P2797 on 2009-2013 GMC Yukon Denali Hybrid: Aux Pump Circuit Causes and Fixes

What's Unique About the 2009-2013 Gmc YUKON DENALI

This code is specific to the 2-Mode Hybrid system (transmission model 2ML70, RPO M99) used in the Yukon Denali and its siblings like the Chevrolet Tahoe, Cadillac Escalade, and GMC/Chevy pickups. Unlike a conventional transmission, this system relies on a 12V electric auxiliary pump to keep the transmission pressurized and ready to go when the engine is off. The initial diagnostic impulse for this code was often to replace the pump, but GM later identified that wiring issues were the more common culprit, leading to a specific Technical Service Bulletin (TSB PIP4873A) to guide technicians to check wiring first.

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 or "Service Hybrid System" message is illuminated.
• Vehicle's Auto-Stop feature is inoperative.
• Jerking, bumping, or surging sensation when the vehicle switches between electric and gasoline engine power, or during low-speed braking.
• Hesitation, lull, or pauses in acceleration at low speeds, sometimes followed by a kick as the clutch grabs.
• Harsh or delayed gear shifts.
• Audible clicking noises or changes in electric motor sounds from the transmission area.

Most Likely Causes

1. Damaged or Corroded Wiring Harness 🔴 High Probability The wiring harness between the Hybrid Powertrain Control Module (HPCM) and the auxiliary transmission fluid pump is susceptible to chafing, corrosion, or loose pins at the connectors. This is the most common cause identified by GM in TSB PIP4873A. Forum users report that high current can overheat pins in the connectors, leading to a poor connection over time, especially on 2009 models before the connectors were updated.
   How to confirm: Follow the diagnostic steps in TSB PIP4873A. Visually inspect the entire wiring harness for damage. A common failure point is near the connectors under the battery. Use a multimeter to test for continuity and shorts on the control, voltage, and ground circuits. Wiggling the harness while monitoring scan tool data can help identify intermittent faults.
   Typical fix: Repair the damaged section of the wiring harness using solder and heat-shrink tubing or replace the affected connector pigtail. In some cases, cleaning the connector pins and ensuring a tight fit is all that is needed. GM also offers replacement harness sections (e.g., part number 24259588).
   Est. part cost: $10-$75
2. Failed Auxiliary Transmission Fluid Pump Control Module 🟡 Medium Probability The control module (part number 24261817) that commands the pump can fail internally. This is considered the next most likely cause after wiring issues have been ruled out. Some TSBs suggest replacing the module if it has an older date code (e.g., 089-11-XXXX or older) and the issue is intermittent.
   How to confirm: This is typically diagnosed by exclusion. If the wiring and pump are known to be good, the control module becomes the primary suspect. A scan tool can be used to monitor the module's fault status parameters.
   Typical fix: Replace the auxiliary transmission fluid pump control module. This part may require programming by a dealer. The part supersedes several older numbers including 29543906, 29546431, and 29547550.
   Est. part cost: $120-$250
3. Failed Auxiliary Transmission Fluid Pump ⚪ Low Probability While less common than wiring or module issues for this specific code, the electric pump can fail internally due to wear. TSB PIP4873A explicitly warns against replacing the pump as a first step.
   How to confirm: If the wiring harness and control module are confirmed to be in good condition, and the pump receives the correct voltage but does not operate or makes excessive noise, the pump itself is likely faulty. A scan tool can command the pump to run and compare commanded vs. actual speed.
   Typical fix: Replace the auxiliary transmission fluid pump. This is an involved repair that requires partial disassembly of the transmission.
   Est. part cost: $600-$950

Diagnosis Steps

1. Scan the vehicle's computers for all stored Diagnostic Trouble Codes (DTCs). Note if P2797 is present with P0C2B or P0AC4.
2. Obtain and review GM Technical Service Bulletin #PIP4873A, which directly addresses this issue for your vehicle.
3. DO NOT replace the auxiliary transmission fluid pump or control module initially. First, perform a thorough visual inspection of the wiring harness between the Hybrid Powertrain Control Module (HPCM) and the auxiliary pump control module.
4. Specifically check connectors for corrosion, backed-out pins, or signs of overheating. On 2009 models, the connectors under the battery are a known trouble spot.
5. Using a digital multimeter, test the pump's control circuit for 11-13V at PIM connector X1, terminal 3 with the ignition on.
6. If a wiring fault is found, repair the damaged section securely using solder and heat-shrink tubing or an appropriate pigtail connector.
7. If the wiring and connectors are confirmed to be in perfect condition, diagnose the control module. Check the date code on the module; older modules are more prone to failure.
8. As a final step if wiring and the module are good, test the pump itself using a scan tool to command operation and verify its speed and performance.
9. Clear the DTCs and perform a test drive, ensuring the vehicle enters Auto-Stop mode to confirm the repair was successful.

Parts You'll Likely Need

• Wiring Repair Supplies — The most common fix is repairing the existing wiring harness, which requires basic electrical supplies or a connector pigtail.
  Aftermarket price range: $10-$50
• Auxiliary Transmission Fluid Pump Control Module (OEM #24261817) — This is the second most likely part to fail after wiring. It may require dealer programming. It supersedes multiple older part numbers.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $120-$185
• Auxiliary Transmission Fluid Pump (OEM #19207983) — This part is replaced only if it is confirmed to have failed after wiring and module issues have been ruled out.
  Trusted brands: ACDelco
  OEM price range: $600-$950
  Aftermarket price range: $400-$700

Related Codes That Often Appear With This One

• P0C2B — This code, for 'Auxiliary Transmission Fluid Pump Control Module Feedback Signal', is often set alongside P2797 because both relate to the communication and performance of the same pump system. TSB PIP4873A mentions both codes together and states P0C2B is not likely caused by the pump itself.
• P0AC4 — This code indicates that the Hybrid Powertrain Control Module has requested the Malfunction Indicator Lamp (MIL) to be turned on. It's a general code that accompanies more specific fault codes like P2797 to illuminate the Check Engine Light.

Technical Service Bulletins (TSBs) & Recalls

• PIP4873A: States that for DTC P2797 with or without P0C2B, technicians should inspect the wiring between the HPCM and the auxiliary pump control module and should not replace the pump as a first step. It points to wiring or the module as the likely cause.
• 10-07-30-009: Details the connector differences between 2008-2009 and 2010+ models for the auxiliary pump and control module, specifying required adapter harnesses when using newer parts on older trucks.

Platform-Specific Known Issues

• A known issue on this platform is the guidance in TSB #PIP4873A, which states that DTC P2797 (with or without P0C2B) is often caused by a wiring issue and that the auxiliary transmission fluid pump should not be replaced as the first step.
• Owners on forums frequently report a distinct 'bump' or 'jerk' during the transition to or from Auto-Stop, which is a classic symptom of this P2797 fault.
• The connectors for the pump module on 2009 models were prone to overheating; an updated design was used in later years. Some owners have had success simply by cleaning and re-seating these connectors.

Mechanic-Grade Diagnostic Values

• Commanded vs. Actual Pump Speed Difference — expected: Less than 500 RPM difference.. Failure: A difference greater than 500 RPM for 4 seconds will set DTC P2797.
• Auxiliary Oil Pump Control Circuit Voltage — expected: 11-13 Volts. Failure: Voltage less than 11V indicates an open or short to ground in the control circuit.
• Auxiliary Pump Motor Current at Start-up — expected: Less than 20 Amps. Failure: Current draw of more than 20 Amps indicates a fault, likely a seized pump motor.

Hidden / Shadow Codes Worth Checking

• N/A: The Auxiliary Transmission Fluid Pump (ATFP) control module does not store its own DTCs. All diagnostic status, including faults that trigger P2797, are reported directly to the Hybrid Powertrain Control Module (HPCM) in the current ignition cycle. Therefore, all relevant codes are visible on a standard scan of the HPCM. (see via GM Tech 2 or GDS2 scan of the HPCM.)

Scan Tool Commands That Help

• GM Tech 2 / GDS2: Auxiliary Transmission Fluid Pump Speed Control — Use this bidirectional command to manually operate the pump. Command the pump speed to 50% and observe the 'Aux. Trans. Fluid Pump Fault Status' parameters. This directly tests the functionality of the control module, wiring, and pump motor, separating it from the HPCM's automated commands.

Wiring & Ground Locations

• Pump/Module Connectors — Underneath the main 12V vehicle battery in the engine compartment.. This is a known high-failure area, especially on 2009 models. The high current draw can overheat connector pins, causing a poor connection that triggers P2797. Cleaning and re-seating these connectors often resolves the issue.
• G305 — Under the vehicle to the rear of the left (driver's side) B-pillar, located at the third body mount on the frame.. This is a primary body ground point specified for Hybrid (RPO HP2) models. A poor connection here can cause a variety of difficult-to-diagnose electrical issues with hybrid-specific components like the auxiliary pump module.
• PIM Connector X1, Pin 3 — This is a specific pin on the Power Inverter Module (PIM) connector.. This is the specific pin for the 'Trans. Aux. Oil Pump Control' circuit. Service manual diagnostics require testing for 11-13V at this pin to verify the integrity of the control signal wiring from the HPCM.

Real Owner Repair Stories

• TahoeYukonForum.com user 'lt1gmc' (2009 model) — Classic 'bump/jerk' sensation, accompanied by codes P2797, P0C2B, and P0AC4.
  ❌ Tried (didn't work) The user dealt with the intermittent issue for 15,000 miles by repeatedly unplugging and replugging the connectors.
  ✅ What actually fixed it The final fix was to thoroughly clean the pins on the auxiliary pump and module connectors located under the battery. The user noted that high current had likely overheated a pin, causing a bad connection, and that GM updated these plugs in 2010.

OEM Part Supersession History

• 29543906, 29546431, 29546469, 29546636, 29547550 → 24261817 — Part consolidation and design updates.
  Heads up: The current module (24261817) uses connectors from the 2010+ design. When installing on a 2008-2009 vehicle, adapter harnesses are required. Specifically, connector p/n 24259589 and 24259590 are needed to connect the new module to the old vehicle harness.
• Original 2008-2009 pump → 19207983 — Connector design update for 2010 model year.
  Heads up: The current service pump (19207983) has the 2010+ style connector. If installing this pump on a 2008-2009 vehicle that still has its original control module, adapter harness p/n 24259588 is required.

Model Year Variations Within This Range

• 2009 (and 2008): The electrical connectors for the auxiliary transmission fluid pump and its control module are a known weak point, prone to overheating from high current. This was addressed with an updated connector design starting with the 2010 model year. As a result, replacing the pump or module on a 2009 model with current service parts requires specific adapter harnesses.