P0746 on 2020-2024 Cadillac XT6: Pressure Control Solenoid Causes and Fixes

What's Unique About the 2020-2024 Cadillac XT6

For the Cadillac XT6 and other GM vehicles with the 9T-series transmission (specifically the 9T65, RPO code M3W), P0746 is a well-documented and serious issue. GM has issued multiple Technical Service Bulletins (TSBs) that point directly to a significant internal mechanical flaw. The most critical issue is an out-of-round 1-2-3-4-5-6 clutch snap ring 🎬 Watch: A detailed explanation of the snap ring failure and shudder. that can pop out of its groove, leading to clutch failure and triggering this code. TSB PIP5974E specifically identifies the '(594) 1-2-3-4-5-6 Clutch Spring Retaining Ring' or '(599) 1-2-3-4-5-6 Clutch Backing Plate Retaining Ring' as the defective parts. This means that simply replacing the valve body or the solenoid is often the wrong repair and will not fix the root cause, which is a major mechanical failure requiring transmission disassembly.

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, or will only creep forward with high throttle input.
🎬 See a diagnostic teardown of a transmission with no movement.
• Harsh, delayed, or erratic shifting, particularly a hard shift between 2nd and 3rd gear.
• Transmission gets stuck in one gear (limp mode).
• Slipping in and out of gear, with engine RPMs flaring without an increase in speed.
• Illuminated Check Engine Light.
• Increased fuel consumption.
• Transmission overheating.
• Flashing 'D' on the PRNDL (gear selector) display.

Most Likely Causes

1. Internal Transmission Mechanical Failure (Out-of-Round Snap Ring) 🔴 High Probability → Shop Transmission Assembly GM TSB #PIP5974E specifically identifies an out-of-round snap ring for the 1-2-3-4-5-6 clutch as a known defect on this transmission series. The ring can pop out of its groove, causing a loss of clutch pressure. TSB PIP5974A further specifies that transmissions built between Julian dates 23 274 and 24 113 (October 1, 2023 - April 22, 2024) are highly susceptible.
   How to confirm: Professional diagnosis is required. A technician should check the transmission's Julian build date. If it falls in the affected range, this is the prime suspect. Dropping the transmission pan and finding metal fragments (pieces of the snap ring or clutch material) is a strong indicator. Ultimate confirmation requires transmission disassembly to visually inspect the clutch pack and snap rings.
   Typical fix: The transmission must be removed and disassembled to replace the faulty snap ring and any other damaged clutch components. TSBs indicate that the '(590) 1-Reverse and 1-2-3-4-5-6 Clutch Piston Housing' must also be replaced along with the updated snap ring. Due to the metal debris contamination, the torque converter and valve body are often damaged and require replacement as well. A complete transmission rebuild or replacement is often the most practical solution.
   Est. part cost: $2000-$6000
2. Faulty Transmission Valve Body or Solenoid 🟡 Medium Probability → Shop Transmission Valve Body While a mechanical failure is more likely, the solenoid itself or the valve body it's housed in can fail. However, TSB #PIP5974E and PIP5974A specifically warn against replacing the valve body alone if the snap ring issue is the true cause, as it will not solve the problem and will lead to a repeat failure.
   How to confirm: A technician can command the solenoid with a high-level scan tool and monitor pressure readings. A line pressure test can check for internal leaks. An inspection of the valve body for debris or stuck valves is also necessary, but finding debris often points back to the primary snap ring failure.
   Typical fix: Replacement of the pressure control solenoid or the entire transmission control valve body assembly. This should only be done after the snap ring failure has been definitively ruled out.
   Est. part cost: $400-$1200
3. Low or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly This is a potential cause for any automatic transmission, but less likely to be the root cause on the XT6 given the known mechanical issues. Contaminated fluid with metal shavings is typically a symptom of the snap ring failure, not the cause itself.
   How to confirm: Check the transmission fluid level and condition according to the manufacturer's procedure. The XT6 does not have a traditional dipstick, so this must be done by a professional via the fluid level plug on the side of the transmission case. 🎬 Watch: How to properly check and change your 9T65 transmission fluid.
   Typical fix: Perform a transmission fluid and filter change using the correct ACDelco DEXRON VI fluid. If the fluid is low, the source of the leak must be identified and repaired. If the fluid is full of metal, this confirms a major internal failure.
   Est. part cost: $150-$350

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly A TCM failure is rare but possible. It should only be considered after all mechanical and hydraulic issues have been definitively ruled out.
• Wiring or Connector Issues: An open or short in the wiring to the pressure control solenoid can mimic a failed solenoid. A visual inspection and continuity test of the harness can confirm this.

Diagnosis Steps

1. Verify the P0746 code is present using a professional OBD-II scanner.
2. Check for any other related transmission codes, especially P0747.
3. Check the transmission's Julian build date against TSB #PIP5974A (dates between 23 274 and 24 113) to see if it's in the high-risk group.
4. Check the transmission fluid level and condition via the fluid level plug. This must be done by a technician as there is no dipstick. Note any dark, burnt fluid or metallic sheen.
5. Inspect the transmission pan for excessive metal debris (snap ring fragments), which would confirm a severe mechanical failure.
6. Perform a line pressure test to see if the transmission is capable of building adequate pressure. Readings below 55-60 PSI at idle can indicate a major internal leak.
7. Given the high probability of the snap ring issue described in TSB #PIP5974E, the next step is typically transmission removal and inspection by a qualified transmission specialist.
8. If no mechanical fault is found, test the solenoid circuit, wiring, and the solenoid itself before condemning the TCM.

Parts You'll Likely Need

• Transmission Assembly (OEM #24296141 (Verify with VIN)) — Due to the high likelihood of a severe internal mechanical failure (snap ring), a complete remanufactured or new transmission is often the most reliable and time-effective repair.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $4000-$6000
  Aftermarket price range: $3000-$5000
• Transmission Rebuild Kit (including snap rings and clutches) — If a specialist rebuilds the existing transmission, this kit contains the necessary seals, gaskets, clutches, and updated snap rings to correct the fault. The 1-2-3-4-5-6 Clutch Piston Housing (part 590) must also be replaced.
  Trusted brands: ACDelco
  OEM price range: $500-$900
  Aftermarket price range: $400-$700
• Transmission Control Valve Body — This is a potential cause if the primary mechanical failure is ruled out. It is often replaced during a rebuild as a preventative measure against contamination from metal debris. TSBs warn against replacing this part as a standalone fix for P0746.

Related Codes That Often Appear With This One

• P0747 — P0747 is for 'Pressure Control Solenoid 'A' Stuck On'. The same underlying mechanical failure (like the snap ring) can cause either a 'Stuck Off' (P0746) or 'Stuck On' (P0747) condition depending on how the failure mode presents itself to the TCM. GM TSBs list these codes together as pointing to the same root cause.
• P0700 — P0700 is a generic code that simply means the Transmission Control Module (TCM) has stored a fault. It will almost always be present alongside a more specific code like P0746 to illuminate the Check Engine Light.

Technical Service Bulletins (TSBs) & Recalls

• PIP5974E: Communicates possible transmission 1-2-3-4-5-6 snap rings out of round causing code p0746 or p0747.
• PIP5974A: Updates the snap ring issue, identifying a specific range of transmission build dates (Oct 2023 - Apr 2024) as highly susceptible and warns against replacing the valve body.
• PIE0720A: Ends the need to gather further information from technicians in regards to Vehicle Will Not Move When in Drive, Neutral and/or Reverse and DTCs P0746, P0747 Set.
• PIE0720: A request to perform a check list and contact an engineer regarding a no-move condition with DTCs P0746, P0747 set.
• 20-NA-136: Details a past pilot program for low-mileage vehicles that mandated full transmission replacement instead of internal repairs for codes like P0746, and now provides an enhanced diagnostic strategy based on learnings from that program.

Platform-Specific Known Issues

• TSB #PIP5974E: Documents that an out-of-round 1-2-3-4-5-6 clutch snap ring can come out of its groove, causing DTC P0746 or P0747 and potentially a no-move condition. It specifically warns against just replacing the valve body for this issue.
• TSB #PIP5974A: An update to the previous TSB which specifies a high-risk range of transmission build dates (Oct 2023 - Apr 2024) that are particularly susceptible to the snap ring failure.
• TSB #PIE0720A / #PIE0720: These bulletins were created to gather information from technicians regarding a 'Vehicle Will Not Move' condition associated with codes P0746 and P0747, highlighting the severity and prevalence of the issue.
• TSB #20-NA-136: This bulletin ended a pilot program where dealers were instructed to replace the entire 9T65 transmission for any internal fault on low-mileage vehicles, rather than attempting a repair. This underscores the complexity and high failure rate of initial repairs.

Mechanic-Grade Diagnostic Values

• Transmission Line Pressure at Idle — expected: Greater than 345 kPa (50 psi). Failure: Pressure below 50 psi indicates a major internal hydraulic leak, consistent with the snap ring failure.
• Transmission Fluid Temperature (TFT) for Fluid Level Check — expected: 85–95°C (185–203°F). Failure: Checking the fluid level outside this temperature range will result in an inaccurate under-filled or over-filled reading.
• Pressure Control Solenoid Resistance — expected: ~5.1 Ohms at 68°F (20°C). Failure: A reading significantly higher or lower than the specification, or an open circuit, indicates a failed solenoid coil.

Scan Tool Commands That Help

• GDS2 (GM Techline Connect): Transmission Adaptive Values Learn — After any transmission repair, such as replacing the valve body or the entire assembly, to clear old learned values and force the TCM to relearn shift pressures in the service bay.
• GDS2 (GM Techline Connect): Active Test - Shift Transmission — To determine if the fault is with the transmission's internal hydraulics or an external input/command. If the transmission shifts correctly when commanded by the scan tool, the problem is more likely an input (sensor, wiring) rather than an internal mechanical failure.
• GDS2 (GM Techline Connect): Monitor Transmission Input Speed Sensor (ISS) RPM — During 'garage shifts' (P to R, N to D) to confirm if a gear is engaging. A delay or failure for the ISS RPM to change as expected can indicate a hydraulic apply problem related to P0746.

Wiring & Ground Locations

• Transmission Harness Chafe Point 1 — Below the battery tray, rubbing on the bracket that secures the Transmission Control Module (TCM).. Chafing here can damage wiring for power, ground, or communication to the TCM and solenoids, potentially causing a P0746 code. Damage may be internal to the harness loom and not visible externally.
• Transmission Harness Chafe Point 2 — On the studs for the transmission oil pan / control valve body cover.. Vibration can cause the harness to rub through on the sharp edges of the cover studs, shorting or opening circuits related to the pressure control solenoid.
• Transmission Harness Chafe Point 3 — At the bracket securing the transmission oil cooler line.. Contact with this bracket can cause similar harness damage, interrupting signals to and from the transmission assembly.

Real Owner Repair Stories

• Reddit user in r/Cadillac (2024 Cadillac XT6, failure at ~30 days old.) — Sudden loss of acceleration while pulling into traffic; transmission completely failed.
  ❌ Tried (didn't work) N/A - vehicle was towed directly to dealer.
  ✅ What actually fixed it Vehicle was awaiting a transmission replacement. The dealer confirmed it was one of 'dozens' of vehicles on their lot with the same issue, and parts were on backorder. This story strongly supports the TSB regarding a widespread manufacturing defect in 2024 models.

"I Checked Everything" — The Actual Cause

• A common diagnostic trap for this code is not a failed smoke test, but a failed valve body replacement. Technicians may follow the code's definition and replace the pressure control solenoid or the entire valve body assembly. However, GM TSBs PIP5974E and PIP5974A explicitly warn that these parts are not the cause. The code returns because the root cause—an internal mechanical failure of the 1-2-3-4-5-6 clutch snap ring—was not addressed, leading to a costly and ineffective repair.

OEM Part Supersession History

• N/A → Required Repair Kit — Per TSB PIP5974E, a single part is not sufficient. The snap ring failure requires a mandatory replacement of the entire clutch piston housing and related components as a set to ensure the repair holds.
  Heads up: Replacing only the snap ring without also replacing the '(590) 1-Reverse and 1-2-3-4-5-6 Clutch Piston Housing' and other listed components will lead to a repeat failure. The full list includes: Piston Housing (590), Inner Seal (591), Piston (592), Return Spring (593), Spring Retaining Ring (594), Wave Plate (595), Clutch Plate (596), Friction Plate (597), Backing Plate (598), Backing Plate Retaining Ring (599), and Piston Seal (600).

Model Year Variations Within This Range

• 2024 (primarily): Transmissions manufactured between Julian dates 23 274 and 24 113 (October 1, 2023 - April 22, 2024) are identified by GM as having a high likelihood of an out-of-round 1-2-3-4-5-6 clutch snap ring, which is the primary cause of P0746 on these vehicles.
• 2023: Some 2023 models were subject to recalls (NHTSA #23V172000) for transmissions built with an incorrect sun gear, which could lead to a loss of drive power. While this is a different failure mode, it points to a pattern of transmission manufacturing defects during this production period.