Bulletin No.:

Service Bulletin

Date:

20-NA-198
October, 2020

TECHNICAL
Subject:

Trailer Running Lights Shut Off Due to Excessive Load on the Running Lamp Circuit

Brand:

Model:

Chevrolet

Silverado 1500
(New Model)

GMC

Sierra 1500
(New Model)

Model Year:
from

to

2019

2019

VIN:
from

Engine:

Transmission:

All

All

to

Involved Region or Country

North America, Middle East, Argentina (Mercosur), Brazil (Mercosur), Bolivia (West),
Chile (West), Colombia (West), Ecuador (West), Paraguay (West), Peru (West), Uruguay
(West), GM Korea Company, Singapore, Phiippines, Egypt, Other Africa, South Africa.

Additional Options (RPOs)

Equipped with INDICATOR-TRAILER INFORMATION (U1D)

Condition

Some customers may comment that the running lamps may illuminate for a second or
two, and then go out when operating a trailer running lamp circuit with more than 7-8
amps of current draw. On vehicles with LED lighting, the owner may have concerns with a
flash of the lighting about once every 10 seconds.

Cause

The cause of the condition may be that trailers with incandescent running lamps may
have in-rush current that exceeds the trailer lighting module limits for current flow. And
that monitoring voltage may illuminate LED lights even when trailer theft deterrent is not
enabled.

Additional Information

2019 Model Year vehicles, equipped with U1D, use the K68 Trailer Lighting Control
Module to control all trailer lighting through pulse width modulated (PWM) voltage. The
Trailer Lamp Control Module has a current handling capability on the running lamp circuit
of about 9 amps. On a trailer with a large number of incandescent lights, in-rush current
can exceed 20 amps before it settles back to around 8-9 amps. During this inrush or
"marriage" current period, the Trailer Lamp Control Module sees the current as an
"overload" and goes into protection mode.
This was changed for MY 20 to allow 16 amps of continuous current flow by routing the
current through an internal relay in the Trailer Lamp Control Module. 2019 Trucks can be
modified to operate in the same way. If we use 2020 design software and re-pin the
running lamps to pin 25 using the internal relay to operate the running lamps. This
requires a terminated lead to be inserted into cavity 25 on the chassis harness X1
connector. Wiring connected to pin 5 on the X1 will be cut and reconnected to Pin 25.
Terminal in cavity 5 will remain, be blunt cut, and sealed with a closed end duraseal splice
to prevent water entering through pin 5.
Software will have to be managed by TCSC. A record must exist of what trucks have
been flashed and that the bulletin has been completed. Software will not work with the
production configuration of wiring. This also changes the trailer connection detection
flashing of LED lighting from every 10 seconds to every 42 minutes. (Connection
detection will still be enabled if trailer theft deterrent is enabled).

Copyright 2020 General Motors LLC. All Rights Reserved.

Page 2

October, 2020

Bulletin No.: 20-NA-198

Correction

5652571

Following the steps in the Service Procedure below, move circuit 2109 on the railer Lamp
Control Module from X1 cavity 5 to X1 cavity 25, and load new software from SPS into the
Trailer Lamp Control Module.

Service Procedure
1. Raise and support the vehicle. Refer to Lifting and
Jacking the Vehicle in SI.
2. Lower and reposition the spare tire, if necessary.

Bulletin No.: 20-NA-198

October, 2020

Page 3

5209978

3. Locate the Trailer Lamp Control Module (2) and
disconnect the chassis harness X1 electrical
connector.

5652574

5652572

4. Cut off the tie strap retaining the wiring harness
and remove the cover from the connector.

5. Pull the wiring harness out of protective sleeve,
and trim back previous tape to access the wiring.

Page 4

October, 2020

5652575

Bulletin No.: 20-NA-198

5652578

7. Release the 4 tabs on the Terminal Position
Assurance (TPA) and pull slightly upward to
partially release it from the connector housing.

5652576

6. Locate the Gray/Brown wire, at pointer (1),
connected to cavity 5, and cut the wire
approximately 7.62 cm (3.0 in) from the connector
body. The wire will be re-located to cavity 25 (2).

5662018

Bulletin No.: 20-NA-198

October, 2020

5652580

8. Remove the seal from connector cavity 25 and
install the new terminated lead (1) into this cavity.
Ensure the terminal locks into place by pulling back
gently on the wire.

Page 5

5662021

10. Crimp a salmon Duraseal splice sleeve onto the
striped end of the wire stub in cavity 5 of the
connector. Attach the harness side of the grey
brown wire to the end of the terminated lead that
was just installed into cavity 25, using another
salmon duraseal splice sleeve.

5652578

9. Gently press down on the TPA until all 4 tabs
re-engage with the connector and are fully seated.

5662022

11. Use the Ultra torch to shrink the spice sleeve
around the wire and also seal the open end. Use
the Ultra torch to shrink the splice sleeve around
the grey/brown and white terminated lead wires.
Refer to the Weatherpack™ Wiring Repair section
of Wire to Wire Repair. in SI.

Page 6

October, 2020

Bulletin No.: 20-NA-198

13. Reinstall the connector cover and reconnect the
connector. Replace the tie strap that was removed
previously.
14. Remove the support and lower the vehicle.
15. After installation, contact TCSC to obtain the
correct software update and reprogram the Trailer
Lamp Control Module. Refer to, K68 Trailer
Lighting Control Module: Programming and Setup,
in SI.

Parts Information
Causal
Part

N/A

5652583

12. Using Woven Polyester (PET) Electrical/
Anti-Abrasive Tape, or equivalent, re-tape the
harness where the previous tape was removed and
reposition the harness back inside the sleeve.

Description

Part
Number

Qty

WIRE,SPLICE
(TERMINATED
LEAD)

13575368

1

SPLICE,WIRE
(SALMON)

19300089

2

Warranty Information
For vehicles repaired under the Bumper-to-Bumper
coverage (Canada Base Warranty coverage), use the
following labor operation. Reference the Applicable
Warranties section of Investigate Vehicle History (IVH)
for coverage information.

Labor Operation

Description

Labor Time

5480858*

Move Circuit 2109 on the Trailer Lamp Control Module, and
Load New Software from SPS

1.0 hr.

*This is a unique Labor Operation for Bulletin use only.

Version

2

Modified

Released September 28, 2020
Revised October 23, 2020 – Revised Text in Several Procedure Steps to Better Clarify
Repair, Added Graphic, Updated Parts Information

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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TECHNICIAN
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