P28CF: Clutch A Pressure Sensor Circuit High

What it means

Voltage on the clutch A pressure sensor signal line is above the expected window. Wire shorted to B+ or sensor open.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

The clutch A pressure sensor reports hydraulic pressure to the TCM through a voltage signal. P28CF sets when that signal rises above the expected range, which can result from a short to battery voltage, an open sensor circuit, or a poor connector connection.

Common causes

Most likely first.

1. Signal wire shorted to B+
2. Open pressure sensor
3. Connector pins corroded - high contact resistance

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Record freeze-frame data and review live clutch A pressure sensor voltage to verify that the signal is above its expected range.
2. Inspect the sensor connector and harness for corrosion, loose terminals, or wiring damage that could interrupt the signal.
3. Using the manufacturer's wiring procedure, check whether the signal wire is shorted to battery voltage.
4. Check the sensor's supply and ground connections and test for an open circuit in the sensor path.
5. If the circuit is intact, test the clutch A pressure sensor itself against the manufacturer's specification.

Common fixes

• Repair a clutch A pressure sensor signal wire shorted to battery voltage.
• Restore an open or loose connection at the pressure sensor connector.
• Clean or replace corroded connector terminals.
• Replace the clutch A pressure sensor if it tests open or continues to produce an out-of-range high signal.

Can I keep driving?

Avoid extended driving because an incorrect pressure reading can lead to poor clutch engagement, slipping, or a transmission limp mode. Stop if the vehicle loses drive or shifts erratically.