P0742 on 2001-2008 Chevrolet Silverado 2500: TCC Stuck On Causes and Fixes

What's Unique About the 2001-2008 Chevrolet SILVERADO 2500

The 2001-2008 Silverado 2500 spans two generations (GMT800 and GMT900) and used different transmissions, primarily the 4L80-E/4L85-E and the Allison 1000. On models equipped with the 4L80-E, a very common cause for P0742 is not just the TCC solenoid itself, but a worn TCC regulator valve bore in the transmission's valve body. This wear allows hydraulic pressure to leak, causing the clutch to apply unintentionally. 🎬 Watch: Understanding how the P0742 circuit works and fails. Many owners find that simply replacing the solenoid doesn't fix the problem without also addressing the worn valve body.

Diagnostic Flowchart

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

Generation note: This range covers the first generation GMT800 (2001-2006, and 2007 'Classic') and the second generation GMT900 (2007-2008). The GMT800s commonly used the 4L80-E transmission, which is well-known for valve body wear issues related to this code. GMT900 models may have a 6L90 or Allison 1000 transmission, which can have different failure points, though the TCC solenoid remains a common cause.

Symptoms You May Notice

• Engine stalls or dies when coming to a stop.
• A feeling like the vehicle is trying to lurch forward against the brakes at a stop.
• Engine surges while in gear at a stop. [⭐ MANUFACTURER TSB — highest authority] Bulletin #PIP4290A
• Harsh or delayed shifts.
• Transmission overheating.
• Reduced fuel economy.
• Check Engine Light is on.

Most Likely Causes

1. Faulty Torque Converter Clutch (TCC) Solenoid 🔴 High Probability → Shop Automatic Transmission Torque Converter The solenoid is an electronic part submerged in hot transmission fluid, leading to eventual failure. Debris in the fluid can also cause it to stick internally or short out electrically.
   How to confirm: Use a scan tool to command the TCC solenoid on and off. After removal, the solenoid can be tested with a multimeter. For the PWM-style solenoid in these 4L80-E transmissions, a healthy resistance reading is typically between 10 and 15 ohms. A reading far outside this range indicates a failed solenoid.
   Typical fix: Replace the TCC solenoid, along with the transmission filter and fluid. The correct OEM part is ACDelco 24227792.
   Est. part cost: $40-$100
2. Worn TCC Regulator Valve Bore in Valve Body 🔴 High Probability → Shop Transmission Valve Body Especially common in the 4L80-E transmission, the steel valve constantly oscillates within the softer aluminum valve body, causing the bore to wear over time. This wear allows hydraulic fluid to leak and improperly engage the TCC.
   How to confirm: This is difficult to confirm without removing the valve body for inspection, often with a vacuum test kit. If a new TCC solenoid does not fix the issue, a worn valve bore is the next logical cause.
   Typical fix: Install an oversized TCC regulator valve kit, which requires reaming the valve body bore. Sonnax makes a well-regarded kit (Part #34994-01K) specifically for this repair. Alternatively, replace the entire valve body with a remanufactured unit.
   Est. part cost: $70-$350
3. Dirty or Low Transmission Fluid 🟡 Medium Probability → Shop Transmission Assembly Over time, fluid breaks down and clutch material contaminates it, which can clog the small passages in the valve body and cause solenoids to stick.
   How to confirm: Check the transmission fluid level and condition. If it's dark, burnt-smelling, or contains metallic debris, it needs to be changed and is a sign of internal problems.
   Typical fix: Perform a transmission fluid and filter change. In severe cases where debris is found in the pan, a more thorough diagnosis is needed as this points to larger internal damage.
   Est. part cost: $50-$150
4. Wiring Harness Issues (Internal or External) ⚪ Low Probability The external harness can be damaged by heat or chafing. The internal transmission harness, constantly bathed in hot fluid, can become brittle, causing wires to crack and short to power, keeping the TCC solenoid energized.
   How to confirm: Visually inspect the external wiring harness. Disconnecting the main 20-way connector at the transmission is a key test; if the stalling stops, the issue is internal to the transmission (solenoid, internal harness, valve body). If it continues, the short is in the external vehicle harness. [⭐ MANUFACTURER TSB — highest authority] Bulletin #PIP4290A
   Typical fix: Repair or replace the damaged section of the wiring harness. If the internal harness is faulty, it must be replaced, which requires dropping the pan and valve body.
   Est. part cost: $20-$200

Rare But Worth Checking

• Torque Converter Failure: → Shop Automatic Transmission Torque Converter The internal clutch of the torque converter itself can fail mechanically, causing it to stay locked. This is less common than a solenoid or valve body issue and usually produces more noise or shuddering.
• Faulty Powertrain or Transmission Control Module (PCM/TCM): → Shop Transmission Assembly In rare cases, the module's internal driver circuit can fail, sending a constant 'on' signal to the TCC solenoid. TSB PIP4290A suggests swapping the TCM with a known good unit as a final diagnostic step after ruling out wiring and internal transmission faults.

Diagnosis Steps

1. Check the transmission fluid level and condition. Note any burnt smell or debris, which indicates a more serious internal failure.
2. Use a high-quality OBD-II scanner to confirm code P0742 and check for any other pending or active codes.
3. With the scanner, monitor the TCC slip RPM and solenoid command status while driving. Confirm if the computer is commanding the TCC on at inappropriate times or if slip RPM is zero at a stop.
4. Perform the key diagnostic step from TSB PIP4290A: Disconnect the 20-way transmission connector. Start the engine and shift into gear. If the stalling at a stop is eliminated, the fault is internal to the transmission. If the stalling continues, the issue is an external electrical short keeping the circuit energized.
5. If the issue is internal, drop the transmission pan and inspect for excessive metal debris.
6. Visually inspect the internal wiring harness for brittle or damaged wires.
7. Test the resistance of the TCC solenoid with a multimeter. It should read between 10-15 Ohms. A significantly different reading confirms a bad solenoid.
8. If the solenoid and wiring test good, the next most likely cause is a worn valve body. This requires removal and inspection, preferably with a vacuum testing tool, to check for wear in the TCC regulator valve bore.

Parts You'll Likely Need

• Torque Converter Clutch (TCC) PWM Solenoid (OEM #ACDelco 24227792) — This is the most common component to fail electrically or become stuck due to debris, directly causing the P0742 code.
  Trusted brands: ACDelco (GM Genuine), Rostra
  OEM price range: $60-$120
  Aftermarket price range: $40-$80
• Transmission Valve Body Repair Kit (TCC Regulator) (OEM #Sonnax 34994-01K) — Specifically for the common 4L80-E, the TCC regulator valve bore wears out. This kit provides an oversized valve to restore hydraulic integrity, often fixing the root cause when a new solenoid doesn't.
  Trusted brands: Sonnax
  OEM price range: N/A
  Aftermarket price range: $70-$150
• Transmission Filter and Gasket Kit — This must be replaced anytime the transmission pan is removed for service.
  Trusted brands: ACDelco, Wix, ATP
  OEM price range: $40-$70
  Aftermarket price range: $20-$40

Technical Service Bulletins (TSBs) & Recalls

• PIP4290A: Addresses a surge or stall when in gear at a stop, associated with DTC P0742, and provides diagnostic guidance for Allison-equipped trucks.
• PIP4290C: A later revision that supersedes PIP4290A and updates the applicable model years, confirming the diagnostic procedure remains relevant.

Platform-Specific Known Issues

• GM Technical Service Bulletin PIP4290A (and later versions like PIP4290C) specifically addresses a surge or stall at a stop with DTC P0742. It provides a key diagnostic step: disconnecting the 20-way transmission connector to isolate the fault as internal or external to the transmission. This TSB applies to models with the Allison 1000 transmission as well.
• On 4L80-E equipped models, wear in the TCC regulator valve bore within the valve body is a well-documented failure pattern that leads to P0742. Many experienced technicians and forum users recommend inspecting this or installing the Sonnax repair kit preventatively during a solenoid replacement.

Mechanic-Grade Diagnostic Values

• 4L80-E TCC PWM Solenoid Resistance — expected: 10-15 Ohms (for late model '94+). Failure: A reading significantly outside this range, or open/shorted, indicates a failed solenoid.
• Allison 1000 (2001-2005) TCC Solenoid Resistance — expected: 10.5-11.5 Ohms. Failure: A reading outside this range indicates a faulty solenoid.
• Allison 1000 (2006-2009) TCC Solenoid Resistance — expected: 5.5 Ohms. Failure: A reading outside this range indicates a faulty solenoid.
• 4L80-E Valve Body TCC Regulator Bore Vacuum Test — expected: 16 in-Hg or higher. Failure: A vacuum reading below 16 in-Hg indicates significant wear and pressure loss, requiring a valve body repair kit.

Scan Tool Commands That Help

• Tech II (or equivalent professional scanner): Monitor Turbine Speed Sensor — For Allison transmissions, when diagnosing P0742. While coming to a stop, the turbine speed should quickly drop to zero. If it lags or fails to reach zero, it confirms the torque converter clutch is dragging or staying partially applied.

Wiring & Ground Locations

• G101 — Located on the lower front of the engine block.. This is a primary ground point for the Engine Control Module (ECM) and Transmission Control Module (TCM). A poor connection here can cause erratic behavior and false codes from either module.
• G103 — Located on the cowl at the left rear of the engine compartment, above the brake booster.. This ground serves the Body Control Module (BCM) and the Data Link Connector (DLC). A fault here can cause communication issues with scan tools and other control modules.
• 4L80-E Transmission Case Connector - Pin S — The main round electrical connector on the passenger side of the 4L80-E transmission.. Pin S is the control circuit for the TCC PWM Solenoid. This is the specific pin to test for voltage or shorts when diagnosing an external wiring fault.
• Allison 1000 Transmission Case Connector - Pin F — The main round electrical connector on the Allison transmission.. Pin F is the control for the TCC solenoid on 2001-2005 models. A wiring issue on this circuit can cause P0742.

Real Owner Repair Stories

• LS1TECH - Camaro and Firebird Forum Discussion (2000 Camaro with a 4L80-E swap (same transmission)) — Code P0742 (converter clutch circuit stuck on) appeared after previous transmission work.
  ❌ Tried (didn't work) The transmission was built with a Jakes stage 2 kit and a Circle D triple-disc converter. The initial problem was TCC applying at strange times.
  ✅ What actually fixed it Installing a completely new, rebuilt valve body resolved the P0742 code. This suggests the original or initially repaired valve body had an internal hydraulic leak or a faulty component (like the TCC regulator valve) that was not fixed by just solenoid replacement.

OEM Part Supersession History

• Unknown early 4L80-E TCC Solenoid PNs → ACDelco 24227792 — GM has updated part designs over the years to integrate new materials and technologies for reliability.
  Heads up: Early ('91-'93) 4L80-E transmissions used a different resistance solenoid (20-40 ohms). Using a modern low-resistance solenoid (10-15 ohms) on an early computer without a PROM update can cause issues. The vehicles in this article's range (2001-2008) all use the later, low-resistance PWM solenoid.

Model Year Variations Within This Range

• 2001-2005 (Allison 1000): These 5-speed Allison transmissions use a TCC solenoid with a resistance of 10.5-11.5 Ohms.
• 2006-2009 (Allison 1000): These 6-speed Allison transmissions introduced a different TCC solenoid design with a much lower resistance of approximately 5.5 Ohms. The solenoids are not interchangeable between the 5-speed and 6-speed models.
• 2004 (Allison 1000): In 2004, a "G" solenoid was added to the valve body to reduce line pressure at a standstill to prevent pump noise. While not directly the TCC solenoid, it represents a change in the hydraulic system within this vehicle range.