P2729 on 2019-2020 GMC Sierra 1500: Causes, Symptoms, and Fixes

What's Unique About the 2019-2020 Gmc SIERRA 1500

For the 2019-2020 GMC Sierra 1500 and its platform-mate, the Chevrolet Silverado 1500, this code is not just a simple solenoid issue. General Motors has issued a Technical Service Bulletin (TSB #23-NA-018, which supersedes PIP5646D) that directly links P2729, along with P2724 and P2727, to a dangerous symptom: the rear wheels locking up at low speeds. The bulletin identifies the cause as an internal failure of the Transmission Control Module (TCM). A related Customer Satisfaction Program (N192272400) further specified the failure as an intermittent short circuit caused by wire bonds moving under high current and thermal load, making contact with adjacent wires inside the TCM. This makes the issue a specific, known manufacturing defect rather than a random component failure.

Diagnostic Flowchart

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

Symptoms You May Notice

• Rear wheels locking up at low speeds, especially after the vehicle has been sitting for a while (hot soak).
• Feeling as if the brakes were suddenly applied or the transmission was shifted into Park while moving.
• Symptom occurs after driving, then idling in park for 30 minutes to 4 hours, then shifting back to drive.
• Harsh or jerky shifting.
• Delayed gear engagement.
• Transmission may not have reverse after a lock-up event.
• Check Engine Light or Transmission Warning Lamp is illuminated.
• The issue may persist for several key cycles and may require the vehicle to be towed for service.

Most Likely Causes

1. Internal Failure of the Transmission Control Module (TCM) 🔴 High Probability → Shop Transmission Assembly A GM Technical Service Bulletin (#23-NA-018) and Customer Satisfaction Program (N192272400) explicitly identify an internal TCM failure as the cause. The failure is due to an intermittent short circuit from internal wire bonds moving under heat and load, contacting each other.
   How to confirm: Diagnosis by a professional technician is required. They will typically rule out other causes and then follow the TSB, which points directly to the TCM. The presence of wheel lock-up after a hot soak is a strong indicator. Per the TSB, technicians are advised NOT to clear DTCs as this can erase important diagnostic information.
   Typical fix: Replace the Transmission Control Module and program the new unit to the vehicle. The TSB specifies using part number 24043411 or its successor.
   Est. part cost: $600-$900
2. Poorly Seated TCM Electrical Connector 🟡 Medium Probability TSB #19-NA-228 notes that a variety of transmission codes, including P2729, can be set due to the main TCM connector not being fully seated or latched, leading to poor terminal contact.
   How to confirm: Visually inspect the large electrical connector at the TCM. TSB #19-NA-228 notes to look for the connector appearing 'crooked or high on one side'. A technician may need to disconnect and reconnect it to ensure a proper connection.
   Typical fix: Properly reseat and latch the TCM connector. No parts are typically required for this repair.
   Est. part cost: $0
3. Wiring Harness Damage ⚪ Low Probability GM TSB #21-NA-149 points out several areas where the engine and transmission wiring harness can chafe. Specific points of concern are contact with a sharp edge on the 'ECM/TCM bracket, driver side upper control arm, and/or shock tower'.
   How to confirm: A thorough visual inspection of the wiring harness is needed to find chafed or broken wires, focusing on the areas identified in TSB #21-NA-149.
   Typical fix: Repair the damaged section of the wiring harness following proper procedures and secure it to prevent future contact.
   Est. part cost: $5-$50 for repair materials
4. Faulty Pressure Control Solenoid 'E' ⚪ Low Probability → Shop Transmission Clutch Pressure Control Solenoid While the code directly names the solenoid, on this platform, the TCM is the much more likely culprit per GM's own service bulletins. However, a solenoid failure is still a possibility in cases where the primary symptom is not wheel lock-up.
   How to confirm: A technician can use a scan tool to command the solenoid on and off and check its resistance to see if it's within specification (typically 4.5-5.5 Ω for the 8L90 transmission).
   Typical fix: Replace the pressure control solenoid, which is located inside the transmission, often as part of the valve body.
   Est. part cost: $150-$300

Diagnosis Steps

1. Verify the vehicle and symptom. Confirm if the rear wheels have locked up at low speed, particularly after a hot soak.
2. Scan the TCM for diagnostic trouble codes. Note if P2729 is present with P2724 or P2727.
3. DO NOT clear DTCs or perform a Service Fast Learn (SFL) as this can erase important diagnostic information needed to confirm the known TCM issue.
4. Check for Technical Service Bulletins. TSB #23-NA-018 is highly relevant and points to a TCM failure. Also check TSB #19-NA-228 regarding the TCM connector and TSB #21-NA-149 for wiring chafe points.
5. Inspect the main TCM electrical connector (GM component ID K71) to ensure it is fully seated and latched correctly, looking for a 'crooked or high' appearance.
6. If the connector is secure and symptoms match TSB #23-NA-018, the recommended procedure is to replace the Transmission Control Module.
7. If symptoms do not match the TSB (no wheel lock-up), proceed with standard diagnostics: check transmission fluid level and condition, inspect wiring for damage per TSB #21-NA-149, and test the solenoid circuit.

Parts You'll Likely Need

• Transmission Control Module (TCM) (OEM #24043411) — This is the specific part identified by GM in service bulletin #23-NA-018 to fix the root cause of P2729 and the associated wheel lock-up issue on these trucks. Note that part numbers are often superseded.
  Trusted brands: ACDelco (OEM)
  OEM price range: $600-$900
  Aftermarket price range: N/A

Related Codes That Often Appear With This One

• P2724 — This code for Pressure Control Solenoid 'E' Stuck On is mentioned in the same TSB (#23-NA-018) and is also linked to the TCM failure.
• P2727 — This code for Pressure Control Solenoid 'E' Control Circuit Range/Performance is also cited in TSB #23-NA-018 as a related code caused by the faulty TCM.

Technical Service Bulletins (TSBs) & Recalls

• 23-NA-018 (replaces PIP5646D): Addresses rear wheel lock-up at low speeds and DTCs P2724, P2727, or P2729, identifying an internal TCM failure as the cause and recommending TCM replacement.
• 19-NA-228: Notes that P2729 and many other codes can be caused by a poorly seated TCM electrical connector.
• 21-NA-149: Describes potential wiring harness chafing issues on this platform that could lead to various electrical faults.
• N192272400: A 'Customer Satisfaction Program' bulletin detailing the TCM internal short-circuit and providing a remedy for affected vehicles.

Platform-Specific Known Issues

• A known issue, documented in TSB #23-NA-018, involves an internal TCM failure that can cause the rear wheels to lock up at low speeds after a hot soak.
• GM issued Customer Satisfaction Program N192272400 for this issue, which provided for a no-charge TCM replacement until June 30, 2022. Vehicles outside this program may still experience the failure.

Mechanic-Grade Diagnostic Values

• Pressure Control Solenoid Resistance (8L90/MQE Transmission) — expected: 4.5 - 5.5 Ω. Failure: A reading outside this range indicates a faulty solenoid.
• TCM Power Supply Fuse — expected: Continuity. Failure: An open fuse will cut all power to the TCM. Check fuse F49 in the engine compartment fuse block.

Scan Tool Commands That Help

• GDS2 (or equivalent professional scan tool): Transmission Service Fast Learn — This procedure allows the TCM to learn individual clutch apply pressures. It MUST be performed after replacing the TCM or valve body. However, TSB #23-NA-018 explicitly warns NOT to perform this procedure if diagnosing the wheel lock-up condition, as it can erase critical fault data.
• GDS2 / TIS2Web: K71 Transmission Control Module: Programming and Setup (SPS) — This is required any time the TCM is replaced. The new module must be programmed with the vehicle's specific VIN and calibration files from GM's Service Programming System (SPS). A Warranty Claim Code (WCC) is generated and must be recorded.
• GDS2 (or equivalent professional scan tool): Actuator Tests / Solenoid Command — Used to command a specific solenoid on and off to verify the TCM driver circuit is sending a signal. This helps differentiate between a wiring/solenoid fault and an internal TCM driver fault when the wheel lock-up TSB does not apply.

Wiring & Ground Locations

• K71 — The Transmission Control Module (TCM) is located in the front driver's side wheel well, mounted on a bracket behind the Engine Control Module (ECM). The fender liner must be removed for access.. This is the location of the primary failed component. It is also where the main connector is located, which should be inspected for being seated improperly per TSB 19-NA-228.
• Engine Compartment Fuse Block — Located on the driver's side of the engine bay, near the brake fluid reservoir.. This block contains fuse F49, which provides ignition power to the Transmission Control Module. A loss of power here will cause various TCM-related codes.

"I Checked Everything" — The Actual Cause

• For this electronic fault, the equivalent of a 'smoke test clean' scenario is when standard electrical checks of the solenoid and wiring do not reveal a fault. In the case of the 2019-2020 Sierra 1500 with wheel lock-up, GM TSB #23-NA-018 directs technicians to suspect an internal TCM failure even if the solenoid circuit tests normally, as the root cause is a known internal defect in the module itself.

OEM Part Supersession History

• 24043411 → 24070762 — Standard part revision by the manufacturer.
  Heads up: All replacement TCMs, regardless of part number, MUST be programmed with the vehicle's specific VIN and calibration files using GM's Service Programming System (SPS) to function.
• 24049790 → 24043411 — Standard part revision by the manufacturer.
• Multiple (24298475, 24296206, 24289415, etc.) → 24043411 — Part consolidation and revision.
  Heads up: While many part numbers may be physically interchangeable, the correct programming for the specific vehicle is critical. Always verify fitment by VIN.

Model Year Variations Within This Range

• 2019-2020: The P2729 code and associated wheel lock-up issue are specific to models equipped with the 8-speed (MQE) automatic transmission. In 2019, the 10-speed transmission was only offered with the 6.2L V8. For the 2020 model year, the 10-speed became more widely available, including on 5.3L V8 4WD models. A 2020 truck with a 10-speed transmission is not susceptible to this specific TCM failure mode.