If a car has no drive in any range with the fluid level okay, what is the likely cause?

In this scenario, if a car has no drive in any range but the fluid level is confirmed to be okay, very low oil pressure is indeed a likely cause. The automatic transmission relies on hydraulic pressure generated by the pump to engage the gears and operate the clutches effectively. If the oil pressure is insufficient, it will prevent the system from functioning correctly, ultimately resulting in a lack of engagement in any gear.

Low oil pressure can stem from various issues, such as pump wear, internal leaks, or blockage in the fluid passages that inhibit the hydraulic system from developing the necessary pressure to operate the transmission. When these conditions arise, the transmission may exhibit symptoms like slippage or complete loss of drive, which aligns with the situation described in the question.

Other possibilities, like worn components or issues specifically with the torque converter, could also contribute to similar symptoms, but would typically involve additional signs or specific operating conditions not indicated here. Thus, low oil pressure stands out as the most straightforward explanation for the loss of drive across all ranges.