4L60E · HOT · TCC / LOCKUP
4L60E Hot TCC Dropout / No-Lockup Diagnosis
“Locks cold, drops out hot” is a symptom. The test is to determine whether the PCM stopped commanding lockup or the transmission stopped holding it.
APPLICATION: 1993–2002 F-body 4L60E only where transmission and exact-year controls are positively identified. Do not apply one threshold to all years.
Branch 1 · Command went OFF
- Check brake-switch/TCC-release inputs, throttle/load, coolant/transmission temperature inputs and relevant DTCs.
- On modified cars, inspect the current tune for altered enable/disable schedules before assuming a hardware fault.
Branch 2 · Command stayed ON but slip increased
- Now the failure is downstream of the command: hydraulic apply, converter clutch or internal leakage becomes more likely.
- Reproduce the hot condition while recording commanded state and slip; do not diagnose from a cold driveway test.
After modifications
- Converter stall, camshaft, rear gear, tire diameter and calibration interact.
- A lockup schedule copied from a different combination can create hunting, lugging or repeated apply/release without a failed solenoid.
DO NOT REPLACE YET
Do not replace the converter because lockup disappears hot until you know whether the PCM commanded it off or the clutch slipped while still commanded on.
FPV DIAGNOSTIC RULE
OBSERVE → MEASURE → ISOLATE → PROVE → REPAIR → VERIFY. A code or symptom identifies the next test, not the part to buy.
AFTER THE FAILURE IS PROVEN
Use the proven failed branch—not the original symptom—to choose the replacement. Go from diagnosis to the Parts Verdict →