P0742 on GMC: How to Diagnose & Fix
Torque Converter Clutch Circuit Stuck On
6 GMC models · 7 documented issues · 5 critical · $150-$4,500 repair
P0742 on GMC by model: symptoms, diagnosis and fix
The 8L90 8-speed and 10L80/10L90 10-speed automatic transmissions experience shuddering during light throttle acceleration, particularly at highway speeds between 35-60 mph. The issue is caused by the torque converter lock-up clutch slipping and chattering. Harsh shifts between gears, especially 1st to 2nd and 2nd to 1st, are also commonly reported.
Common Symptoms
- Vibration or shudder during light acceleration at 35-60 mph
- Harsh or jerky shifts between gears
- Transmission slipping sensation
- Shudder when torque converter locks up
- Intermittent transmission hesitation
How to Fix
Transmission fluid flush with updated Mobil 1 Synthetic LV ATF HP fluid (GM part number 19417577). Torque converter replacement. Transmission control module software update. Complete transmission replacement in severe cases.
Sources for this issue (1)
P0700 itself is only a flag: the Transmission Control Module has stored one or more transmission faults and is requesting the MIL. On Sierra 1500s with the 6L80 (and 6L90 on heavier variants) 6-speed automatic, the notable design issue is that the TCM is integrated into the valve body as a TEHCM (transmission electro-hydraulic control module), bolted inside the pan and sitting in 180-250°F fluid. Repeated heat cycling degrades the module and its integrated pressure switches and solenoids. When the TEHCM or a shift/pressure-control solenoid begins to fail, it sets specific sub-codes (e.g., P2534, P0742, P0761) plus the umbrella P0700, and the truck can exhibit harsh or missed shifts, slipping, or limp mode. Critically, on the 6L80/6L90 the solenoids are over-molded into the non-serviceable TEHCM and generally can't be replaced individually.
Common Symptoms
- Check engine light with transmission sub-codes
- Harsh or delayed shifts
- Slipping
- Loss of gears / limp mode
- Torque converter shudder
How to Fix
P0700 alone is not actionable — pull the transmission-specific sub-codes with a capable scanner to find the real fault. Check fluid level/condition first. Repairs commonly involve replacing the TEHCM/valve body assembly (solenoids are integrated and non-serviceable) and re-learning shift adaptives; the new TEHCM must be programmed to the VIN. Address any fluid overheating cause to prevent recurrence.
Sources for this issue (1)
The Allison 1000 (gas) and Allison 2000 (diesel) 6-speed automatic transmissions used in Sierra 2500HD/3500HD are widely regarded as extremely durable, but the Transmission Control Module (TCM) and solenoid pack do develop faults. Common issues include harsh 1-2 shifts, transmission sticking in one gear, slip codes, and the truck going into limp mode (3rd gear only). The Allison's proprietary Transynd fluid is critical — using non-approved fluid is the leading cause of premature solenoid wear. TCM software updates from GM address most calibration-related shift complaints.
Common Symptoms
- Harsh or clunky 1-2 upshift
- Transmission stuck in 3rd gear (limp mode)
- Delayed engagement from Park to Drive
- Slip or flare during 2-3 shift
- Check engine light with transmission codes (P0700, P0730, P0751)
- Transmission not shifting above 3rd gear under load
How to Fix
TCM software update at dealer. Allison Transynd fluid service (drain/fill every 30k miles, full exchange every 60k). Solenoid pack replacement (Allison 29539579). TCM replacement if software update fails. Always use genuine Allison Transynd TES-295 or Mobil Delvac 1 ATF — not GM DEXRON products.
Sources for this issue (1)
The Allison 1000 and 2000 series automatic transmissions paired with Duramax engines in the Sierra 3500HD exhibit torque converter clutch shudder during light throttle cruising between 40–65 MPH as the TCC applies and releases. This is caused by degraded transmission fluid, worn TCC friction material, or contamination in the hydraulic circuit. GM and Allison have acknowledged this issue through multiple fluid specification updates and TSB 07-07-30-022.
Common Symptoms
- Vibration or shudder between 40–65 MPH at light throttle
- Shudder disappears under hard acceleration or deceleration
- Transmission hesitation or clunk when TCC engages
- Rough or inconsistent lockup feel during highway cruising
- Transmission fluid with burnt smell or dark discoloration
How to Fix
Drain and refill with Allison-approved TES-295 or TES-468 fluid (Transynd or equivalent); do not use generic ATF. If shudder persists after fluid service, a complete torque converter replacement (remanufactured unit $400–$800) and valve body cleaning is required. GM TSB 07-07-30-022 outlines the fluid change procedure and updated fill volume specifications. Complete transmission fluid flush recommended every 50,000 miles for prevention.
Sources for this issue (1)
The heavy-duty 4L80E (4L85E behind the 8.1L and the diesel) fitted to Savana 2500 and 3500 vans develops a distinct failure set from the 1500's 4L60E. Owners report shuddering around 45 mph as the torque converter clutch tries to lock, hard or late shifts, no downshift on throttle demand, and in advanced cases the van reaching operating temperature and then behaving as though it is in neutral in every gear. Root causes documented on 3500 vans include a failed TCC PWM solenoid or its electrical circuit, worn valve body bores, and pressure loss from a worn pump. Commercial-fleet duty cycles - constant loaded stop-and-go, cutaway upfit weight at the top of the GVWR - accelerate all of it.
Common Symptoms
- Shudder at approximately 45 mph
- Harsh or late upshifts
- No downshift when throttle is applied
- Neutral-like condition in all gears when hot
- Overdrive inoperative
- Check engine light with transmission codes
How to Fix
No recall. GM bulletin 08-07-30-001 covers 4L80E harsh/delayed shifts, slipping and no forward/reverse. Diagnose electrically first: a TCC PWM solenoid or its wiring is a comparatively cheap repair ($350-$700) and P1860 points straight at it. If pressure tests show pump or valve body wear, or the van has lost gears, the fix is a rebuild or reman unit at roughly $2,500-$4,500 installed for a 3500. On any van used as a work truck, fit an auxiliary cooler and service the fluid every 50,000 miles rather than following the severe-service book interval.
Sources for this issue (3)
The 8-speed (8L90) and 10-speed (10L80) automatic transmissions in the Yukon XL develop a torque converter clutch (TCC) shudder felt as a vibration or shake at light throttle between 25-50 mph. The shudder mimics driving over rumble strips. GM issued multiple TSBs (18-NA-355, 19-NA-193) and eventually reformulated the transmission fluid specification. The root cause is the TCC friction material interaction with the original Dexron HP fluid formulation.
Common Symptoms
- Vibration or shudder at 25-50 mph under light throttle
- Feels like driving over rumble strips
- Shudder disappears under heavy acceleration
- Vibration most noticeable in overdrive gears
- Intermittent — may come and go
How to Fix
First-line fix: complete transmission fluid flush and fill with GM-approved Mobil 1 Synthetic LV ATF HP (Blue Label) — NOT the original red-label Dexron HP. This updated fluid resolves the shudder in approximately 80% of cases. If shudder returns within 30,000 miles of the fluid change, the torque converter requires replacement. Do NOT use aftermarket friction modifiers or additives — they void the GM powertrain warranty and can damage the transmission.
Sources for this issue (1)
P0742 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0742 mean on a GMC?
P0742 stands for "Torque Converter Clutch Circuit Stuck On." P0742 means the torque converter clutch (TCC) circuit is stuck on, meaning the lockup clutch that mechanically links the engine to the transmission stays engaged when it should release. The computer commands the clutch on and off, and when it detects the converter clutch remaining applied, it sets this code. The classic symptom is the engine stalling when coming to a stop, similar to driving a manual without pushing the clutch in, along with possible harsh shifts or poor fuel economy. It points to a hydraulic or solenoid problem inside the transmission rather than the engine. On GMC it is documented across 6 models: Sierra 1500, Sierra 2500HD, Sierra 3500HD, Savana, Yukon XL, C/K 1500.
What are the most common causes of P0742?
The most common causes of P0742 are: Stuck or failed torque converter clutch solenoid, Stuck valve in the valve body (TCC apply valve), Contaminated or degraded transmission fluid, Internal transmission hydraulic leak holding the clutch on, Wiring or connector fault to the TCC solenoid, Faulty torque converter, Dirty or clogged transmission filter. The specific cause varies by vehicle.
How much does it cost to fix P0742 on a GMC?
Published repair estimates on GMC range from $150 to $4,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0742 on a different make?
View P0742 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.