P0788: Shift Timing Solenoid A High

What it means

Shift timing solenoid A control circuit reads stuck high — short to battery voltage or open coil/return.

At a glance

• Usually lights the check-engine light

How it works

The TCM controls Shift Timing Solenoid A through an electrical circuit and monitors the circuit’s response. P0788 sets when the circuit is detected at a high electrical level, which can result from a wire shorted to battery voltage, an open solenoid coil, or a related connection fault.

Common causes

Most likely first.

1. Control wire shorted to battery voltage
2. Open solenoid coil

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. Review freeze-frame data and related codes to determine when the high-circuit fault occurred and whether other solenoids are affected.
2. Inspect Shift Timing Solenoid A wiring and connector for damage, loose pins, corrosion, or contact with a power feed.
3. Check the solenoid coil and control circuit for an open or short to battery voltage using the manufacturer’s wiring diagram and specifications.
4. Separate the solenoid from the vehicle-side circuit as directed by service information to determine whether the open or high reading is in the coil, wiring, or connector.
5. If the solenoid and harness test correctly, test the TCM output and grounds according to the manufacturer’s procedure.

Common fixes

• Reconnect, clean, or repair loose or corroded Shift Timing Solenoid A terminals.
• Repair wiring shorted to battery voltage or an open in the solenoid control circuit.
• Replace Shift Timing Solenoid A if its coil is open.
• Repair the TCM output fault only after wiring and solenoid tests confirm the module is responsible.

Can I keep driving?

Limit driving if shifting is harsh, delayed, or slipping, and avoid towing or hard acceleration because the circuit fault can prevent normal shift timing. If the transmission shifts unpredictably or loses drive, stop safely and arrange assistance.