What does it mean?
P1720 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Pressure Control, Shift Control, TCC Solenoid Circuit Malfunction .
Symptoms
- MIL on with a transmission warning light
- Transmission stuck in limp mode with one fixed gear
- No torque converter lock-up and high engine speed at cruise
- Harsh, banging or completely missing gear changes
- Vehicle unable to move in some selector positions
- Overheating smell from the transmission fluid
Likely causes
- Lost common supply voltage to the solenoid pack from a blown fuse, a failed relay or a broken feed wire
- Corroded or fluid-contaminated transmission case connector affecting several circuits at once
- Damaged internal transmission harness or lead frame
- One solenoid shorted to ground, dragging the shared supply down with it
- Failed solenoid pack or valve body assembly
- Poor transmission module supply or ground
- Low, burnt or contaminated fluid making the solenoids stick in their bores
How to fix it
- Check fluid level, colour and smell before starting any electrical work
- Confirm the solenoid supply voltage and its fuse or relay first, since one shared feed explains all three circuits at once
- Measure each solenoid winding resistance at the case connector and compare with specification
- Look for a single circuit shorted to ground that could be pulling the shared supply down
- Inspect the case connector and internal harness for fluid intrusion, corrosion and pushed-out pins
- Check transmission module power and ground quality with voltage drop tests
- Replace the solenoid pack or internal harness if several windings are out of specification, and service the filter and fluid