P0747 on 2017-2022 GMC Canyon 8L45: Pressure Control Solenoid 'A' Stuck On Causes and Fixes

What's Unique About the 2017-2022 GMC Canyon

The 8L45 and related 8L90 transmissions in this generation of GM trucks are known for several issues, including torque converter shudder and harsh shifting. Code P0747 is specifically linked to a known wear problem within the transmission control valve body. The aluminum bore for a feed limit valve wears over time, causing a pressure leak that prevents the solenoid from operating correctly. This issue is so common that GM has issued multiple Technical Service Bulletins (TSBs) and a Special Coverage program to address it, often by replacing the entire valve body.

Symptoms You May Notice

• Check Engine Light is on
• Transmission gets stuck in one gear (often 5th gear, known as 'limp mode')
• Harsh, jerky, or delayed shifts, especially the 1-2 shift
• Transmission may not shift at all
• Slipping while accelerating
• Reduced fuel economy
• Delayed engagement when shifting from Park to Drive

Most Likely Causes

1. Worn Transmission Control Valve Body 🔴 High Probability → Shop Transmission Valve Body The valve bores within the original aluminum valve body are prone to wear, specifically at the feed limit valve. This wear creates a hydraulic pressure leak, preventing the solenoid from functioning as commanded and triggering P0747. This is a well-documented design flaw acknowledged by GM through TSBs and a special coverage program.
   How to confirm: A professional technician will scan for the code and inspect the transmission fluid by dropping the pan. Per TSB 24-NA-088, clean, red fluid (even if darkened from normal use) with minimal metallic debris on the magnet points directly to a valve body issue. Conversely, fluid that is dark, has a burnt odor, and contains significant clutch material indicates a more severe internal failure requiring a transmission rebuild or replacement.
   Typical fix: Replace the entire transmission control valve body assembly with an updated part. After installation, a solenoid valve characterization reprogramming procedure is required. 🎬 Watch: Complete GM 8-speed valve body overhaul guide For some newer models, GM has issued TSB 25-NA-255 which details an internal repair of the valve body using an updated steel feed limit valve and a stronger spring, which is a more targeted and less expensive fix. 🎬 Watch: How GM's new steel valve fixes the P0747 issue
   Est. part cost: $500-$1400 for a full assembly, $50-$150 for the internal repair kit.
2. Low or Contaminated Transmission Fluid 🟡 Medium Probability → Shop Transmission Assembly The 8L45 transmission is sensitive to fluid condition. The original factory fluid was susceptible to moisture absorption, which could lead to shudder and other shifting problems. While low or dirty fluid can cause shifting issues, for P0747 it is more often a symptom or contributing factor rather than the root cause.
   How to confirm: Check the transmission fluid level and condition. The fluid should be at the correct level and appear clean and red. Dark, burnt, or metallic-flecked fluid indicates a problem beyond just the fluid itself.
   Typical fix: Perform a transmission fluid and filter change using the correct specification fluid (Mobil 1 Synthetic LV ATF HP). If the fluid is heavily contaminated, this will not solve the underlying mechanical valve body problem but is a necessary step during its replacement.
   Est. part cost: $100-$200
3. Faulty Pressure Control Solenoid 'A' ⚪ Low Probability → Shop Transmission Valve Body While the code directly names the solenoid, on this platform, the solenoid itself is rarely the root cause. The failure is almost always in the hydraulic circuit within the valve body that the solenoid controls. The solenoid is an electronic component that is overbuilt for its application and rarely fails electrically.
   How to confirm: A technician can test the solenoid's resistance and command it on/off with a high-level scan tool. However, this is often misleading as the solenoid can test perfectly fine while the hydraulic passage in the valve body is worn and leaking pressure.
   Typical fix: Replacing only the solenoid is not a recommended or lasting fix. The entire valve body assembly should be replaced or repaired per the latest TSBs.
   Est. part cost: $50-$150

Rare But Worth Checking

• Transmission Control Module (TCM) Failure: → Shop Transmission Assembly A faulty TCM could theoretically command the solenoid to stay on, but this is far less common than the mechanical failure of the valve body. Usually, a bad TCM will present with multiple, erratic codes or communication errors.
• Wiring Harness Issue: Damage to the internal or external transmission wiring harness could cause a short or open circuit, leading to this code. This is uncommon but possible, especially if the vehicle has been serviced recently or has underbody damage.

Diagnosis Steps

1. Verify the presence of code P0747 using an OBD-II scanner.
2. Check for any accompanying transmission codes, such as P0796 or P0700.
3. Check the vehicle's VIN against GM's Global Warranty Management system to see if it is covered under Special Coverage N242454441.
4. If covered, take the vehicle to a GM dealer for a free repair, which typically involves replacing the valve body.
5. If not covered, proceed with diagnosis. Drop the transmission pan and inspect the fluid and pan magnet per TSB 24-NA-088.
6. If the fluid is relatively clean with minimal debris, the cause is the transmission control valve body.
7. If the fluid is dark, burnt, or full of clutch debris, suspect a more severe internal transmission failure requiring a rebuild or replacement in addition to the valve body.
8. Replace the transmission control valve body or perform the internal repair outlined in TSB 25-NA-255.
9. After replacement, perform the Transmission Control Solenoid Valve Characterization Programming using a compatible scan tool.

Parts You'll Likely Need

• Transmission Control Valve Body Assembly (OEM #24299626 (Verify with VIN)) — This is the primary point of failure for code P0747 on these vehicles, as confirmed by multiple GM Technical Service Bulletins.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $500-$1400
  Aftermarket price range: $400-$900

Related Codes That Often Appear With This One

• P0796 — This code is for Pressure Control Solenoid 'C' Stuck Off. TSB PIP5425A explicitly mentions that P0747 and P0796 may appear together, indicating a widespread hydraulic control issue within the valve body.
• P0700 — This is a generic code indicating the TCM has requested the check engine light. It is a general fault code that is stored alongside more specific transmission codes like P0747.
• P0741 — This code for 'Torque Converter Clutch Circuit Performance or Stuck Off' is often seen on these transmissions and relates to the same family of hydraulic control issues, frequently caused by degraded fluid or valve body wear.

Technical Service Bulletins (TSBs) & Recalls

• 24-NA-088: Provides diagnostic advice for P0747, differentiating between a valve body failure and a more severe internal transmission failure based on fluid condition.
• N242454441: A Special Coverage program from GM that extends the warranty for the transmission control valve to 15 years/150,000 miles for the condition causing P0747.
• PIP5425A: An early TSB from 2016 acknowledging that GM was investigating the cause of P0747 and P0796 codes on new 2017 models with 8-speed transmissions.
• 25-NA-255: A more recent TSB (Sept. 2025) that instructs technicians to repair the valve body internally with an updated steel feed limit valve and spring, rather than replacing the whole assembly.

Platform-Specific Known Issues

• GM has issued Special Coverage program N242454441 which extends the warranty on the transmission control valve body to 15 years or 150,000 miles for this specific issue.
• TSB 24-NA-088 provides diagnostic guidance, noting that in most cases of P0747, only the control valve body needs replacement, provided the transmission fluid is not heavily contaminated with clutch material.
• A newer TSB, 25-NA-255, provides instructions for an internal repair of the valve body with an updated steel feed limit valve and spring, which may be performed instead of a full replacement.
• The 8L45 transmission in these trucks is also the subject of class-action lawsuits regarding harsh shifting and torque converter shudder, indicating widespread issues with this transmission family.

Mechanic-Grade Diagnostic Values

• Resistance of Pressure Control Solenoids S1-S7 — expected: 4.5-5.5 Ohms. Failure: A reading outside this range indicates a faulty solenoid coil.
• Resistance of On/Off Solenoids S8-S9 — expected: 11-13 Ohms. Failure: A reading outside this range indicates a faulty solenoid coil.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Solenoid Valve Characterization Programming (MCVM) — This is mandatory after replacing the transmission control valve body. It uses the new valve body's Part Unique Number (PUN) and the transmission's Unique Number (TUN) to download the correct solenoid performance data from GM's servers to the TCM. Failure to perform this step will result in poor shift quality and potential component damage.
• GDS2 (GM Global Diagnostic System 2): Transmission Service Fast Learn — This procedure is performed in the service bay after the characterization programming. It clears all old adaptive values and quickly relearns the clutch apply pressures. The transmission fluid temperature must be between 167°F (75°C) and 185°F (85°C) for the procedure to run.
• GDS2 (GM Global Diagnostic System 2): Adaptive Learning Drive Cycle — After the Service Fast Learn is complete, a specific drive cycle is required to fine-tune the clutch volume and pressure adapts for smooth shifting under various loads. This involves a series of light-throttle upshifts and coast-down shifts in specific gear ranges.

OEM Part Supersession History

• 24299626 → 24299626 (current) — No direct supersession found for the assembly. However, the service procedure has been updated via TSBs. TSB 25-NA-255 introduced an internal repair kit with an updated steel feed limit valve, changing the repair method from full replacement to in-unit repair for some cases.
  Heads up: The same valve body part number is listed for the entire model range, but programming (Solenoid Valve Characterization) is critical and VIN-specific. An incorrect part or failed programming will cause severe shifting issues.

Model Year Variations Within This Range

• 2017-2019 (Primarily): Vehicles in this range were originally filled with a DEXRON VI fluid that was found to be hygroscopic (absorbs moisture), contributing to torque converter clutch shudder. TSB 18-NA-355 instructs dealers to flush the system and replace the fluid with a new formulation, Mobil 1 Synthetic LV ATF HP, to resolve the shudder issue. While not the direct cause of P0747, fluid condition is critical to the health of the valve body.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Torque Converter Shudder / Harsh Shifting 🔴 High — Very common across all 8L45/8L90 transmissions, especially in 2017-2019 models before a fluid formulation change. (Ref: Multiple TSBs, including 18-NA-355, recommend a specific fluid flush procedure with Mobil 1 Synthetic LV ATF HP.)
• Thermostat Failure 🟠 Medium — A common failure item. Owners on forums report replacement anywhere from 30,000 to 80,000 miles. A key symptom is the engine cooling fan running for an extended time after the engine is shut off.
• Key Stuck in Ignition 🟡 Low — Some owners report the ignition switch failing to recognize the vehicle is in Park, preventing the key from being released.
• Power Steering Failure 🔴 High — Complaints have been filed for intermittent or total loss of power steering assist, sometimes at low mileage.
• Infotainment Screen 'Ghost Touch' 🟠 Medium — Some owners experience the central touchscreen registering phantom inputs, causing random changes to settings, which can be a major distraction.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, a used valve body from a salvage yard is NEVER a smart choice. The root cause of P0747 is a progressive mechanical wear issue due to a design flaw in the original part. A used part will either have the same wear or will develop it shortly, leading to a repeat failure.

What to inspect on the donor part:

• Do not purchase a used, non-remanufactured valve body for this repair.

OEM-only on this vehicle (don't cheap out):

• Transmission Control Valve Body Assembly (TEHCM)

Aftermarket brands forum-validated for this vehicle:

• Sonnax: Offers upgraded internal components like pressure regulator valves and shuttle valve kits that specifically address the wear points in the OEM valve body, providing a more durable repair than the original.
• Valve Body Pro: Offers remanufactured valve bodies that are tested and corrected for common wear issues like actuator feed limit pressure and clutch control pressure.

Brands owners have reported issues with on this vehicle:

• Unknown or unbranded valve bodies from online marketplaces. These are often just cleaned-up used parts with the original flaws still present.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0700 — A general Transmission Control System Malfunction code that often accompanies P0747, indicating the TCM has requested the Check Engine Light to illuminate.
• P0796 — Pressure Control Solenoid 'C' Performance or Stuck Off; this code is frequently seen alongside P0747 as both relate to the same valve body wear issues investigated in TSB PIP5425A.

Frequently Asked Questions