P0764: Shift Solenoid "C" Intermittent

P0764 is the intermittent-fault member of the shift solenoid C family: the solenoid's electrical circuit momentarily opens, shorts, or glitches and then recovers. The TCM catches the discontinuity — commanded current that briefly doesn't match reality — and flags it. Unlike solenoid C stuck on (P0762) or a hard electrical fault (P0763), this one comes and goes, which usually means shifting that misbehaves unpredictably: occasional harsh or missed shifts, random limp-mode episodes that clear after a restart, then miles of normal driving in between. That intermittent character is what makes it frustrating to catch, because a cold test in the shop often reads perfectly fine. Because the A/B/C labeling varies by transmission, confirm which physical solenoid 'C' is before testing.

The suspects are the usual intermittent-electrical lineup, transmission edition. The case connector where the harness enters the transmission is a notorious spot for spread terminals and fluid-wicked corrosion. Chafed harness sections that only short when the wire flexes, a solenoid winding that opens up once it heats to operating temperature, and fluid contamination inside the case connector all produce a signal that drops out and returns. A marginal ground or supply to the TCM circuit can do the same. Because the fault is temperature- and vibration-sensitive, the diagnosis leans on live-data monitoring, a wiggle test, and noting whether the episodes correlate with heat or rough roads.

For the driver, P0764 shows up as an intermittent check engine light, random harsh or delayed shifts affecting the gears solenoid C controls, and occasional limp-mode episodes that clear on the next restart, separated by normal operation. Symptoms are often worse when the transmission is hot. The car remains driveable, but the erratic engagement quietly stresses the clutches over time, so it's worth chasing down while the fix may still be an inexpensive connector or wiring repair rather than internal damage.