P2840: Shift Fork D Position Circuit

What it means

The TCM cannot read a valid position signal from shift fork D position sensor. Selector engagement state is unknown.

At a glance

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

How it works

Shift fork D moves an internal transmission selector, and its position sensor supplies the TCM with feedback about the fork's position. P2840 sets when the TCM cannot obtain a valid fork D circuit signal, leaving it unable to reliably confirm selector engagement.

Common causes

Most likely first.

1. Position sensor failed
2. Wiring or connector fault

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. Save freeze-frame data and read TCM live data for fork D position and circuit status to determine whether the signal is absent, unstable, or invalid only during a shift.
2. Inspect the fork D sensor, connector, and harness for loose or damaged terminals, corrosion, broken wires, or fluid intrusion.
3. Check the fork D sensor supply and ground, then measure its signal and continuity against the manufacturer's specification.
4. Test the harness between the fork D sensor and TCM for opens or shorts using the vehicle wiring diagram and service procedure.
5. If the wiring and power checks pass, test the fork D position sensor and replace it only if it fails the specified test.

Common fixes

• Reconnect or clean the fork D sensor connector and correct damaged terminals.
• Repair an open or shorted section of fork D sensor wiring.
• Replace a fork D position sensor that fails testing.

Can I keep driving?

Avoid driving if shifts are harsh, slipping, or missing, or if the transmission is locked in one gear; the TCM cannot confirm fork D position and may restrict operation. If symptoms are mild or absent, keep driving to a minimum until diagnosed.