P0787: Shift Timing Solenoid A Low

What it means

Shift timing solenoid A control circuit reads stuck low — short to ground or low-side driver stuck on.

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. P0787 sets when that control circuit is detected at a low electrical level, which can result from a short to ground, a shorted solenoid coil, or a control-driver fault.

Common causes

Most likely first.

1. Short to ground in the solenoid control wiring
2. Shift Timing Solenoid A coil shorted internally
3. Damaged connector or corroded terminals
4. Fault in the transmission control module driver

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. Read freeze-frame data and related codes to determine when the low-circuit fault occurred and whether other solenoid circuits are affected.
2. Inspect Shift Timing Solenoid A’s connector and harness for chafing, crushed insulation, corrosion, fluid intrusion, or a wire touching ground.
3. Check the solenoid coil and circuit for a short to ground using the manufacturer’s wiring diagram and electrical specifications.
4. Disconnect the solenoid as directed by the service information and determine whether the low reading remains in the vehicle-side wiring or follows the solenoid.
5. If the wiring and coil test correctly, test the TCM driver and its grounds according to the manufacturer’s procedure.

Common fixes

• Clean and secure corroded or loose Shift Timing Solenoid A connector terminals.
• Repair wiring shorted to ground in the solenoid control circuit.
• Replace Shift Timing Solenoid A if its coil is internally shorted.
• Repair the TCM driver only if circuit testing confirms the module is at fault.

Can I keep driving?

Because a low solenoid control circuit can disrupt shift timing, drive only as needed and avoid towing or hard acceleration. If shifts become harsh, slipping, or unpredictable, stop safely; continued operation can worsen transmission damage.