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.

Bulletin No.: 20-NA-198

October, 2020

Page 3

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.

5209978

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

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

5652574
5652572

Page 4

October, 2020

Bulletin No.: 20-NA-198

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

5652578

5652575

7. Release the 4 tabs on the connector body 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).

5652580

8. Push the terminated lead (1) from the new white
wire splice into cavity 25.

Bulletin No.: 20-NA-198

October, 2020

Page 5

10. Heat shrink, referencing Wire to Wire Repair. in SI.

5652581

9. Cap the previously cut Gray/Brown wire and seal
with a closed end duraseal splice. Take the open
end of the white wire, add a duraseal and connect
to open cut end of the Gray/Brown wire.

5652583

11. 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.
12. Reinstall the connector cover and reconnect the
connector. Replace the tie strap that was removed
previously.
13. Remove the support and lower the vehicle.
14. After installation, reprogram the Trailer Lamp
Control Module. Refer to, K68 Trailer Lighting
Control Module: Programming and Setup, in SI.

Parts Information
Causal
Part

Description

Part
Number

Qty

N/A

WIRE,SPLICE

13575368

1

Warranty Information

5652582

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

1

Modified

Released September 28, 2020

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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