P0742 on Cadillac: How to Diagnose & Fix
Torque Converter Clutch Circuit Stuck On
2 Cadillac models · 2 documented issues · $200-$3,500 repair
P0742 on Cadillac by model: symptoms, diagnosis and fix
The Cadillac XT5 uses an 8-speed (2017-2019) or 9-speed (2020+) automatic transmission. The 8-speed shares the torque converter shudder issue with other GM 8-speed vehicles. The 9-speed (GM 9T50/9T65) can have harsh shifts, delayed engagement, and shift hunting. Both transmissions have been subject to multiple software calibration updates from GM. The 9-speed is particularly sensitive to fluid condition and requires proper Dexron HP fluid.
Common Symptoms
- Shudder at light throttle between 25-50 mph (8-speed)
- Harsh or clunky 1-2 shift
- Delayed engagement from Park to Drive
- Transmission hunting between gears on hills (9-speed)
- Hesitation on acceleration from stop
How to Fix
First step is a TCM software update at the dealer - multiple calibrations have been released. For 8-speed shudder, a fluid exchange with Mobil 1 LV ATF HP may resolve it. The 9-speed typically responds well to software updates. Persistent issues may require torque converter replacement (8-speed) or valve body replacement (9-speed).
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- AW-1 Automatic Transmission Fluid (8-speed models, 1 qt)OEM19256039Cross-refACDelco 10-4062 (same fluid, retail number), GM 19256040 (Canada), Idemitsu Type AW-1 / TLS-LV ATF$11–$22
For 2017-2019 XT5, which uses the Aisin AWF8F45 (AF50-8) 8-speed transaxle - NOT the GM 8L45 named in the issue write-up (8L45 is a rear-drive unit and does not fit the transverse XT5). Correction that matters for buyers: Mobil 1 LV ATF …
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Sources for this issue (1)
The CT5 uses GM's 10-speed automatic (10L80) that can exhibit harsh shifts, delayed engagement, and shift hunting, particularly when the adaptive learning resets. The 10-speed has very complex shift logic and can take 500+ miles to fully adapt to a driver's pattern after a battery disconnect, TCM update, or reset. Some CT5 owners report persistent shift quality issues even after adaptation. The CT5-V and CT5-V Blackwing have refined calibrations but can still exhibit occasional harsh shifts.
Common Symptoms
- Harsh 1-2 or 3-4 shifts
- Delayed shift from Park to Drive/Reverse
- Transmission hunting between gears on hills
- Shift quality changes after battery disconnect or service
- Clunky low-speed maneuvers
How to Fix
Have dealer perform latest TCM software calibration - GM releases regular updates. Allow 500+ miles after any reset for the transmission to relearn. For persistent issues, a full transmission fluid exchange with Mobil 1 LV ATF HP can improve shift quality. Very few CT5s require hardware repair.
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 Cadillac?
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 Cadillac it is documented across 2 models: XT5, CT5.
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 Cadillac?
Published repair estimates on Cadillac range from $200 to $3,500 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.