P0968: Pressure Control Solenoid "C" Control Circuit/Open

P0968 reports an open circuit on a third pressure control solenoid. Before anything else, it is worth saying what makes this code different from its 'A' and 'B' equivalents: the part it refers to is not a given.

The SAE numbering defines slots for pressure control solenoids up to 'C', but a transmission only sets this code if it has one. Plenty of four and five speed automatics manage with two, and will never store P0968 under any circumstances. Where a third does exist, it tends to be the most specialised of the group, because the first two have already taken the general jobs — mainline pressure for 'A', a principal clutch circuit for 'B'. What is left for 'C' varies enormously by design: converter clutch apply pressure on a great many transmissions, a specific band or clutch used only in the upper ratios on others, and on some later units a circuit that only participates under particular temperature or load conditions.

So the first and highest-value step on this code is not electrical. It is establishing what 'C' actually controls on that specific transmission, from the manufacturer's own documentation. Everything downstream depends on it — what symptom you should expect, what the driver should be asked about, how urgent the fault is, and in some cases which connector the circuit even runs through, because on certain transmissions the third solenoid is fed separately from the first two rather than sharing their case pass-through.

The most common answer, and the one that produces the least obvious symptoms, is torque converter apply pressure. If that is what 'C' does on a given vehicle, an open circuit means the converter clutch never locks. And a car with no converter lockup does not shift badly. It behaves in a way most owners do not associate with the transmission at all: engine revs sit several hundred rpm higher than usual at a steady motorway cruise, fuel consumption goes up noticeably, and the transmission runs hotter because all the drive is going through fluid coupling instead of a mechanical connection. The complaints that arrive at a workshop are 'it is drinking fuel', 'it feels busy on the motorway', or 'the transmission temperature warning came on while towing'. Nobody says the gearbox is broken, and the check engine light gets attributed to something else.

That is worth taking seriously rather than filing as a mild inconvenience. Losing lockup on a car that does regular motorway miles is a real and continuous fuel penalty, and the heat is the more damaging part. A converter that never locks dumps its slip losses straight into the transmission fluid, and sustained high fluid temperature shortens the life of the friction material, the seals and the remaining solenoids. The fault is not dramatic day to day and it is quietly expensive over months.

The electrical diagnosis itself follows the familiar shape — the module's intelligent driver reports it can find no load, so the question is whether the break is inside the transmission or outside it, and a coil resistance measurement at the case pass-through connector answers that in one step. What differs is the economics of the repair when the break turns out to be internal. On several transmission families the third solenoid is the least accessible of the group, positioned deepest in the valve body or behind the pump, which means labour rather than parts dominates the bill. That inverts the usual advice about whether to replace one solenoid or the whole pack. When the labour to reach a $200 part is most of a day, fitting the complete pack while the transmission is open is frequently the cheaper decision over the life of the car, and it is a conversation worth having before the work starts rather than after.