P0746 on 2019-2024 Cadillac XT4: Causes, Symptoms, and Fixes

What's Unique About the 2019-2024 Cadillac XT4

The Cadillac XT4, equipped with a 9T-series (specifically 9T50) automatic transmission, has a known issue documented in General Motors Technical Service Bulletins (TSBs). Specifically, TSB #PIP5974E states that out-of-round snap rings for the 1-2-3-4-5-6 clutch can cause code P0746. This means the problem is often a mechanical failure inside the transmission, rather than a simple faulty solenoid. TSB PIP5974A explicitly warns technicians *not* to replace the valve body or solenoid body for this concern, as it is not related to the root cause. This makes accurate diagnosis crucial to avoid unnecessary and ineffective repairs.

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 in Drive, Neutral, or Reverse
🎬 See how to diagnose common 9T50 issues when the vehicle won't move.
• Slipping sensation when trying to accelerate from a stop
• Check Engine Light is on
• Harsh or delayed gear shifts
• Transmission slipping
• Vehicle stuck in one gear (limp mode)
• Increased fuel consumption

Most Likely Causes

1. Internal Transmission Snap Ring Failure 🔴 High Probability → Shop Transmission Assembly This is a well-documented issue for the 9T-series transmission in this vehicle, as cited in GM TSB #PIP5974E and PIP5974A. These bulletins state that the 1-2-3-4-5-6 clutch backing plate retaining ring or spring retaining ring can be 'out of round', causing a loss of clutch pressure and setting P0746 or P0747. TSB PIP5974A identifies a specific batch of transmissions built between 10/1/2023 and 4/22/2024 (Julian dates 23274 to 24113) as being highly susceptible.
   How to confirm: Diagnosis requires a transmission specialist. It involves ruling out other causes, then dropping the transmission pan to inspect for excessive metallic debris. TSB 24-NA-088 (for the related P0747 code) suggests that dark, burnt fluid with debris points towards a major internal failure like the snap ring. Ultimate confirmation requires transmission removal and disassembly to inspect the 1-2-3-4-5-6 clutch pack and snap rings.
   Typical fix: The transmission must be removed and disassembled to replace the faulty snap rings and any collateral damage to the clutch pack, piston housing, and seals. TSB PIP5974A lists a full set of 10 related parts within the clutch assembly that need to be replaced. In many cases, a complete transmission rebuild or replacement with an updated unit is the most practical solution. 🎬 Watch: A detailed rebuild walkthrough for this family of GM transmissions.
   Est. part cost: $50-$200 for a rebuild kit containing the rings, but a full transmission replacement can be thousands.
2. Failed Pressure Control Solenoid or Valve Body ⚪ Low Probability → Shop Transmission Clutch Pressure Control Solenoid While solenoids can fail, GM has explicitly stated in TSB PIP5974A not to replace the solenoid or valve body for this issue, as it is not the root cause. This cause is only probable if the primary snap ring issue has been definitively ruled out, for example, on a vehicle outside the affected TSB date ranges and with no metal debris in the pan.
   How to confirm: A technician can use a professional scan tool to command the solenoid on and off while monitoring transmission pressure data. The solenoid's electrical circuit can also be tested for resistance and continuity. However, these tests may not be conclusive if the underlying problem is mechanical.
   Typical fix: Replacement of the specific solenoid or the entire valve body assembly. This is performed by removing the transmission oil pan. This should only be done after confirming it is not the more common snap ring failure.
   Est. part cost: $290-$600 for a valve body/solenoid assembly.
3. Low or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly
   How to confirm: Check the transmission fluid level and condition according to the manufacturer's procedure, which must be done at a specific temperature (85–95°C / 185–203°F). The XT4 does not have a traditional dipstick. Dark, burnt, or metallic fluid is a strong indicator of the internal snap ring failure, making this a symptom rather than a root cause.
   Typical fix: If the fluid is low, the leak must be found and repaired. If the fluid is contaminated, a fluid and filter change is insufficient; the source of the contamination (likely the failing clutch pack) must be addressed.
   Est. part cost: $100-$250 for fluid and filter, but this will not solve the underlying mechanical problem.

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly A TCM failure is rare but can cause false codes. It should only be considered after all other mechanical and electrical possibilities have been exhausted. TSB PIP5697E describes a rare scenario where a BCM or wiring issue can cause a false P0747 (related code) at engine shutdown, which could be relevant.
• Wiring Issues: Damage to the wiring harness leading to or inside the transmission can cause an open or short in the solenoid's circuit, mimicking a failed solenoid. The internal transmission wiring harness (GM Part No. 24046896) is a known failure point in some cases.

Diagnosis Steps

1. Verify the transmission fluid level and condition. This must be done at the correct operating temperature of 85–95°C (185–203°F). Note the fluid color and smell; dark, burnt fluid with a metallic sheen points to internal failure.
2. Use a professional-grade scan tool to read all codes from the TCM and check for related codes like P0747 or P0700.
3. Check the transmission build date. If it falls between October 2023 and April 2024, the snap ring failure described in TSB PIP5974A is highly probable.
4. Monitor live transmission data with the scan tool. Observe the commanded state versus the actual state of Pressure Control Solenoid 'A' and line pressure readings.
5. Inspect the transmission wiring harness and connectors for any visible damage, corrosion, or loose connections.
6. If electrical checks and fluid level are good, the diagnosis will proceed to internal inspection. This involves dropping the transmission oil pan to check for excessive metal debris, which would confirm a mechanical failure.
7. Based on the strong evidence from TSBs, if debris is found or the vehicle is within the suspect build date range, the next step is transmission removal and disassembly to inspect the 1-2-3-4-5-6 clutch snap rings and related components.

Parts You'll Likely Need

• Transmission Assembly — Due to the high probability of internal mechanical damage (snap rings, clutch pack), a complete remanufactured transmission replacement is often the most effective and warrantied repair. A GM replacement often comes with a 3-year/100,000-mile warranty.
  Trusted brands: GM Genuine Parts, ACDelco
  OEM price range: $4000-$6000+
  Aftermarket price range: $3000-$5000
• Transmission Snap Ring Kit (OEM #24277834) — This is the specific part type identified in TSB #PIP5974E as a primary cause. However, replacing it requires a full transmission teardown and usually involves replacing the entire clutch pack assembly as detailed in TSB PIP5974A.
  Trusted brands: GM Genuine Parts
  OEM price range: $50-$150
  Aftermarket price range: $30-$100
• Transmission Valve Body Assembly — This part should NOT be replaced for this code unless the snap ring failure has been completely ruled out and diagnosis points specifically to a hydraulic control fault. GM TSBs advise against replacing it for this issue.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $400-$700
  Aftermarket price range: $290-$600

Related Codes That Often Appear With This One

• P0747 — This code is for 'Pressure Control Solenoid 'A' Stuck On.' The TSBs (PIP5974E, PIE0720A, PIE0720) list P0746 and P0747 together, as the underlying mechanical snap ring failure can cause either pressure control fault by preventing correct clutch pressure.
• P0700 — This is a generic code that means the Transmission Control Module (TCM) has stored a fault. It's a 'gateway' code that tells technicians to look for more specific transmission codes like P0746.

Technical Service Bulletins (TSBs) & Recalls

• PIP5974E: Communicates that possible transmission 1-2-3-4-5-6 snap rings being out of round can cause code P0746 or P0747.
• PIP5974A: Provides specific transmission build dates (10/1/2023 - 4/22/2024) affected by out-of-round snap rings and lists the full set of clutch components to be replaced during the repair.
• PIE0720A: Closes an engineering investigation into vehicles that will not move, with DTCs P0746 and P0747 set, often due to a broken 1-2-3-4-5-6 clutch piston return spring.
• PIE0720: Initiates an engineering investigation into vehicles that will not move with DTCs P0746 and P0747.

Platform-Specific Known Issues

• A primary issue documented in TSB #PIP5974E is that the 1-2-3-4-5-6 clutch snap rings can be 'out of round,' leading directly to codes P0746 or P0747.
• TSB #PIP5974A further specifies that transmissions built between 10/1/2023 and 4/22/2024 are particularly at risk for this snap ring failure and explicitly warns technicians not to replace the valve body.
• TSBs #PIE0720A and #PIE0720 were issued for engineering investigation into a 'Vehicle Will Not Move' condition associated with codes P0746 and P0747, highlighting the severity of the potential failure.
• Another related issue, per recall N202321843, involves an improperly seated clutch spring retaining ring that can cause P0747 at low mileage, which is mechanically similar to the P0746 issue.

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 hydraulic fault, which could be related to the pump, valve body, or the internal leak caused by 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 lead to an inaccurate reading, which can mask or mimic fluid-related problems.

Scan Tool Commands That Help

• GDS2 (GM Techline Connect): Reset Transmission Pressure Adapts — This service function is used after a repair or to correct incorrect learned pressure values that may be causing shudder or harsh shifting complaints, which can sometimes accompany pressure-related DTCs.
• GDS2 (GM Techline Connect): Active Test - Shift Transmission — Allows a technician to command specific gear shifts while driving to compare the commanded gear versus the actual gear engaged. This helps verify if the clutch circuit associated with P0746 is failing to apply as instructed by the TCM.
• GDS2 (GM Techline Connect): Monitor Transmission Input Speed Sensor (ISS) — When performing 'garage shifts' (P-R-N-D), monitoring the ISS RPM can confirm gear engagement. A delay in the ISS dropping to 0 RPM can indicate a hydraulic apply issue, which is the root of code P0746.

Wiring & Ground Locations

• Transmission Case Connector - Pin B1 — The main electrical connector on the transmission case.. This pin is for the '1-2-3-4-5-6 Clutch' solenoid, which is Solenoid 'A' in the P0746 code context. The wire is Blue and corresponds to circuit 6401. Testing for voltage and continuity at this specific pin is crucial for diagnosing electrical faults in the solenoid circuit.

Real Owner Repair Stories

• Gears Magazine, 'Listen for the Snap' (GM vehicle with a 9T-series transmission (applicable to the XT4)) — Slipping condition in forward gears, vehicle would barely move unless high throttle was applied. DTC P0746 was set.
  ❌ Tried (didn't work) The article notes that fluid level and pressure were good, and warns against assuming it's just a solenoid or valve body issue.
  ✅ What actually fixed it The root cause was the known GM issue of an out-of-round or improperly seated snap ring for the 1-2-3-4-5-6 clutch. The fix required transmission disassembly to inspect and replace the snap ring and any related clutch components. The article notes a loud 'popping' noise should be heard when the new snap ring is installed correctly.

"I Checked Everything" — The Actual Cause

• While not a smoke test issue, P0746 on the 9T50 transmission follows a similar pattern where standard electrical tests can be misleading. A technician might test the Pressure Control Solenoid 'A' circuit and find that it has proper resistance and is not open or shorted. However, the code persists because the actual failure is not electrical but mechanical: an out-of-round snap ring deep inside the transmission is preventing the clutch pack from receiving hydraulic pressure. The TCM sets the P0746 'performance' code because it commands the solenoid and sees via gear ratio calculations that the clutch does not apply, even though the solenoid's electrical circuit appears intact.

OEM Part Supersession History

• 24298758, 24294895, 24045610 → 24046896 — Updated internal transmission wiring harness assembly.
  Heads up: The newest part number, 24046896, should be used for service to ensure the latest revisions are incorporated. Using old stock is not recommended.

Model Year Variations Within This Range

• 2019-2024: The 9T50 transmission can be equipped with different versions of the Electronic Transmission Range Select (ETRS) system, known as GEN 1 or GEN 2. This determines which control module is responsible for shifter functions and where related diagnostic trouble codes are stored. While not a direct cause of P0746, it is a key difference a technician must be aware of when diagnosing the overall transmission control system.