P3055 on 2016-2021 Chevrolet Malibu: Start/Stop System Failure Causes and Fixes

What's Unique About the 2016-2021 Chevrolet MALIBU

The ninth-generation Chevrolet Malibu (2016-2021) with the auto start/stop option (RPO code KL9) relies on a specific component called the T19 Power Supply Transformer or Multifunction Power Supply Converter. This module has proven to be a common failure point, leading GM to issue multiple Technical Service Bulletins (TSBs) about code P3055. 🎬 Watch: Diagnostic walkthrough for codes P3055 and P3056 Unlike vehicles with a simple auxiliary battery, the Malibu's issue is frequently traced back to this specific control module, which is located under the center console and requires significant interior trim removal to access.

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 Start/Stop feature is inoperative.
• Remote vehicle start does not work.
• "Service Stabilitrak" message on the dash.
• "Power Assist Reduced Drive With Care" message.
• Infotainment screen may shut off and restart during an auto-stop event.
• In rare cases, a no-start or no-crank condition.
• Doors may lock themselves during an auto-stop event.

Most Likely Causes

1. Failed DC/DC Converter (Multifunction Power Supply Converter) 🔴 High Probability This specific module is a known failure point on this platform and many other GM vehicles, as documented in multiple GM service bulletins. TSB 17-NA-022 notes that an older version of the module could be the cause.
   How to confirm: After scanning for codes P3055 and the often-related P3056, follow the diagnostic procedure outlined in TSB 21-NA-139. This involves testing for shorts to voltage or ground on circuit 2172 at terminal 10 of the module's connector. If no wiring faults are found, the module itself is the likely culprit.
   Typical fix: Replace the Multifunction Power Supply Converter module. This is a plug-and-play part that does not require reprogramming.
   Est. part cost: $100-$250
2. Poor Ground Connections 🟡 Medium Probability TSB 18-NA-247 highlights that poor ground connections (specifically G104, G107, G108 for some GM models) can cause P3055. Paint or corrosion at ground points can increase resistance and cause voltage issues. While the TSB was for the Equinox/Terrain, the principle applies broadly. For the Malibu, relevant grounds are in the engine compartment and under the center console.
   How to confirm: Locate the relevant ground points for the DC/DC converter circuit and ECM. On a 2012 Malibu, G104 and G107 are in the engine compartment, while G201 and G203 are under the center console. For the 2016+ generation, check grounds on the engine block and cowl. Inspect them for looseness, paint, or corrosion. Clean the contact surfaces and re-torque the fasteners to specification.
   Typical fix: Clean and secure the ground connections. This repair often requires no new parts.
   Est. part cost: $0
3. Wiring Harness Issue ⚪ Low Probability Wiring can chafe against vehicle components. GM Preliminary Information bulletin PIC6420B mentions that harness rubbing on the battery tray support bracket can cause a host of codes, including P3055 and P3056. Water intrusion can also be a cause, as one Cruze owner found water in the rear module area causing the failure.
   How to confirm: Perform a circuit test as described in TSB 21-NA-139. This involves using a test lamp and multimeter to check for shorts to voltage or ground on the circuit leading to the converter module. Visually inspect the wiring harness for chafing, especially near brackets and where it passes through the chassis.
   Typical fix: Repair the damaged section of the wiring harness and protect it from future damage.
   Est. part cost: $5-$50

Rare But Worth Checking

• Failing Main Vehicle Battery: While the code points to the secondary power system, a weak or failing primary 12V battery can cause widespread electrical issues and trigger various codes. One owner of a Chevy Equinox with P3055/P3056 traced the issue to a failing battery that could not maintain voltage during start-stop events. One owner on Reddit also reported that a new battery resolved their P3055 issue. A healthy battery should stabilize between 12.4V and 12.8V after the ignition is turned off.

Diagnosis Steps

1. Scan the Engine Control Module (ECM) for trouble codes. Confirm if P3055 is present, and note if P3056 is also set.
2. Check the vehicle's main 12V battery to ensure it is fully charged and healthy. A weak main battery can cause unpredictable electrical faults and should be ruled out first. Verify battery voltage stabilizes between 12.4V and 12.8V a few minutes after turning the ignition off.
3. Locate the Multifunction Power Supply Converter (T19 Power Supply Transformer). On the 2016-2021 Malibu, it is located under the center console, often requiring removal of the console for access.
4. Inspect the wiring and connectors going to the converter module for any signs of damage, corrosion, or looseness.
5. Follow the diagnostic procedure in GM TSB 21-NA-139. This involves testing for a short to voltage or a short to ground on the module's circuit (specifically circuit 2172 at terminal 10).
6. If the wiring and ground connections are confirmed to be good, the DC/DC converter module is faulty and should be replaced.

Parts You'll Likely Need

• Multifunction Power Supply Converter (OEM #13510484) — This module is the most common failure point that triggers codes P3055 and P3056. Part number 13510484 is the latest version from GM and supersedes older numbers like 13514044, 13509853, 13506066, and 13462012.
  Trusted brands: ACDelco, GM Genuine
  OEM price range: $150-$250
  Aftermarket price range: $100-$180

Related Codes That Often Appear With This One

• P3056 — This code is for 'DC/DC Converter Actuator Voltage 2 Performance.' P3055 and P3056 refer to different channels within the same converter module. They almost always appear together and point to the same root cause: a faulty converter or its wiring.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-139: Malfunction Indicator Lamp (MIL) Illuminated - DTC P3055 Set. Provides detailed diagnostic steps and lists many affected GM vehicles.
• 43890: Mentions MIL illumination with DTCs P3055 and P3056, resulting in inoperative remote start and disabled stop/start feature.
• 16-NA-093: Vehicle Remote Start Inoperative, Malfunction Indicator Lamp (Check Engine Light) ON with P3055 and/or P3056 Set.
• 17-NA-022: Points to an older version of the module being the cause and recommends replacement after validating the wiring.
• 18-NA-247: While for Equinox/Terrain, it establishes poor grounds as a potential cause for P3055.
• PIC6420B: Preliminary information bulletin noting that wiring harness chafing on the battery tray support bracket can cause P3055/P3056 among many other codes.

Platform-Specific Known Issues

• GM issued Technical Service Bulletin #43890 for the 2016 Malibu, noting that codes P3055 and P3056 can cause the remote start to be inoperative and the start/stop feature to be disabled.
• TSB #21-NA-139 provides a detailed diagnostic procedure for P3055, which can be caused by a misconfigured or failed DC/DC module. It lists the updated part number 13510484.
• TSB #16-NA-093 specifically calls for the replacement of the 'T19 Power Supply Transformer (Multifunction Power Supply Converter)' when diagnostics lead to it, citing part number 13514044 (now superseded).
• An owner of a 2016 Malibu reported codes P3055 and P3056 along with 'SERVICE STABILITRAK' and 'POWER ASSIST REDUCED' messages. [ODI #11355156]
• A YouTube video by user 'Pdub Automotive' shows the location of the converter module in a 2016 Malibu under the center of the dash and confirms that removing the center console makes the job much easier and safer than trying to sneak the part out.
• A 2020 Malibu owner also documented the replacement on YouTube, confirming the part's location under the center console and noting the difficulty in finding information for the newer model year.

Mechanic-Grade Diagnostic Values

• DC/DC Converter Actuator Voltage 1 (P3055) — expected: Should not be less than 1V or greater than 28V.. Failure: A reading less than 1V triggers DTC P3052 (Low Voltage), and a reading greater than 28V triggers P3054 (High Voltage). P3055 sets when the difference between ECM ignition voltage and the converter output is 1V or more.
• Circuit 2172 at Terminal 10 of T19 Converter for short to voltage — expected: A test lamp connected between terminal 10 and a known good ground should NOT illuminate.. Failure: If the test lamp turns on, it indicates a short to voltage on that circuit which must be repaired.
• Circuit 2172 at Terminal 10 of T19 Converter for short to ground — expected: With all fuses on the circuit removed, resistance between terminal 10 and ground should be infinite.. Failure: A resistance reading of less than infinite indicates a short to ground on the circuit.
• Main Battery Voltage (at rest) — expected: Between 12.4V and 12.8V a few minutes after turning the ignition OFF.. Failure: Voltage below 12.4V indicates a discharged or failing battery that should be tested/charged before diagnosing other components.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Body Control Module > Control Functions — While not a direct test for the P3055 code, GDS2 allows bidirectional control of various BCM outputs (lights, locks, windows). If multiple electronic systems are acting erratically along with the P3055 code, using these commands can help determine if the BCM is commanding functions correctly, which can help differentiate between a bad DC/DC converter affecting module power versus a faulty BCM.
• GDS2 (GM Global Diagnostic System 2): Data Display > Engine Control Module > Auto Stop/Start Data — This allows viewing of live data PIDs related to the start/stop system, including 'DC to DC Converter Output Voltage 1' and 'DC to DC Converter Output Voltage 2'. This is essential for observing the module's voltage output in real-time to see if it matches the conditions for setting the DTC.

Wiring & Ground Locations

• G104 — Located at the rear of the left cylinder head on the engine.. TSB 18-NA-247 for other GM models specifically calls out G104 as a potential cause for P3055 due to a poor connection. This ground is critical for the Engine Control Module (ECM).
• G108 — Located on the cowl, where a ground strap from the engine connects to the body.. This is a primary engine-to-body ground. TSB 18-NA-247 also lists this as a potential cause. A poor connection here can cause widespread electrical issues.
• G302 (example for console area) — Under the center console, often near the rear.. The T19 Multifunction Power Supply Converter is located under the center console. While specific ground points for the 2016+ Malibu require a wiring diagram, grounds in this area (like G302 on other platforms) are responsible for grounding components within the console. A poor ground near the module itself could be a cause.
• T19 Power Supply Transformer Connector X1, Pin 10 — The connector for the DC/DC converter module under the center console.. This is the specific pin for Circuit 2172 (DC/DC Converter Actuator Voltage 1) that must be tested for shorts to voltage or ground as per TSB 21-NA-139.

Real Owner Repair Stories

• NHTSA ODI #11244609 (2016 Chevrolet Malibu) — Vehicle would not start, requiring a tow. Check engine light with codes P3055 and P3056.
  ❌ Tried (didn't work) New Battery, New VCM (Vehicle Control Module), New Wiring Harness
  ✅ What actually fixed it The owner complaint does not list the final fix, but highlights that replacing the battery, a control module, and even the wiring harness did not solve the recurring P3055/P3056 codes, pointing strongly toward the DC/DC converter as the remaining likely culprit.

OEM Part Supersession History

• 13462012, 13506066, 13509853, 13514044 → 13510484 — Part has been updated by the manufacturer over time to improve reliability.
  Heads up: No known incompatibilities. The latest part, 13510484, is the correct service replacement for all previous versions on the 2016-2021 Malibu.