B2699 on 2017 GMC Sierra: Right Low Beam Circuit Fault Causes & Fixes

What's Unique About the 2017-2017 Gmc SIERRA

For this generation of GMC Sierra (and its sibling, the Chevy Silverado), code B2699 is uniquely and strongly associated with aftermarket snowplow installations. General Motors has issued multiple Technical Service Bulletins (TSBs) stating that when B2699 appears, the root cause is almost always an issue with the snowplow's headlight changeover module. The truck's sensitive BCM performs a diagnostic check when the low beams are commanded on. As explained in GM Upfitter Bulletin #116, if an aftermarket module switches from the truck lights to the plow lights *after* this check, the BCM sees the new current path as a fault (often a short-to-ground) and disables the headlight driver to protect itself.

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 does not turn on.
• Headlights (both truck and plow) flicker or are inoperative when switching between them.
• A "Service Headlamp System" message may appear on the driver information center.
• The code B2699 is present in the BCM, often accompanied by B2575 for the left headlight.

Most Likely Causes

1. Improperly Installed or Faulty Snowplow Headlight Wiring/Module 🔴 High Probability The BCM's circuit protection logic is sensitive and often incompatible with older or improperly designed aftermarket headlight changeover modules used for snowplows. This is confirmed by multiple GM TSBs.
   How to confirm: Visually check for a snowplow wiring harness. Disconnect the main plow electrical harness from the truck, clear the codes, and see if B2699 returns. If it does not, the fault is in the plow's system.
   Typical fix: Contact the snowplow manufacturer for an updated, compatible headlight module or wiring harness. For many Western, Fisher, and SnowEx plows, this involves installing a 3-Port Isolation Module (Part #29070-1). Refer to GM 🎬 Watch: How to install a Western plow wiring module. Upfitter Integration Bulletin #116 for correct installation procedures.
   Est. part cost: $50-$350
2. Damaged Wiring or Corroded Connector 🟡 Medium Probability Wiring in the engine bay is exposed to heat, moisture, and vibration, which can lead to chafing, breaks, or corrosion over time, especially at the headlight connector pigtail.
   How to confirm: Visually inspect the wiring harness leading to the right headlight. Use a multimeter to check for continuity, voltage, and short-to-ground on the control circuit wire between the BCM and the headlight connector.
   Typical fix: Repair the damaged section of wire or replace the headlight pigtail connector. Ensure the connection is clean and secure.
   Est. part cost: $15-$50
3. Incompatible Aftermarket LED/HID Headlight Bulbs ⚪ Low Probability → Shop Headlight Bulb The BCM is calibrated for the specific electrical signature of a halogen bulb. Installing aftermarket LED or HID bulbs without a proper CANbus decoder or anti-flicker harness can present an electrical load the BCM misinterprets as a fault, setting B2699.
   How to confirm: If aftermarket bulbs are installed, temporarily reinstall the original factory halogen bulbs. Clear the code and see if it returns. If the code does not return with the halogen bulbs, the aftermarket bulbs or their supporting hardware are the cause.
   Typical fix: Remove the aftermarket bulbs or install a high-quality CANbus-compatible decoder/harness designed for the vehicle.
   Est. part cost: $25-$75
4. Failed Headlight Bulb ⚪ Low Probability → Shop Headlight Bulb While a burnt-out bulb is a common failure, it typically creates an open circuit (B2699 04). On this truck, the BCM is more likely to set this specific code due to short circuits from plow wiring rather than a simple bulb failure.
   How to confirm: Swap the right and left low beam bulbs. If the problem moves to the left side (and now sets a B2575 code), the bulb is bad. The 2017 Sierra typically uses a 9012 (HIR2) bulb. 🎬 See this walkthrough for replacing the passenger side headlight bulb.
   Typical fix: Replace the headlight bulb.
   Est. part cost: $20-$40

Rare But Worth Checking

• Failed Body Control Module (BCM): → Shop Body Control Module This is a rare failure. The BCM is the computer that controls the headlights, but it should only be considered after all wiring, bulbs, and especially any aftermarket equipment have been definitively ruled out. Replacement requires programming by a dealer or qualified shop. The OEM part 🎬 Watch: How to locate the BCM on your truck. is often an ACDelco unit.

Diagnosis Steps

1. Check if the truck is equipped with a snowplow or has a plow wiring harness installed. This is the most critical first step.
2. If a plow harness is present, consult GM TSB #PIT5412D. The bulletin advises that this is not an issue with the truck's system and to contact the snowplow manufacturer for their specific fix.
3. As a diagnostic test, completely disconnect the snowplow's main electrical harness from the truck. Clear the DTCs with a scan tool and cycle the headlights. If code B2699 does not return, the fault is confirmed to be within the snowplow's electrical system.
4. If no plow equipment has ever been installed, check for aftermarket LED or HID bulbs. If present, swap them with standard halogen bulbs to see if the fault clears.
5. Inspect the right headlight bulb and its electrical connector for any signs of burning, corrosion, or damage.
6. Swap the right and left low beam bulbs to quickly rule out a faulty bulb.
7. Using a multimeter and wiring diagram, test the right low beam control circuit (referencing the specific fault type like short to ground or open). Check for continuity, short to ground, and short to voltage between the BCM connector and the headlight connector.
8. If all wiring, the bulb, and any aftermarket equipment are confirmed to be good, the Body Control Module (BCM) may be faulty, but this is the least likely cause.

Parts You'll Likely Need

• Snowplow Headlight Isolation Module (OEM #29070-1 (Western/Fisher/SnowEx 3-Port Module)) — This is the most frequent cause of B2699 on plow-equipped trucks. The original module is often not compatible with the BCM's circuit protection logic. The correct part must be sourced from the plow manufacturer.
  Trusted brands: Western, Fisher, BOSS, SnowEx
  OEM price range: $150-$350
• Low Beam Headlight Bulb (OEM #9012 (HIR2)) — If the fault is a simple open circuit and no plow is installed, a burnt-out bulb could be the cause.
  Trusted brands: ACDelco, Sylvania, Philips
  OEM price range: $30-$50
  Aftermarket price range: $20-$40
• Body Control Module (BCM) (OEM #ACDelco 23476221) — This is the last resort if all wiring, bulbs, and aftermarket modules are confirmed to be working correctly. It is a rare failure point for this code.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $300-$500
  Aftermarket price range: $200-$400

Related Codes That Often Appear With This One

• B2575 — This is the corresponding code for the Left Headlamp Control Circuit. They often appear together because aftermarket snowplow modules interface with both headlight circuits and can cause faults on both sides simultaneously.

Technical Service Bulletins (TSBs) & Recalls

• PIT5412D: Addresses flickering or inoperative truck or snowplow headlights, mentioning codes B2575 and/or B2699. It directs technicians to contact the snowplow manufacturer and references Bulletin 116.
• GM Upfitter Integration Bulletin #116: The core technical document explaining how the BCM headlight circuit works and why certain aftermarket modules cause faults. It is the document all other TSBs on this topic refer to.
• PIT5412C: An earlier version of PIT5412D, covering models up to 2018.
• PIT5412A/B: Even earlier versions of the bulletin with the same fundamental guidance.

Platform-Specific Known Issues

• GM Technical Service Bulletin PIT5412D explicitly notes that flickering or inoperative headlights with codes B2699 and B2575 on trucks with snowplows is an issue with the snowplow manufacturer's headlight changeover system, not the truck itself.
• GM Upfitter Integration Bulletin #116 explains the technical reason for the fault: the BCM performs a diagnostic check when the low beams are commanded on. If an aftermarket module switches from the truck lights to the plow lights *after* this check, the BCM sees the new current draw as a short-to-ground and disables the circuit for protection.

Mechanic-Grade Diagnostic Values

• Right Low Beam Control Circuit Voltage — expected: Battery Positive Voltage (approx. 12-14V) when commanded ON by the BCM.. Failure: 0V may indicate an open circuit or a BCM driver that has shut down. Voltage present when commanded OFF could indicate a short to voltage.
• Continuity between BCM and Headlight Connector — expected: Less than 2 ohms on the control circuit wire.. Failure: Resistance of 2 ohms or greater (or OL) indicates an open or high resistance in the wire.
• Resistance to Ground on Control Circuit — expected: Infinite resistance (OL) with the headlight and BCM disconnected.. Failure: Any reading showing continuity to ground indicates a short circuit.

Hidden / Shadow Codes Worth Checking

• B2699 01: Right Headlamp Control Circuit Short to Battery. This indicates the BCM has detected constant voltage on the circuit, even when it's supposed to be off. (see via A professional scan tool like GM GDS2 will display these two-digit symptom bytes.)
• B2699 02: Right Headlamp Control Circuit Short to Ground. This is the most common variant seen with snowplow module issues, where the BCM driver detects an excessive current draw. (see via A professional scan tool like GM GDS2 will display these two-digit symptom bytes.)
• B2699 04: Right Headlamp Control Circuit Open. This typically points to a broken wire, loose connection, or a simple burnt-out bulb. (see via A professional scan tool like GM GDS2 will display these two-digit symptom bytes.)

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Body Control Module > Control Functions > Exterior Lighting > Low Beam Headlamps — This bidirectional command allows a technician to manually toggle the right low beam ON and OFF directly from the scan tool. If the headlight works with this command, it confirms the BCM driver, wiring, and bulb are likely okay, pointing the diagnosis toward an input or logic issue. If it fails to light up, it confirms the fault is in the BCM, wiring, or bulb.

Wiring & Ground Locations

• BCM Connector X5 — The Body Control Module (BCM) is located on the lower left side of the dashboard, accessible by removing the driver's side knee bolster. It has several large connectors; X5 is typically the brown one.. The control circuit for the right low beam headlight originates from a pin on this connector. A wiring diagram is needed to identify the exact pin number and wire color (which can vary), but all circuit testing begins or ends at this point.
• G105 — Located at the right front of the engine compartment, often behind the headlight assembly on the radiator support.. This is a primary ground point for the right side headlight assembly. A loose or corroded connection at G105 can cause an open circuit (B2699 04) or flickering, even if the control circuit from the BCM is good.
• G218 — Located on the left (driver's) side, behind the dash panel near the A-pillar. It is a stud with multiple ground wires attached.. This is a major interior ground point that serves the Body Control Module (BCM). While not a direct headlight ground, a poor connection here (often due to trapped dash insulation from the factory) can cause a wide range of bizarre electrical issues, including BCM malfunctions that could potentially trigger headlight codes. A TSB (PIT5405C) addresses issues with this ground.

Real Owner Repair Stories

• gm-trucks.com forum user (2016 Chevrolet Silverado (same platform)) — Right low beam headlight inoperative, code B2699 set.
  ❌ Tried (didn't work) Replacing the headlight bulb., Checking fuses.
  ✅ What actually fixed it The user confirmed a snowplow was installed. The final fix was installing the Western 3-port isolation module (Part #29070-1) to make the plow's lighting system compatible with the truck's BCM. The code did not return after the correct module was installed.