File in Section:

Service Bulletin

-

Bulletin No.:

18-NA-096

Date:

April, 2018

TECHNICAL
Subject:

MIL ON – DTC U016B Lost Communication with Electric A/C Compressor Control
Module Set and Will Not Clear

Brand:

Model:

Cadillac
Chevrolet

Model Year:

VIN:

Engine:

Transmission:

—

2.0L (RPO
LTG) (Plug-In)

—

—

1.5L (RPO L3A)
(Hybrid)

—

from

to

from

to

CT6

2017

2018

—

Volt D2

2017

2018

—

Involved Region or Country

United States, Canada, Korea

Condition

The Technician may notice that the Malfunction Indicator Lamp (MIL) is illuminated after
servicing the vehicle.

Cause

The Technician may find DTC U016B Lost Communication with Electric A/C compressor
Control Module set. This occurs when the device is disconnected while the
communication circuit is still awake.

Correction

Allow the vehicle to power down for three to five minutes and then disconnect the Battery
Negative Cable for approximately three minutes.

•

Service Recommendation
•
Information Why Communication U Code is Present
Sometimes, while diagnosing a specific customer
concern or after a repair, the Technician 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
the following 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.

Copyright 2018 General Motors LLC. All Rights Reserved.

Battery power was restored to the vehicle and the
devices on the communication circuit did not all
re-initialize at the same time.
If a Lost 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.

Clearing the Communication U Code
1. Ignition ON/Vehicle in Service Mode.
2. Perform the Diagnostic System Check - Vehicle.
3. Verify that DTC U016B is set.
⇒ If only DTC U016B is set Go to Step 4.
⇒ If any other DTCs are set, refer to Diagnostic
Trouble Code (DTC) List - Vehicle in SI.
4. Allow the vehicle to power down for three to five
minutes and then disconnect the Battery Negative
Cable for approximately three minutes. Refer to
Battery Negative Cable Replacement in SI.
5. Connect the Battery Negative Cable.
6. Using the scan tool confirm that the Air Conditioner
Compressor Control Module is communicating.
7. Perform the Diagnostic Repair Verification after
completing the repair. Refer to Diagnostic Repair
Verification in SI.

Page 2

April, 2018

Bulletin No.: 18-NA-096

Parts Information
No parts are required for this repair.

Version Information
Version

1

Modified

Released March 29, 2018

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a
job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.

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