P0746 on 2018-2024 Buick Enclave: Causes and Fixes for Transmission Issues

What's Unique About the 2018-2024 Buick ENCLAVE

For the 2018-2024 Buick Enclave, which uses a GM 9T65 9-speed transmission, code P0746 is frequently linked to a specific and severe internal mechanical failure. Manufacturer documents confirm that a primary cause is an out-of-round snap ring for the 1-2-3-4-5-6 clutch assembly. Specifically, TSBs identify the '(594) 1-2-3-4-5-6 Clutch Spring Retaining Ring' or the '(599) 1-2-3-4-5-6 Clutch Backing Plate Retaining Ring' as the defective parts. This part failing can cause the clutch pack to lose pressure, leading to a P0746 code and symptoms as severe as the vehicle not moving at all. This is a much more serious issue than a simple solenoid replacement.

Diagnostic Flowchart

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

Symptoms You May Notice

• Vehicle will not move when in Drive or Reverse. [Bulletin #PIE0720A]
• Slipping in and out of gear, or a slipping condition in forward ranges.
• Harsh, delayed, or erratic shifting.
• Check Engine Light or transmission warning light is on.
• Transmission may feel like it's stuck in one gear (limp mode).
• Increased fuel consumption.

Most Likely Causes

1. 1-2-3-4-5-6 Clutch Snap Ring Failure 🔴 High Probability GM has issued Technical Service Bulletins (TSBs) specifically identifying that out-of-round snap rings can pop out of their grooves in the 9T65 transmission, causing this code.
   How to confirm: This requires transmission disassembly and inspection by a qualified technician. The TSB notes that this issue is suspected in transmissions with a build date between October 1, 2023, and April 22, 2024 (Julian date between 23274 and 24113). If the code resets on a short test drive or the vehicle slips, the TSB recommends disassembly and inspection.
   Typical fix: The transmission must be removed and disassembled to replace the faulty snap ring and inspect for any related damage to the clutch pack or other internal components. The warranty labor operation for this repair is coded as 8465262.
   Est. part cost: $50-$200 for internal seals, gaskets, and the snap ring itself.
2. Low or Dirty Transmission Fluid 🟡 Medium Probability
   How to confirm: Check the transmission fluid level and condition. The 2018+ Enclave does not have a traditional dipstick; the level must be checked via a plug on the side of the transmission case while the vehicle is running and at a specific temperature (85–95°C or 185–203°F). Dark, burnt, or contaminated fluid indicates a problem.
   Typical fix: Perform a transmission fluid drain and fill using the correct specification fluid (ACDelco DEXRON VI or equivalent). If the fluid is very dirty, a full flush may be recommended by a professional.
   Est. part cost: $100-$200 for fluid.
3. Failed Pressure Control Solenoid ('A') ⚪ Low Probability While the code directly names the solenoid, on this platform it is often a symptom of the mechanical snap ring failure rather than the root cause. The TSB explicitly warns against replacing the solenoid body for this issue.
   How to confirm: A technician can use a high-end scan tool to command the solenoid on and off and monitor pressure readings. The solenoid's electrical resistance can also be tested. This part is located inside the transmission, attached to the valve body.
   Typical fix: Replace the pressure control solenoid. This requires removing the transmission pan and valve body. However, this is NOT the recommended fix if the snap ring issue is suspected.
   Est. part cost: $70-$150

Rare But Worth Checking

• Faulty Transmission Valve Body: The valve body is the hydraulic brain of the transmission. A stuck valve or clogged passage can mimic a failed solenoid. However, GM TSBs for the snap ring issue specifically warn *not* to replace the valve body as it is not the cause of this specific failure pattern.
• Failed Transmission Control Module (TCM): In rare cases, the computer that controls the transmission can fail, but all other more common causes should be ruled out first.
• Wiring Issues: An open or short in the wiring to the pressure control solenoid can cause the code to set. This should be checked before condemning internal components, unless the vehicle falls within the TSB date range for the snap ring issue.

Diagnosis Steps

1. Check the transmission fluid level and condition. This must be done by a professional as there is no dipstick and requires the vehicle to be level and at a specific temperature (85-95°C / 185-203°F).
2. Scan the TCM for all stored trouble codes. Note if P0747 is also present.
3. Check the transmission build date. If it falls between October 1, 2023, and April 22, 2024 (Julian dates 23274-24113), the snap ring issue is highly probable per TSB PIP5974A/E.
4. Perform a line pressure test to see if the transmission is capable of building hydraulic pressure. A reading below 345 kPa (50 psi) indicates an internal problem.
5. If pressure is low and fluid level is correct, the next step is to suspect an internal mechanical fault.
6. Given the high probability of the snap ring issue on these vehicles, the recommended procedure is transmission removal and inspection, as outlined in GM service literature and TSBs.

Parts You'll Likely Need

• Transmission 1-2-3-4-5-6 Clutch Spring/Backing Plate Retaining Ring (OEM #Part of internal kit; specific updated ring number not published in TSBs. A general GM snap ring for this clutch is P/N 24267707, but verification for this specific application is required.) — This is the most likely root cause of the problem according to manufacturer TSBs PIP5974E and PIP5974A.
  Trusted brands: ACDelco, GM Genuine
  OEM price range: $10-$30
  Aftermarket price range: $5-$20
• Transmission Gasket and Seal Kit — Required for any internal transmission repair to properly reseal the unit.
  Trusted brands: ACDelco
  OEM price range: $150-$300
  Aftermarket price range: $100-$200
• Automatic Transmission Fluid (OEM #ACDelco DEXRON VI) — The transmission must be refilled with new fluid after the repair.
  Trusted brands: ACDelco DEXRON VI
  OEM price range: $15-$25 per quart
  Aftermarket price range: $10-$18 per quart

Related Codes That Often Appear With This One

• P0747 — This code means 'Pressure Control Solenoid 'A' Stuck On'. P0746 and P0747 are often seen together or alternately because they both relate to the same hydraulic circuit and mechanical failure (the snap ring), causing erratic pressure control. A mechanical failure like a dislodged snap ring can cause a loss of pressure ('Stuck Off') or prevent pressure from releasing ('Stuck On') depending on the exact state of the failure.

Technical Service Bulletins (TSBs) & Recalls

• PIP5974E (Dec 4, 2024): Communicates that an out-of-round 1-2-3-4-5-6 snap ring can cause P0746 or P0747 and lists affected models.
• PIP5974A (May 6, 2024): Earlier version of the TSB providing specific Julian date ranges for the faulty transmissions and explicitly warning against replacing the valve body or solenoids.
• PIE0720A / PIE0720: Documents cases of vehicles with P0746/P0747 that will not move in Drive, Neutral, or Reverse.

Platform-Specific Known Issues

• A known issue documented in TSB PIP5974E involves the 1-2-3-4-5-6 clutch snap ring being out of round, causing it to pop out of its groove. This leads to a loss of hydraulic pressure for that clutch pack, triggering code P0746 and potentially a no-move condition.
• This failure is prominent enough that GM has identified a specific range of transmission build dates (Oct 2023 - Apr 2024) that are highly susceptible.

Mechanic-Grade Diagnostic Values

• Transmission Line Pressure at Idle — expected: Greater than 345 kPa (50 psi). Failure: Pressure below 345 kPa (50 psi) indicates a potential internal leak, pump issue, or the snap ring failure.
• Transmission Fluid Temperature for Level Check — expected: 85–95°C (185–203°F). Failure: Checking the fluid level outside this temperature range will result in an inaccurate reading (under-filled if too hot, over-filled if too cold).

Scan Tool Commands That Help

• GDS2 (GM Dealer Scan Tool): Control Function - Shift Commands — To isolate the fault between an electronic command issue and an internal mechanical/hydraulic failure. If the transmission shifts into each gear when commanded by GDS2, the problem is likely an input/command concern. If it fails to shift as commanded, the fault is internal to the transmission.

OEM Part Supersession History

• 24293253, 24043757 → 24045659 — Standard part revision and consolidation.
  Heads up: This is for the complete valve body assembly. TSB PIP5974A/E specifically warns *not* to replace the valve body for the common snap ring issue, as it is not the cause.
• Unknown (original factory part) → 24267707 (and associated clutch pack components) — The original snap rings were found to be 'out of round', leading to them popping out of the groove. The replacement parts are intended to correct this manufacturing defect.
  Heads up: When replacing the snap ring, GM TSB PIP5974A/E requires replacing the entire 1-2-3-4-5-6 clutch pack assembly, including pistons, seals, and plates, not just the ring itself. Special tools (DT47797 and DT47797-2) are required to properly seat the new snap ring, which makes a loud 'popping' noise when installed correctly.

Model Year Variations Within This Range

• 2023-2024: Transmissions with a build date between October 1, 2023, and April 22, 2024 (Julian dates 23274-24113) are highly susceptible to the 1-2-3-4-5-6 clutch snap ring failure due to a batch of 'out of round' parts. While the failure can occur on other years, it is most probable on vehicles from this specific period.