B2699 on 2015-2019 GMC Sierra 2500: Right Headlamp Circuit Fault Causes and Fixes

What's Unique About the 2015-2019 Gmc SIERRA 2500

On the GMC Sierra 2500 heavy-duty platform (K2XX), this code is uniquely tied to aftermarket equipment, especially snowplows. The BCM in these trucks is highly sensitive to the electrical loads and timing of headlight switching. Aftermarket headlight changeover modules used for snowplows can cause a delayed current draw that the BCM misinterprets as a short circuit, triggering the code. General Motors has issued multiple Technical Service Bulletins (TSBs) and an Upfitter bulletin confirming that this issue originates with the up-fitter equipment, not the truck itself. GM Upfitter Bulletin #116 explains that the BCM performs a diagnostic check the instant the lights are turned on; a delayed current inrush from a plow module switching lights is flagged as a short circuit, causing the BCM to disable the output.

Diagnostic Flowchart

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

Symptoms You May Notice

• The right low-beam headlight is inoperative.
• Headlights (either the truck's or the plow's) flicker or do not work when switching between them.
• A "Service Headlamp System" message appears on the driver information center.
• The right headlight may stay on continuously and cannot be turned off (in case of a short to voltage).
• Code B2699 is often accompanied by B2575 (Left Headlamp Control Circuit).

Most Likely Causes

1. Faulty or Incompatible Snowplow Headlight Module/Wiring 🔴 High Probability As documented in GM TSBs like PIT5412D, the BCM's circuit protection logic is sensitive and often incompatible with the delayed switching of aftermarket snowplow headlight modules. GM Upfitter Bulletin #116 explains that the BCM performs a diagnostic check when the lights are turned on; a delayed current inrush from a plow module is flagged as a short circuit. This is the most common cause on these work-oriented trucks.
   How to confirm: Disconnect the main electrical harness for the snowplow from the truck. Clear the codes with a scan tool. If code B2699 does not return after cycling the headlights, the fault is in the snowplow's electrical system.
   Typical fix: Contact the snowplow manufacturer for an updated headlight changeover module or wiring harness specifically designed for 2015+ GM trucks. 🎬 Watch: Troubleshooting and fixing Western snow plow headlight issues. For Western, Fisher, SnowEx, and Blizzard plows, this often involves installing harness kit #69818-2, which is designed for 2015-2019 GM 2500/3500 trucks. This kit works with the 3-port isolation module (Part #29070-1). Some newer modules are called 'soft start' modules, like part #29760-2.
   Est. part cost: $150-$400
2. Damaged Headlight Wiring or Connector 🟡 Medium Probability This is a potential issue on any vehicle, but on work trucks like the Sierra 2500, the harnesses are more exposed to harsh conditions, vibration, and potential damage during up-fitting or maintenance. The connector itself can also melt from high resistance.
   How to confirm: With the plow harness disconnected (if applicable), visually inspect the factory headlight connector and surrounding wires for corrosion, melted plastic, or broken strands. Use a multimeter to test the control circuit for continuity, a short to ground, or a short to power.
   Typical fix: Repair the damaged section of the wiring harness or replace the pigtail connector for the headlight assembly. An aftermarket pigtail like Dorman 85897 or an equivalent is often used.
   Est. part cost: $15-$50
3. Burnt-Out Headlight Bulb ⚪ Low Probability While a burnt-out bulb is a common maintenance item, it's less likely to be the primary cause of B2699 compared to up-fitter issues on this specific truck. A simple open circuit from a bad bulb filament can sometimes trigger the code, specifically B2699 04.
   How to confirm: Swap the right low-beam bulb with the known-good bulb from the left side. If the problem moves to the left side (and code B2575 appears), the bulb is the issue.
   Typical fix: Replace the right low-beam headlight bulb. The standard bulb type is typically a 9012 (HIR2).
   Est. part cost: $20-$60

Rare But Worth Checking

• Faulty Body Control Module (BCM): This is extremely rare and should only be considered after all wiring, bulbs, and aftermarket modules have been definitively ruled out. The BCM is a robust component, and replacing it is expensive and requires programming by a dealer or qualified shop. GM TSBs repeatedly state the issue is with the upfitter equipment, not the truck's modules.

Diagnosis Steps

1. Scan the Body Control Module (BCM) for diagnostic trouble codes. Confirm B2699 is present and check for B2575.
2. If a snowplow or other aftermarket lighting is installed, completely disconnect its main electrical harness from the truck. This is the most critical diagnostic step.
3. Clear all DTCs using a scan tool.
4. Cycle the ignition off, then on. Turn the factory headlights on and off.
5. Re-scan for codes. If B2699 does NOT return, the fault is confirmed to be in the snowplow's wiring or control module. Contact the snowplow manufacturer for support, referencing GM Upfitter Bulletin #116.
6. If the code DOES return with the plow disconnected, the fault is in the truck's factory wiring, bulb, or BCM.
7. Visually inspect the right headlight bulb. If it appears burnt out, swap it with the left side to confirm before replacing.
8. Inspect the headlight wiring connector for damage, corrosion, or loose pins. Pay close attention to signs of melting or discoloration.
9. Using a multimeter and a wiring diagram, test the right headlamp control circuit for continuity, shorts to ground, and shorts to voltage between the BCM and the headlight connector.
10. If all wiring and the bulb test normal, the issue may be a rare internal failure of the BCM, which requires professional diagnosis.

Parts You'll Likely Need

• Snowplow Headlight Changeover Module/Harness Kit (OEM #Western/Fisher/SnowEx/Blizzard Kit #69818-2) — This is the most common cause of B2699 on plow-equipped trucks. This specific kit is designed for 2015-2019 GM HD trucks to be compatible with the BCM's circuit protection logic.
  Trusted brands: Western, Fisher, BOSS, SnowEx
  OEM price range: $300-$400
• Snowplow Isolation Module (OEM #Western/Fisher #29070-1) — This is the control box that the headlight harness plugs into. It isolates the plow's electrical system from the truck's. It can fail internally, causing this code. 🎬 Watch: Understanding how Boss snowplow relays and modules function.
  Trusted brands: Western, Fisher, SnowEx
  OEM price range: $150-$250
• Low Beam Headlight Bulb (OEM #9012 / HIR2) — A burnt-out bulb can cause an open circuit fault, though it's a less common cause for this code on this truck compared to plow issues.
  Trusted brands: ACDelco, Sylvania, Philips
  OEM price range: $40-$60
  Aftermarket price range: $20-$40
• Headlight Connector Pigtail (OEM #ACDelco PT2298 (Verify)) — If the factory connector is melted or corroded, it will need to be cut out and replaced to ensure a solid connection.
  Trusted brands: ACDelco, Dorman
  OEM price range: $30-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• B2575 — This is the corresponding code for the Left Headlamp Control Circuit. Both codes often appear together when there is a systemic issue with an aftermarket headlight changeover module for a snowplow, as the module affects both headlight circuits.

Technical Service Bulletins (TSBs) & Recalls

• PIT5412D: Headlight Flicker or Inoperative When Switching Between The Truck and Snow Plow Headlights.
• PIT5412A: Snowplow Headlamps Inoperative.

Platform-Specific Known Issues

• TSB #PIT5412D explicitly states that when headlights flicker or are inoperative with code B2699 on a snowplow-equipped truck, it is not an issue with the truck's headlight system. It directs technicians to contact the snowplow manufacturer for information on their headlight changeover system.
• TSB #PIT5412A gives similar advice for inoperative snowplow headlamps, pointing technicians to GM Up-fitter Integration Bulletin 116 for more details on the circuit's operation.
• GM Upfitter Bulletin #116 is the core technical document explaining that the BCM's diagnostic algorithm expects a specific current signature upon startup. Aftermarket modules that delay this signature are misinterpreted as a fault.
• GM Upfitter Bulletin #124k discusses a related issue where the large electrical draw from the plow's hydraulic motor can cause a voltage overshoot ('load dump') when stopped, leading to instrument cluster and radio resets. This highlights the overall electrical sensitivity of these trucks to plow integration.

Mechanic-Grade Diagnostic Values

• BCM Operating Voltage — expected: 9-16 Volts. Failure: The BCM may not run diagnostics or may behave erratically if voltage is outside this range.

Hidden / Shadow Codes Worth Checking

• B2699 01: Right Headlamp Control Circuit Short to Battery. This indicates the BCM has detected battery voltage on the control circuit when it should not be present. (see via A professional GM-specific scan tool like GDS2 or a high-end bidirectional tool is required to view symptom bytes.)
• B2699 02: Right Headlamp Control Circuit Short to Ground. This is the most common symptom byte when a snowplow module causes a delayed current inrush, which the BCM interprets as a short. (see via A professional GM-specific scan tool like GDS2 or a high-end bidirectional tool is required to view symptom bytes.)
• B2699 04: Right Headlamp Control Circuit Open. This can be caused by a burnt-out bulb, a broken wire, a corroded connector, or a poor ground connection. (see via A professional GM-specific scan tool like GDS2 or a high-end bidirectional tool is required to view symptom bytes.)

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): BCM > Control Functions > Exterior Lighting > Low Beams — After disconnecting any aftermarket equipment, this bidirectional command allows a technician to manually activate and deactivate the right low beam directly from the scan tool. If the headlight works using this command, it confirms the BCM driver, wiring, bulb, and grounds are all functional, pointing definitively to a control-side issue (like the plow module or headlight switch).

Wiring & Ground Locations

• Frame Rail Grounds — On the frame rail, typically below the driver-side door and near the driver-side front tire.. These are major ground points for various vehicle systems. Corrosion or looseness here can cause intermittent or open circuits for lighting systems, potentially triggering a B2699 04 code if the plow system is not at fault.
• Firewall / Engine Block Ground Straps — Braided straps connecting the engine block to the vehicle's firewall/chassis, often at the rear of the engine bay.. These straps provide the primary ground path for the engine and body. A degraded strap can cause widespread electrical issues, including flickering lights and unpredictable module behavior.
• G218 — Reported to be located near the left front dash defroster deflector area, under the dash.. Interior grounds like this serve the BCM and other in-cab modules. A fault here is less likely but could contribute to erratic BCM behavior if other causes are ruled out.

Real Owner Repair Stories

• PlowSite Forums & Western Plows technical documentation consensus (2016 GMC Sierra 2500 with Western snowplow) — Right headlight inoperative immediately after plow installation. Codes B2699 and B2575 present. Headlights worked fine before the plow was connected.
  ❌ Tried (didn't work) Replacing the headlight bulb., Checking fuses in the truck's fuse box., Swapping headlight assemblies from left to right.
  ✅ What actually fixed it The problem was an incompatibility between the truck's BCM and the standard plow lighting module. The definitive fix was installing the Western 'soft start' module kit (Part #29760-2). This kit includes the necessary adapter harness that slows the current inrush during headlight changeover, satisfying the BCM's diagnostic parameters and preventing the code from setting.

"I Checked Everything" — The Actual Cause

• For code B2699, the electrical equivalent of a 'smoke test clean' scenario is when a technician tests the headlight wiring with a multimeter and finds no short-to-ground or open circuit. The wiring, bulb, and connector all appear to be perfect. The actual cause is a timing-sensitive fault where the snowplow's headlight changeover module draws current a split-second after the BCM performs its diagnostic check. The BCM's 'smart driver' interprets this delayed inrush as a circuit fault (typically a short) and disables the output to protect itself. A standard multimeter test performed on a static circuit will not detect this dynamic, timing-based incompatibility.

OEM Part Supersession History

• Western/Fisher 3-Port Isolation Module (e.g., 29070-1) → Western/Fisher Soft Start Module Kit (e.g., 29760-2) — Starting with 2015 model year GM trucks, the BCM's headlight circuit diagnostics became more sensitive. The older isolation modules switched too slowly, causing the BCM to falsely detect a short and set B2699/B2575. The 'soft start' module was introduced to manage the current inrush in a way that is compatible with the newer BCMs.
  Heads up: A standard 29070-1 module can be upgraded to the 'soft start' specification by adding adapter harness #76272. This is a cost-effective fix for users who already own the older module and are moving their plow to a newer truck.

Model Year Variations Within This Range

• 2015-2019: The primary difference affecting this code is not within the 2015-2019 range, but between this range and prior years. The K2XX platform introduced a more sensitive BCM diagnostic strategy for lighting circuits starting in model year 2014/2015. This change is what makes older aftermarket lighting modules incompatible and requires the use of newer 'soft start' or specifically compatible modules from upfitters to avoid setting B2699.