P3055 on 2017-2021 Buick Enclave: Start/Stop System Fault Causes and Fixes

What's Unique About the 2017-2021 Buick ENCLAVE

The Buick Enclave, particularly in these model years, relies on a specific DC/DC converter to manage its Auto Start/Stop functionality (RPO code KL9). This system is shared across a vast number of GM vehicles, including the Chevy Traverse, 🎬 Watch: A quick PSA on P3055 for Traverse platform mates. GMC Acadia, and Cadillac XT5. GM has issued several Technical Service Bulletins (TSBs) for this exact code, pointing to common issues like faulty modules, wiring shorts, and even poor ground connections from the factory. Unlike generic codes, P3055 on an Enclave is almost exclusively tied to this specific voltage-stabilizing system for the start/stop feature.

Diagnostic Flowchart

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

Generation note: The 2017-2021 range covers the end of the first generation (2017) and the beginning of the second generation (2018-2021). However, Technical Service Bulletin #21-NA-139 explicitly lists the entire 2017-2021 model year range for the Buick Enclave, indicating this issue and its causes are common to both generations sharing the RPO KL9 start/stop system. The second generation began sale in late 2017 for the 2018 model year, featuring significant redesigns, but the core electrical issue related to P3055 remains consistent.

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on.
• Auto Start/Stop system is inoperative.
• Message on Driver Information Center (DIC) regarding the start/stop system.
• Infotainment screen may reboot or flicker when the vehicle comes to a stop.
• In some cases on platform mates, severe electrical issues like loss of power steering, erratic instrument cluster behavior, or the vehicle not being able to shift out of Park.
• In rare cases, other strange electrical behavior like automatic door locks engaging unexpectedly.

Most Likely Causes

1. Faulty DC/DC Converter Module 🔴 High Probability TSB #21-NA-139 suggests the module can be mis-configured or fail internally, preventing it from boosting voltage correctly. It is a very common failure point across all GM vehicles using this system.
   How to confirm: After ruling out wiring and ground issues per TSB 21-NA-139, the module is condemned. If diagnostic tests show infinite resistance to ground on the specified circuit, the TSB directs replacement of the module.
   Typical fix: Replace the T19 Power Supply Transformer 🎬 Watch: A walkthrough of the multifunction power supply replacement. (DC/DC Converter). It is typically located in the passenger-side interior, possibly behind the glove box or kick panel, and does not require programming.
   Est. part cost: $150-$250
2. Poor Ground Connection 🟡 Medium Probability A related TSB for other GM models (#18-NA-247) specifically identifies poor ground connections (G104, G107, G108) as a cause for P3055 due to issues like paint overspray or corrosion at the contact points on the frame or engine block.
   How to confirm: Locate the relevant ground points on the chassis and engine. Disconnect, clean all contact surfaces to bare metal, re-torque the fasteners to specification, and check resistance.
   Typical fix: Clean and secure ground connections. No parts are typically required.
   Est. part cost: $0
3. Short or Open in Wiring Harness ⚪ Low Probability Wiring can chafe against other components over time, leading to a short to ground or a short to voltage. A specific Preliminary Information bulletin (PIP5559) points to a potential short to voltage on circuit 2172 inside the instrument panel fuse block (X51A) on some GM models.
   How to confirm: TSB #21-NA-139 provides a detailed diagnostic procedure involving checking for shorts to voltage or ground on circuit 2172 at terminal 10 of the DC/DC converter connector.
   Typical fix: Repair the damaged section of the wiring harness.
   Est. part cost: $5-$20
4. Weak or Failing 12V Battery ⚪ Low Probability The start/stop system is highly sensitive to battery health. A weak battery may not provide the stable voltage the DC/DC converter expects, triggering a performance code. The system is designed to be disabled if battery health is low.
   How to confirm: Test the main 12V battery with a professional-grade battery tester that can measure cold cranking amps (CCA) and overall health, not just voltage.
   Typical fix: Replace the 12V AGM battery.
   Est. part cost: $200-$350

Rare But Worth Checking

• Incorrect Fuses in Fuse Block: A TSB for some GM trucks (#21-NA-121) found that P3055 could be set if fuses were installed in empty slots from the factory on vehicles with the start/stop system. It's a quick and easy check to perform on the instrument panel fuse block.
• Internal Short in Instrument Panel Fuse Block: GM Preliminary Information bulletin PIP5559 identified a rare condition on some models where circuit 2172 (a red wire with a yellow stripe) can chafe against a metal terminal inside the X51A Instrument Panel Fuse Block, causing a short to voltage. This requires removing the fuse block to inspect the wiring on the back side.

Diagnosis Steps

1. Read all fault codes from the ECM and other modules. Note if P3056 is also present, as this is very common.
2. Check the health of the main 12V battery using a professional tester. A weak battery can cause various electrical issues and will disable the start/stop system by design.
3. Inspect the instrument panel fuse block to ensure there are no incorrect fuses installed, per the logic in TSB 21-NA-121.
4. Locate, disassemble, and clean the main engine and chassis ground connections, especially G104, G107, and G108 if applicable to your vehicle's specific layout, as recommended by TSB 18-NA-247. Ensure a clean metal-to-metal contact.
5. If grounds and battery are good, proceed with the specific diagnostic steps in TSB #21-NA-139. At the T19 Power Supply Transformer connector, test for a short to voltage on circuit 2172 (terminal 10).
6. If no short to voltage is found, test for a short to ground on the same circuit (terminal 10). If the resistance is infinite (no short), the TSB directs you to replace the DC/DC Converter.
7. If the resistance is less than infinite, repair the short to ground on circuit 2172.
8. If all wiring and grounds are confirmed to be good, replace the DC/DC Converter (T19 Power Supply Transformer).

Parts You'll Likely Need

• Multifunction Power Supply Converter (DC/DC Converter) (OEM #13510484 (supersedes 13462012, 13506066, 13509853, 13514044)) — This module is the central component for the system that triggers code P3055. TSB #21-NA-139 identifies it as the likely failed part if wiring and grounds are good. It is a very common failure point.
  Trusted brands: ACDelco (OEM), GM Genuine Parts
  OEM price range: $150-$250
  Aftermarket price range: $120-$200

Related Codes That Often Appear With This One

• P3056 — P3056 is for 'DC/DC Converter Actuator Voltage 2 Performance'. The DC/DC converter has multiple channels, and it's very common for both fault codes to appear together, pointing strongly to a problem 🎬 See how P3055 and P3056 codes appear together in action. with the converter itself or its primary connections.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-139: Malfunction Indicator Lamp (MIL) Illuminated – DTC P3055 Set. This is the primary bulletin for the 2017-2021 Enclave and many other GM vehicles. It points to a mis-configured or failed DC/DC converter and provides a specific wiring test procedure to follow before replacement.
• 18-NA-247: Malfunction Indicator Lamp (MIL) Illuminated - DTC P3055 and/or P3056 Set. Although for the Equinox/Terrain, it highlights poor ground connections (G104, G107, G108) as a key cause, which is valuable information for all affected platforms.
• PIP5559: P3055 MIL SES Circuit 2172 Short To 12 Volts. This preliminary bulletin describes a rare but specific failure where wiring can chafe and short inside the instrument panel fuse block.

Platform-Specific Known Issues

• This vehicle is covered by TSB #21-NA-139, which outlines a specific diagnostic path for P3055, often leading to the replacement of the DC/DC converter module.
• The DC/DC converter module is typically located inside the vehicle on the passenger side, possibly behind the glove box or kick panel, and is a relatively easy part to access and replace with no programming required.

Mechanic-Grade Diagnostic Values

• Resistance check on Circuit 2172 — expected: Infinite resistance (OL) between terminal 10 of the T19 connector and ground.. Failure: A resistance reading of less than infinite indicates a short to ground on the circuit.
• Voltage check on Circuit 2172 — expected: A test lamp connected between terminal 10 of the T19 connector and ground should NOT illuminate.. Failure: If the test lamp turns on, it indicates a short to voltage on circuit 2172.
• Scan Tool Live Data — expected: Monitor 'DC to DC Converter Output Voltage Variance' PIDs. While specific values aren't given, these should be stable. Erratic readings or large variances during an auto-stop event can indicate a problem.. Failure: Sudden drops or spikes in voltage variance coinciding with the fault.

Scan Tool Commands That Help

• GDS2 (GM Dealer Tool): Data Display > Engine Control Module > Auto Stop/Start Data — To monitor live data PIDs such as 'DC to DC Converter Output Voltage 1' and 'DC to DC Converter Output Voltage Variance' during diagnosis to see the module's performance in real-time.
• GDS2 (GM Dealer Tool): Data Bus Diagnostic Tool — If multiple communication codes are present with P3055, this tool can be used to verify which modules on the CAN bus are communicating, helping to isolate a broader electrical issue.

Wiring & Ground Locations

• T19 — The connector for the Multifunction Power Supply Converter (DC/DC Converter), typically located on the passenger side of the cabin, behind the glove box or kick panel.. This is the main connector where diagnostic tests for shorts to voltage or ground on circuit 2172 are performed.
• Circuit 2172 — A red wire with a yellow tracer stripe that runs from the instrument panel fuse block to terminal 10 of the T19 connector.. This is the '12 volt regulated supply voltage 1' circuit. TSBs point to this specific circuit being shorted to ground or voltage as a primary cause of the code.
• X51A — The Instrument Panel Fuse Block, typically located inside the cabin, accessible from the driver or passenger side.. A rare cause of P3055 is an internal short within this fuse block, where circuit 2172 chafes against another terminal in cavity 55.

Real Owner Repair Stories

• YouTube user comment on video '2017 cruze multifunction Power Supply p3055' (2017 Chevy Cruze (platform-mate with shared system)) — P3055 and multiple other electrical codes (P3051, P3052, P3056, etc.), entire dashboard and HVAC controls stopped working, smell of burnt wires.
  ❌ Tried (didn't work) Dealer wanted to replace multiple modules for over $2,500.
  ✅ What actually fixed it The owner found that a disconnected wire had allowed water to enter the vehicle and pool in the area where the control modules were located. The lowest module, the Multifunction Power Supply, was submerged and damaged. The owner replaced the module, cleaned the corroded connectors on the other modules with vinegar and baking soda, and dried everything out, which resolved all issues.

OEM Part Supersession History

• 13462012, 13506066, 13509853, 13514044 → 13510484 — Standard part evolution for improved reliability or manufacturing changes.
  Heads up: The newest part number, 13510484, is the correct service replacement for all prior versions and is specified in TSB 21-NA-139.

Model Year Variations Within This Range

• 2017 vs 2018-2021: The 2017 model year was the final year of the first generation, while 2018 marked a complete redesign for the second generation, including a new engine and a 9-speed transmission instead of a 6-speed. However, despite the platform change, the RPO KL9 start/stop system and the associated P3055 fault are common to both generations within this range, as confirmed by TSB 21-NA-139.