Trailer Running Lights Shut Off Due to Excessive Load on the Running Lamp Circuit – 2019-2020 Chevrolet Silverado & GMC Sierra

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Service Bulletin Bulletin No.: 20-NA-198
Date: December, 2020
TECHNICAL
Subject: Trailer Running Lights Shut Off Due to Excessive Load on the Running Lamp Circuit
Brand: Model:
Model Year: Date Breakpoint: Engine: Transmission:
from to from to
Chevrolet
Silverado 1500
(New Model) 2019 2019
All All
Silverado 1500
Silverado 2500HD/ 2020 2020
3500HD
GMC
Sierra 1500
(New Model) 2019 2019
Sierra 1500
Sierra 2500HD/ 2020 2020
3500HD
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).
Page 2 December, 2020 Bulletin No.: 20-NA-198
Correction
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For 2019 models ONLY, Follow the steps in the Service Procedure below, and move
circuit 2109 on the Trailer Lamp Control Module from X1 cavity 5 to X1 cavity 25, and load
new software from SPS into the Trailer Lamp Control Module.
For 2020 models ONLY, no wiring changes are required. Only the software update from
SPS to change the monitoring of the trailer lamps from once every 10 seconds to once
every 42 minutes, will have to be completed.
Service Procedure
Important:
• For 2019 models ONLY, the complete
Service Procedure must be completed.
• For 2020 models ONLY, jump ahead to step
#15 and complete the software update, and
reprogramming, only.
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 December, 2020 Page 3
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3. Locate the Trailer Lamp Control Module (2) and
disconnect the chassis harness X1 electrical
connector.
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4. Cut off the tie strap retaining the wiring harness
and remove the cover from the connector.
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5. Pull the wiring harness out of protective sleeve,
and trim back previous tape to access the wiring.
Page 4 December, 2020 Bulletin No.: 20-NA-198
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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).
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7. Release the 4 tabs on the Terminal Position
Assurance (TPA) and pull slightly upward to
partially release it from the connector housing.
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Bulletin No.: 20-NA-198 December, 2020 Page 5
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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.
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9. Gently press down on the TPA until all 4 tabs
re-engage with the connector and are fully seated.
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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.
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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 December, 2020 Bulletin No.: 20-NA-198
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.
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
Description Part
Number
Qty
N/A
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* Load New Software from SPS, K68 Trailer Lighting Control
Module Reprogramming 0.3 hr.
Add Move Circuit 2109 on the Trailer Lamp Control Module
(2019 Models Only) 0.7 hr
*This is a unique Labor Operation for Bulletin use only.
Version 3
Modified Released September 28, 2020
Revised October 23, 2020 – Revised Text in Several Procedure Steps to Better Clarify
Repair, Added Graphic, Updated Parts Information
Revised December 04, 2020 – Added 2020 Model Year and Updated Labor Operation
with Add,

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