B2699 on 2015-2019 GMC Sierra Denali: Right Headlamp Circuit Fault Causes and Fixes

What's Unique About the 2015-2019 Gmc SIERRA DENALI

The K2XX generation of the GMC Sierra has a sophisticated Body Control Module (BCM) that is highly sensitive to the electrical loads of aftermarket accessories. This code is uniquely and strongly associated with snowplow installations. GM has issued multiple Technical Service Bulletins (TSBs) confirming that when B2699 appears, the root cause is almost always an issue with the snowplow's headlight changeover module, which the BCM misinterprets as a short circuit. 🎬 Watch: How BCM-controlled headlight wiring diagrams work. GM Upfitter Bulletin #116 explains that the BCM performs a diagnostic check when the low beams are commanded on; if an aftermarket module switches power *after* this check, the BCM sees the current inrush as a fault and disables the circuit.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Right low-beam headlight is inoperative.
• Headlights (either truck or plow) flicker or fail to work when switching between them.
• A "Service Headlamp System" message may appear on the driver information center.
• Plow headlights are inoperative after switching from the factory headlights.

Most Likely Causes

1. Improperly Installed or Faulty Snowplow Headlight Wiring/Module 🔴 High Probability As documented in multiple GM TSBs (including PIT5412D), the BCM is sensitive to the delayed current draw from aftermarket headlight switching modules, interpreting it as a short to ground. This is a well-known issue on K2XX trucks with plows.
   How to confirm: Disconnect the snowplow's main electrical harness from the truck. Clear the DTCs with a scan tool. If code B2699 does not return after cycling the ignition and headlights, the fault is definitively in the snowplow's electrical system.
   Typical fix: Contact the snowplow manufacturer for an updated, compatible headlight changeover module or wiring harness. For Western, Fisher, SnowEx, and Blizzard plows, the specific fix for 2015-2019 GM 2500/3500 trucks is the Plug-In Harness Kit P/N 69818-2. This kit is designed to work with the GM BCM logic. Other solutions include using a 'soft start' isolation module like the Fisher/Western 29760-2.
   Est. part cost: $50-$350
2. Damaged Headlight Wiring Harness ⚪ Low Probability
   How to confirm: With the headlight disconnected, use a multimeter to test the control circuit wire between the BCM and the headlight connector for a short to ground. A reading of less than infinite resistance indicates a short.
   Typical fix: Repair the damaged section of the wiring harness and protect it from future damage.
   Est. part cost: $10-$100
3. Faulty Headlight Bulb or Assembly ⚪ Low Probability
   How to confirm: An internally shorted bulb can cause this code, although it's less common than an open circuit from a blown filament. Swap the right and left bulbs to see if the code follows the bulb. A simple burned-out bulb more often sets an 'open circuit' code like B2699 04.
   Typical fix: Replace the headlight bulb. The standard low-beam bulb is type 9012 (HIR2).
   Est. part cost: $20-$50

Rare But Worth Checking

• Faulty Body Control Module (BCM): This is a rare failure. The BCM should only be considered after all other possibilities, especially aftermarket wiring, have been exhaustively ruled out. BCM replacement requires programming by a dealer or qualified shop.

Diagnosis Steps

1. Scan the Body Control Module (BCM) for codes and confirm B2699 is present, noting any other codes like B2575.
2. If a snowplow is installed, this is the primary suspect. Disconnect the main electrical harness for the snowplow from the truck.
3. Clear the DTCs using a scan tool. Cycle the ignition and turn the headlights on.
4. If the code does not return, the fault is in the snowplow's wiring or headlight changeover module. Contact the snowplow manufacturer for support, referencing GM Upfitter Bulletin #116. For many plow brands, the solution is a specific harness kit like Western/Fisher P/N 69818-2.
5. If the code returns with the plow disconnected, inspect the factory headlight wiring harness for any signs of chafing, melting, or corrosion between the BCM and the right headlight.
6. Disconnect the right headlight connector. Use a multimeter to check for a short to ground on the control circuit pin.
7. If no wiring faults are found, test the headlight assembly itself for an internal short by swapping it with the left side assembly if possible.
8. If all wiring and components test good, the BCM may be faulty, which requires advanced diagnostics.

Parts You'll Likely Need

• Snowplow Headlight Harness/Module Kit (OEM #69818-2 (for Western/Fisher/SnowEx/Blizzard)) — This is the most common cause of B2699 on these trucks. The original module from the plow manufacturer is often not compatible with the BCM's circuit protection logic. This specific kit is designed for 2015-2019 GM 2500/3500 trucks.
  Trusted brands: Western, Fisher, BOSS, SnowEx
  OEM price range: $150-$350
• Headlight Bulb (OEM #9012 (HIR2)) — A standard wear item that can, in rare cases, short internally and cause this code.
  Trusted brands: ACDelco, Sylvania, Philips
  OEM price range: $30-$50
  Aftermarket price range: $20-$40
• Soft Start Isolation Module (OEM #29760-2 (for Western/Fisher)) — An alternative solution that provides a 'soft start' for the plow lights, preventing the BCM from detecting a fault. It can be used as an upgrade or replacement for older modules.
  Trusted brands: Western, Fisher
  OEM price range: $125-$195

Related Codes That Often Appear With This One

• B2575 — This code indicates the same fault condition (short/open circuit) but for the left headlamp control circuit. They often appear together when a snowplow system is at fault.

Technical Service Bulletins (TSBs) & Recalls

• PIT5412D: Headlight Flicker or Inoperative When Switching Between The Truck and Snow Plow Headlights.
• PIT5412A: Snow plow headlamps inoperative after switching from the factory headlamps.
• GM Upfitter Bulletin #116: Explains the electrical incompatibility between some aftermarket modules and the BCM's diagnostic routine.
• GM Upfitter Bulletin #124: Details a fix for wider electrical issues like cluster resets caused by plow operation, using harness P/N 84043394.

Platform-Specific Known Issues

• Per TSB #PIT5412D, flickering or inoperative headlights with code B2699 when a snowplow is installed is not an issue with the truck's headlight system. The bulletin directs technicians to contact the snowplow manufacturer for information on their headlight changeover system and to reference GM Upfitter Bulletin #116.
• GM Upfitter Bulletin #116 explains the technical reason for the fault: the BCM performs a diagnostic check upon commanding the low beams on. If an aftermarket module switches from the truck lights to the plow lights *after* this check, the BCM sees the new current inrush as a short-to-ground and disables the circuit for protection.
• Some owners may also experience other electrical issues when operating a snowplow, such as the instrument cluster or radio resetting. This is due to voltage overshoots ('load dump') when the high-current plow motor is disengaged. GM released a separate jumper harness (P/N 84043394) to address this specific concern, detailed in GM Upfitter Bulletin 124.

Hidden / Shadow Codes Worth Checking

• B2699 01: Right Low Beam Control Circuit Short to Voltage. The BCM has detected that the control circuit is shorted to a power source. (see via A professional scan tool like the GM GDS2 can read symptom bytes (the two digits after the main code).)
• B2699 02: Right Low Beam Control Circuit Short to Ground. This is the most common variant seen with incompatible snowplow modules. (see via A professional scan tool like the GM GDS2 can read symptom bytes (the two digits after the main code).)
• B2699 04: Right Low Beam Control Circuit Open. This can be caused by a broken wire or a simple burned-out headlight bulb. (see via A professional scan tool like the GM GDS2 can read symptom bytes (the two digits after the main code).)

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): BCM > Output Controls > Exterior Lighting > Right Low Beam Headlamp — After disconnecting the primary suspect (snowplow harness), this bidirectional command allows a technician to directly command the BCM to activate the right low beam circuit. If the headlight illuminates with this command, it proves the BCM, wiring, and bulb are functional, isolating the fault to the disconnected equipment or a logic issue.

Wiring & Ground Locations

• BCM Connector X5 — The Body Control Module (BCM) is located in the driver's side footwell, near or below the parking brake mechanism. It has several large multi-pin connectors, often color-coded.. The control circuit for the right low beam originates at a specific pin on one of these connectors (typically X5 or X6 on K2XX trucks). A technician would probe the wire at this connector to verify if the BCM is sending the command, or if there is a short in the harness downstream from this point.
• G103 / G105 — These are primary engine bay ground points located on the front of the cylinder heads or on the engine block itself. Another key ground is on the frame behind the front wheels.. While less likely to be the direct cause of a single headlight code, poor grounds can cause a wide range of bizarre electrical issues. Verifying that the main BCM and forward lighting grounds are clean and tight is a crucial step in any electrical diagnosis. A poor ground can increase resistance and cause the BCM to misinterpret circuit conditions.
• Underhood Fuse Block — Located in the engine compartment, typically on the driver's side.. The power for the headlight circuits runs through this fuse block. For 2017-2019 models, fuse F58 is often associated with the headlight circuits. Checking this fuse is a preliminary step, though the BCM's circuit protection often trips before a fuse blows.

Model Year Variations Within This Range

• 2016-2019: For the 2016 model year, the Sierra 1500 received a mid-cycle refresh that included new front fascia, grille, and headlight assemblies, with higher trims like the Denali getting new LED units. The 2500/3500 HD models followed suit. While the physical headlight assemblies are different and not interchangeable with 2015 models, the underlying BCM control logic and sensitivity to aftermarket modules that causes code B2699 remained the same across the 2015-2019 range.