U184F
DTC U184F
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 U184F 00
- Electric A/C Compressor Control Module Lost Communication with Engine Control Module
Diagnostic Fault Information
Circuit/System Description
Control modules connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the control modules. The control modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
Conditions for Running the DTC
* The system voltage is between 9-16 volts.
* The vehicle power mode master requires serial data communication to occur from this specific control module.
* No "bus off" condition is present.
Conditions for Setting the DTC
The A/C compressor is not able to receive the serial data message from the engine control module for 3 seconds.
Action Taken When the DTC Sets
The control module is never signaled. Therefore, the specific subsystems will not function.
Conditions for Clearing the DTC
The DTC clears when the A/C compressor receives the serial data message from the engine control module.
Diagnostic Aids
Different DTCs may set in different control modules along with this DTC depending on where the fault occurs and the vehicle operating conditions when the fault occurs.
Reference Information
Schematic Reference
* Data Communication Schematics [1][2]Electrical Diagrams
* Control Module References Control Module References
Connector End View Reference
Component Connector End Views Hybrid/EV Battery Pack X1 A4
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 Control Module References for scan tool information
Special Tools
EL-48900 - HEV Safety Kit
Circuit/System Verification
1. Verify that DTC U0100 is not set.
• If the DTC is set, refer to DTC U0100-U02FF U0100.
2. Verify that DTC U0073, P06E4, U1814, U2099, B1428, B1370, B1380, B1440, B1441, B1325, or P0562 is not set.
• If any of these DTCs is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
Circuit/System Testing
Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.
The High Voltage Disabling procedure will perform the following tasks:
* Identify how to disable high voltage.
* Identify how to test for the presence of high voltage.
* Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:
* Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors.
* Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.
- Visually and functionally inspect the gloves before use.
- Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.
Failure to follow the procedures exactly as written may result in serious injury or death.
Note: Use the schematic to identify the following:
* Control module location on the high speed GMLAN serial data circuits
* The control module B+, ignition, ground, communication enable and serial data circuit terminals
1. Ignition OFF, disconnect harness connector at the K20 engine control module (ECM).
2. Test for less than 10 ohm between each ground circuit terminal and ground.
• If greater than the specified value, test the ground circuit for an open/high resistance.
3. If equipped, ignition ON, 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 K20 ECM for a short to ground. If the circuits test normal, replace the K20 ECM.
4. If equipped, ignition ON, 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 K20 ECM for a short to ground. If the circuits test normal, replace the K20 ECM.
5. If equipped, ignition ON, verify that a test lamp illuminates between the wake-up circuit terminal and ground.
• If the test lamp does not illuminate, test the entire circuit, including the B+ circuit to the K114B hybrid powertrain control module 2, for an open/high resistance or short to ground. If the circuits test normal, replace the K114B hybrid powertrain control module 2.
6. Ignition OFF, disable the high voltage system. Refer to High Voltage Disabling High Voltage Disabling.
7. Reconnect the 12 V battery.
8. Ignition OFF, disconnect harness connector at the G1 A/C compressor.
9. Ignition 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 1 ohm in each high speed GMLAN serial data circuit between the K20 ECM and the G1 A/C compressor:
• If greater than the specified range, test the serial data circuit for an open/high resistance between the K20 ECM and the A/C compressor.
10. If all circuits test normal, replace the K20 ECM.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Control Module References Control Module References for control module replacement, programming and setup