P2721 indicates the powertrain control module has detected a higher-than-expected voltage on the control circuit for transmission pressure control solenoid D. This typically points to an open circuit, poor connection, or internal solenoid failure rather than a hydraulic problem. The code is electrical in nature and usually affects transmission line pressure control and shift quality.
A broken, chafed, or corroded wire in the solenoid D control circuit is the most common cause, producing the high-voltage condition the PCM detects.
The solenoid itself can develop an internal open coil or internal contact failure, causing the control circuit voltage to rise abnormally.
Poor pin contact, corrosion, or bent terminals at the transmission harness connector can interrupt the circuit and trigger a high-voltage reading.
A damaged, pushed-back, or corroded terminal at the PCM connector on the solenoid D circuit can produce the same high-voltage result.
The internal wiring inside the transmission connecting the external connector to solenoid D can chafe, corrode, or open due to fluid contamination and heat.
A failure of the driver circuit inside the PCM is possible but uncommon; it should only be considered after all wiring, connectors, and the solenoid are verified good.
Short distances may be possible, but the transmission may shift harshly or enter limp mode. Continued driving can cause clutch damage from improper line pressure, so diagnosis should not be delayed.
No. This is almost always an electrical circuit fault involving wiring, a connector, or a single solenoid. A full transmission replacement is rarely needed for this code.
Usually not. PCM driver failure is uncommon for this code. The vast majority of P2721 cases are caused by wiring, connector, or solenoid problems. Replacing the PCM without verifying those first is likely a waste of money.
Not by itself. Dirty fluid can contribute to solenoid contamination over time, but P2721 is a circuit-high code indicating an electrical fault. The wiring and solenoid must be diagnosed regardless of fluid condition.