P2798 on 2021-2023 Chevrolet Bolt EV: Transmission Fluid Pump Fixes

What's Unique About the 2021-2023 Chevrolet BOLT EV

Unlike a traditional car, the Bolt EV's 'transmission' is a single-speed electric drive unit. 🎬 See: How to service the Bolt EV drive unit fluid The fluid pump in question is not for shifting gears but for thermal management of the drive unit. A GM Technical Service Bulletin (TSB #21-NA-148) for this exact vehicle range points to a known manufacturing defect (an out-of-spec soldering process) in a batch of these pumps, making pump failure a more common issue than on other vehicles. This issue is so prevalent that many owners report it occurring on brand new vehicles with very low mileage.

Diagnostic Flowchart

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

Symptoms You May Notice

• "Propulsion Power is Reduced" message on the Driver Information Center (DIC).
• "Service Vehicle Soon" or Check Engine Light illuminated.
• Vehicle speed limited, sometimes to as low as 32 mph (51 km/h).
• OnStar diagnostic report mentioning an issue with the "Auxiliary Transmission Pump System".

Most Likely Causes

1. Failed Electric Transmission Fluid Pump 🔴 High Probability → Shop Transmission Assembly TSB #21-NA-148 explicitly identifies a 'part quality spill' due to an improper soldering process in the pump's internal electronics for 2021-2023 models, including the Bolt EUV. This is a known manufacturing defect.
   How to confirm: A technician will use a scan tool to verify DTC P2798 or the related P2797. Following the TSB, if the code is present, the diagnosis is to replace the pump assembly.
   Typical fix: Replace the electric transmission fluid pump assembly. The pump is not internally serviceable. This repair should be covered under the vehicle's powertrain warranty.
   Est. part cost: $132-$215
2. Damaged Wiring or Connectors ⚪ Low Probability An earlier TSB for the 2017 Bolt (17-NA-030) noted that the pump's wiring harness could be damaged by chafing behind the left front wheelhouse liner, causing a short. While the primary issue for 2021-2023 models is the pump itself, a wiring fault is still a possibility, though less likely.
   How to confirm: Visually inspect the wiring harness leading to the pump for chafing, breaks, or corrosion, particularly behind the driver's side wheel liner. Test for continuity and proper voltage at the pump connector.
   Typical fix: Repair the damaged section of the wiring harness and use protective tape to prevent future contact.
   Est. part cost: $5-$20 for repair materials
3. Control Module Issue Very Low Probability
   How to confirm: This would only be considered after both the pump and wiring have been confirmed to be in good working order. A technician would diagnose the control module by checking the output signal with an oscilloscope.
   Typical fix: Reprogramming or replacing the responsible control module 🎬 Watch: Challenges when replacing the transmission range control module (e.g., the Drive Motor Generator Power Inverter Control Module).
   Est. part cost: $600-$900 for a new module

Diagnosis Steps

1. Verify the code with an OBD-II scanner. P2798 or P2797 will be present.
2. Check for relevant Technical Service Bulletins. TSB #21-NA-148 directly addresses this code for this vehicle and its platform mate, the Bolt EUV.
3. According to the TSB, if DTC P2797, P2798, or P0C2D is set 🎬 Watch: Diagnostic overview of the auxiliary transmission pump failure, the corrective action is to replace the transmission fluid pump.
4. While not the primary cause for these model years, it is still best practice to inspect the wiring harness and connector for any signs of physical damage or corrosion, as outlined in the older TSB 17-NA-030.
5. The pump is located on the driver's side of the electric drive unit.
6. The repair must be performed by a certified EV technician due to the high-voltage system.

Parts You'll Likely Need

• Electric Transmission Fluid Pump (OEM #25204070) — This is the component identified as faulty in TSB #21-NA-148 due to a manufacturing defect. A March 2024 revision of the TSB updated the part number to 25204070, superseding previous numbers like 25200558 and 24049831.
  Trusted brands: ACDelco / GM Genuine Parts
  OEM price range: $132-$215

Related Codes That Often Appear With This One

• P2797 — This code for 'Auxiliary Transmission Fluid Pump Control Circuit Range/Performance' is part of the same diagnostic group and is explicitly mentioned in TSB #21-NA-148 as being caused by the same faulty pump.
• P0C2D — This code for 'Drive Motor Inverter Temperature Sensor 'C' Circuit' is also listed in TSB #21-NA-148, as a failing pump leads to inadequate cooling of the drive unit, which can trigger temperature-related faults.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #21-NA-148: (Revised March 2024) Provides a diagnostic aid for DTCs P2797, P2798, or P0C2D. It identifies a quality issue with the transmission fluid pump due to an out-of-spec soldering process and recommends its replacement. It also updates the causal part number to 25204070.
• Bulletin #17-NA-030: While for the 2017 model year, it establishes a history of wiring harness chafing behind the driver's side wheel liner causing these codes and advises checking wiring before replacing the pump.

Platform-Specific Known Issues

• A known manufacturing defect in the transmission fluid pump's soldering process affects 2021-2023 models, as documented in TSB #21-NA-148.
• Many owners have experienced this failure at extremely low mileage (e.g., under 200 miles), indicating a widespread quality control issue with a batch of parts.
• Owners have reported significant delays in repair due to the replacement pump being on backorder, sometimes waiting weeks or months for the part to arrive.
• In some cases of prolonged repair times (over 30 days), owners have pursued lemon law claims, leading to vehicle buybacks by GM.

Mechanic-Grade Diagnostic Values

• Voltage at the transmission fluid pump's power terminal (with ignition ON) — expected: 9V - 12V. Failure: A reading below 9V, especially below 5V, indicates a circuit issue upstream of the pump.
• Control module output pin for the pump — expected: 60% - 80% duty cycle (when commanded ON). Failure: An incorrect or absent PWM signal when the pump should be active points to a control module or wiring issue.
• Direct pump motor test — expected: The motor should spin smoothly.. Failure: If the motor does not spin when a known-good 12V source is applied directly to its terminals, the pump itself has an internal mechanical or motor failure.

Scan Tool Commands That Help

• GM GDS2 (or equivalent professional scan tool): Pump Activation Test / Output Control — This bidirectional command is used to manually turn the auxiliary transmission fluid pump on and off. It helps a technician verify if the pump motor runs, listen for audible noise (whine), and confirm if the control module and wiring are capable of commanding the pump.

Wiring & Ground Locations

• G5 Transmission Fluid Pump Location — Attached to the driver's side of the electric drive unit (transmission). It is accessible after removing the front left wheel and the wheelhouse liner.. This is the physical location of the component that most commonly fails and sets DTC P2798.
• G5 Pump Wiring Harness Chafe Point — The wiring harness leading to the pump connector, specifically in the area behind the left front wheelhouse liner.. TSB 17-NA-030 for the 2017 model identified that this harness can chafe against chassis components, causing a short to ground and setting this code. While less common on 2021-2023 models, it is a critical inspection point before replacing the pump.
• Jump Start Negative Ground Post — A dedicated metal post in the under-hood area, separate from the 12V battery, used for jump-starting.. This provides a known-good, easily accessible chassis ground point for performing voltage and continuity tests on the pump circuit.

Real Owner Repair Stories

• Reddit user on r/BoltEV (2023 Bolt EUV) — Intermittent 'Propulsion Power is Reduced' message, occurring once every couple of months. The service light comes on but often turns off by the next day.
  ❌ Tried (didn't work) Replacing the auxiliary transmission fluid pump., A second, unspecified repair performed by a different dealer.
  ✅ What actually fixed it The issue was not resolved. The owner had the pump replaced, but the intermittent fault continued to occur across three different dealer visits. This suggests a rare underlying issue beyond the pump itself, such as a subtle wiring fault or a control module problem that standard diagnostics did not catch.

When the Usual Fixes Don't Work

• While TSB #21-NA-148 points to a defective transmission fluid pump as the definitive cause for P2798, there is at least one documented owner case where replacing the pump did not resolve the issue. The owner of a 2023 EUV continued to experience intermittent 'Propulsion Power is Reduced' warnings even after the pump was replaced by a dealer. This indicates that in rare instances, the fault may lie elsewhere, such as in the wiring harness or a control module, and that the TSB's guidance to simply replace the pump is not a guaranteed fix in 100% of cases.

OEM Part Supersession History

• 25200558 → 25204070 — Part update to address the known quality issue.
  Heads up: The March 2024 revision of TSB 21-NA-148 officially changed the causal part number to 25204070.
• 25204070 → 25207705 — Unknown, likely a further revision or supplier change.
  Heads up: While the TSB points to 25204070 as the latest number, at least one owner reported a dealer installing part number 25207705 to fix the issue in 2024. Technicians should be aware that multiple 'latest' part numbers may be in circulation.

Model Year Variations Within This Range

• 2023: TSB 21-NA-148 was officially revised on July 28, 2023, to add the 2023 model year to its scope. Prior to this date, a technician looking up the TSB might have incorrectly concluded it only applied to 2021-2022 models.