Shudder at 45 mph Under Light Throttle
A 2017 minivan with a 3.6L V6 and 6-speed automatic has 112,000 miles. The owner describes a shudder at 45–50 mph under light throttle, worst when the torque converter clutch engages and after the van is warm. No DTCs are stored. Misfire counters stay at zero, fuel trims are within 3%, and the transmission fluid is dark but not burnt; the level is correct. During a road test, the shudder occurs at 1,500 rpm and 45 mph with TCC slip near 80 rpm when commanded to 0 rpm. Giving more throttle causes a downshift and the shudder disappears. Tires are new and balanced. The fluid service history is unknown.
1. How would you distinguish torque converter clutch shudder from engine misfire using the scan data and a road test?
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The scan data argue against an engine misfire: misfire counters are zero, fuel trims are within 3%, and the symptom appears at light throttle in a narrow speed range. A misfire usually shows up in misfire counters and often worsens with load or shows fuel-trim shifts. The TCC slip data are more specific: 80 rpm of slip when 0 rpm is commanded means the clutch is not holding. The road-test confirmation is to command the TCC off with the scan tool at the same speed and throttle. If the shudder disappears when TCC is commanded off, the torque converter clutch is the source; if it remains, look at ignition, fuel, or engine mounts. Giving more throttle unlocks the converter, which also supports TCC shudder.
2. The fluid is dark. Is a fluid change alone a sound repair? What else must be checked before condemning the converter?
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A fluid change alone is not a sound repair if slip is already measurable. Dark fluid suggests clutch material or heat, and a service may improve apply quality but will not restore a worn converter lining. Before condemning the converter, check for the correct fluid specification, inspect for coolant contamination, verify fluid level at temperature, and check TCC solenoid operation and adaptive learned values. A scan tool should command TCC apply and release while watching slip and line pressure. If the solenoid or valve body is slow or leaking, that can cause shudder without converter failure. I would perform the fluid service and reset TCC adaptives, then re-test; if slip remains excessive, the converter is the likely cause.
3. If the shudder remains after a correct fluid service and TCC-learn reset, what is your next step?
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If the shudder remains after a correct fluid service and TCC-learn reset, I would repeat the commanded TCC-off test to confirm the source, then check TCC apply pressure and solenoid current. A sticking valve body or leaking TCC circuit can mimic a failed converter. If pressure and electrical control are correct but slip persists, the converter clutch is worn and the converter should be replaced. I would also cut open the old converter or inspect the pan for debris; heavy debris means the transmission may have additional damage. I would not replace the entire transmission without pressure and slip testing, because the complaint is isolated to TCC apply under light load.