module uses.
* The control module 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 control module.

Reference Information
Schematic Reference

* Data Communication Schematics [1][2]Electrical Diagrams
* Control Module References Programming and Relearning

Connector End View Reference

Component Connector End Views Hybrid/EV Battery Pack X1
Description and Operation

Data Link Communications Description and Operation Description and Operation
Electrical Information Reference

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

Scan Tool Reference

Control Module References Programming and Relearning for scan tool information

Circuit/System Verification

Verify that DTC U0074, U1814, U2099, B1428, B1370, B1380, B1440, B1441, B1325, or P0562 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

Circuit/System Testing

Note: Use the schematic to identify the following:

* The control module location on the powertrain high speed GMLAN serial data circuits
* The control module B+, ignition, ground, accessory wake up serial data and serial data circuit terminals

1. Vehicle OFF, disconnect the harness connector at the K114B hybrid powertrain control module 2.
2. Test for less than 10 ohm between each ground circuit terminal and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. If equipped, vehicle in Service Mode, verify that a test lamp illuminates between each B+ circuit terminal and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the K114B hybrid powertrain control module 2 for a short to ground. If the circuits test normal, replace the K114B hybrid powertrain control module 2.

4. If equipped, vehicle in Service Mode, verify that a test lamp illuminates between each ignition circuit terminal and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the K114B hybrid powertrain control module 2 for a short to ground. If the circuits test normal, replace the K114B hybrid powertrain control module 2.

5. If equipped, vehicle in Service Mode, verify that a test lamp illuminates between the accessory wake up serial data circuit terminal and ground.

• If the test lamp does not illuminate, test the entire circuit, including the B+ circuit to the K9 body control module (BCM), for an open/high resistance or a short to ground. If the circuits test normal, replace the K9 BCM.

6. Vehicle OFF, disconnect the X1 harness connector at the T6 power inverter module.
7. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 2 ohm in each powertrain high speed GMLAN serial data circuit between the K114B hybrid powertrain control module 2 and the T6 power inverter module.

• If greater than the specified range, test the serial data circuit for an open/high resistance between the K114B hybrid powertrain control module 2 and the T6 power inverter module.

8. If all circuits test normal, replace the K114B hybrid powertrain control module 2.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Control Module References Programming and Relearning for control module replacement, programming and setup

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