P3055 on 2019-2021 Chevrolet Blazer: Stop/Start System Fault Causes and Fixes

What's Unique About the 2019-2021 Chevrolet BLAZER

The 2019-2021 Blazer, built on the GM C1XX platform, uses an auto stop/start system (RPO code KL9) to improve fuel economy. This system relies on a dedicated DC/DC converter to manage the vehicle's electrical load when the engine is off. While the technology is not unique to the Blazer, this specific component has been identified in GM Technical Service Bulletins as a common point of failure across multiple models sharing this platform, including the Chevy Traverse and GMC Acadia, leading to the P3055 code.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on.
• Auto Stop/Start system is inoperative.
• Radio or infotainment screen may intermittently shut off and restart, especially after an auto-stop.
• Power steering may feel heavy or a 'Service Power Steering' message may appear.
• Multiple warning lights on the dashboard, often including communication-related errors.
• Vehicle may shift erratically or feel sluggish.
• Doors may lock themselves during or after an auto-stop event.
• In rare cases, the vehicle may not shift out of park or fail to start.

Most Likely Causes

1. Faulty DC/DC Converter Module 🔴 High Probability As noted in GM TSB 21-NA-139, the module itself can be misconfigured or simply fail, causing Channel 1 to not boost voltage properly. It's a widely reported failure point on GM vehicles with the stop/start system, including the Blazer's platform mates like the Traverse.
   How to confirm: Follow the diagnostic procedure in TSB 21-NA-139. After confirming the wiring and grounds are good, the final step is to replace the converter module. The TSB outlines testing for shorts to voltage and ground on circuit 2172 at terminal 10 of the module's connector.
   Typical fix: Replace the Multifunction Power Supply Converter (also called the T19 Power Supply Transformer). The replacement does not require programming.
   Est. part cost: $100-$200
2. Poor Ground Connections 🟡 Medium Probability TSB 18-NA-247, written for similar GM SUVs, highlights that factory paint or corrosion on grounding studs can create poor connections, leading to voltage-related codes like P3055.
   How to confirm: Locate, inspect, and test the resistance of the main body and engine grounds. TSB 18-NA-247 specifically calls out grounds G104, G107, and G108. Look for paint, corrosion, or loose fasteners at these connection points.
   Typical fix: Remove the ground connection, thoroughly clean any paint or corrosion from the contact surfaces (eyelet and body/frame), and securely re-torque the fastener. This repair requires no parts.
   Est. part cost: $0
3. Wiring Harness Issue (Short/Open) ⚪ Low Probability While less common than a failed module, a wire can chafe against the chassis or another component, causing a short to ground or voltage.
   How to confirm: TSB 21-NA-139 outlines a specific test using a test lamp and multimeter to check for shorts on circuit 2172 at the module's connector (terminal 10).
   Typical fix: Repair the damaged section of the wiring harness.
   Est. part cost: $0-$20

Rare But Worth Checking

• Weak or Failing 12V Battery: While P3055 points to the DC/DC converter, the entire electrical system, especially the stop/start function, is sensitive to the main battery's health. An aging AGM battery can cause low voltage conditions during auto-stop events that the system interprets as a converter fault, triggering this code as a secondary issue.

Diagnosis Steps

1. Verify the battery and charging system are in good health. Use a proper AGM battery tester. A weak battery is a known cause of secondary electrical faults.
2. Scan for all DTCs in all modules. Note any other codes, especially P3056 or any U-codes, as they provide context.
3. Inspect the wiring and connector at the DC/DC Converter Module (T19 Power Supply Transformer) for any visible damage. The module is typically located under the center console.
4. Following the procedure in TSB 21-NA-139, test for a short to voltage on circuit 2172 at terminal 10 of the converter's connector.
5. If no short to voltage is found, test for a short to ground on the same circuit.
6. Inspect and clean the primary ground locations, specifically G104, G107, and G108 as specified in TSB 18-NA-247, ensuring a clean metal-to-metal contact.
7. If all wiring and grounds test good, the cause is most likely the DC/DC Converter Module itself.

Parts You'll Likely Need

• Multifunction Power Supply Converter (OEM #13510484) — This is the component that fails most frequently, as documented in GM's service bulletins for this specific code.
  Trusted brands: ACDelco (OEM), GM Genuine Parts
  OEM price range: $120-$180
  Aftermarket price range: $90-$150

Related Codes That Often Appear With This One

• P3056 — This code is for 'DC/DC Converter Output Voltage 2 Performance'. The converter has multiple channels, and it's common for both faults to be logged together when the module fails.
• U-codes (e.g., U0121, U0140, U0403) — These are communication codes. A failing DC/DC converter can cause voltage fluctuations that disrupt communication between various modules like the Power Steering Control Module or Brake Module, leading to a cascade of communication faults.
• C0800 — This code, for 'Control Module Power Circuit Low Voltage' and often found in the Power Steering Control Module, is a strong indicator that the failing DC/DC converter is causing system-wide voltage sags.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-139: Malfunction Indicator Lamp (MIL) Illuminated - DTC P3055 Set. The primary TSB for this issue. It identifies the cause as a potentially misconfigured module, provides specific wiring tests for circuit 2172, and lists affected vehicles including the Blazer.
• PIE0628: A preliminary information bulletin that acknowledges DTC P3055 on the 2020 Blazer and requests data from technicians encountering the issue.
• 18-NA-247: Malfunction Indicator Lamp (MIL) Illuminated - DTC P3055 and/or P3056 Set. Though written for the Equinox/Terrain, it provides a valuable secondary cause: poor ground connections at points G104, G107, and G108 due to factory paint.
• 17-NA-022: Warns technicians not to replace the power supply transformer until the wiring harness has been validated, reinforcing the diagnostic principle of checking wiring first.

Platform-Specific Known Issues

• GM issued Technical Service Bulletin 21-NA-139 specifically for the 2019-2021 Blazer (and other models) to address DTC P3055. The bulletin provides a clear diagnostic path and identifies the likely cause as a misconfigured or failed DC/DC module.

Mechanic-Grade Diagnostic Values

• Short to Voltage on Circuit 2172 — expected: A test lamp connected between terminal 10 of the T19 connector and a known good ground should NOT turn on.. Failure: If the test lamp illuminates, it indicates a short to voltage on circuit 2172 that must be repaired.
• Short to Ground on Circuit 2172 — expected: Infinite resistance between terminal 10 of the T19 connector and ground (with relevant fuses removed).. Failure: A resistance reading of less than infinite indicates a short to ground on the circuit that must be repaired.

Scan Tool Commands That Help

• GDS2 or equivalent professional scan tool: Monitor Live Data PID: 'DC to DC Converter Output Voltage Variance' — This PID should be monitored during diagnosis to observe the performance of the converter in real-time. Unstable or out-of-spec readings can help confirm a faulty module.

Wiring & Ground Locations

• T19 Power Supply Transformer Connector — On the Multifunction Power Supply Converter, located under the center console.. This is the main connector for the module. Terminal 10 on this connector, for circuit 2172, is the specific point for electrical testing per TSB 21-NA-139.
• G104, G107, G108 — These are chassis and engine ground points. While their exact location on the Blazer requires consulting GM Service Information, TSB 18-NA-247 identifies them as common problem areas on related platforms.. Poor connections at these grounds, often due to factory paint, can cause voltage drops and trigger P3055. Cleaning these grounds is a key diagnostic step before replacing parts.

Real Owner Repair Stories

• YouTube - 'Quick PSA: 2018 and up Chevy Traverse P3051 P3055' (2018 Chevrolet Traverse (platform mate)) — All lights on the dash, power steering inoperative (hard to turn), radio acting up, erratic shifting, and over 20 communication codes across various modules.
  ❌ Tried (didn't work) The technician notes that simply clearing the codes would be ineffective as the problem would return quickly because it's a hardware fault.
  ✅ What actually fixed it Replacing the T19 Power Supply Transformer (DC/DC converter). The technician confirmed the diagnostic path from the TSB (testing for shorts, finding none) led directly to replacing the module as the final step. He noted it's a common failure and the replacement part requires no programming.
• YouTube - '2016 Chevy Malibu dtc P3055 P3056' (2016 Chevrolet Malibu (uses similar system)) — P3055 and P3056 codes present.
  ❌ Tried (didn't work) Attempting to replace the module by only pulling back the carpet without removing the center console proved extremely difficult and risky.
  ✅ What actually fixed it The video is a tutorial on the replacement. The key takeaway and advice for the final fix is that removing the entire center console (a ~15 minute job) makes replacing the module much easier and safer. Crucially, the technician notes that if the module is disconnected, the car will be in a no-start condition and will not recognize the key fob.

OEM Part Supersession History

• 13462012, 13506066, 13509853, 13514044 → 13510484 — GM has released several revisions of this part to improve reliability. TSB 17-NA-022 from 2017 specified part number 13514044, which has since been superseded itself.
  Heads up: The newest part number (13510484) is the correct and most current replacement for all previous versions and should be used for repairs.