Wiring fault on the solenoid control circuit, such as a short to voltage or chafed loom; Damaged, corroded or loose connector at the solenoid or internal transmission harness; Faulty shift timing solenoid A (internal electrical fault); Low or contaminated transmission fluid affecting the solenoid or valve body; Fault in the transmission control module driver circuit; Low or unstable system voltage from a weak battery or charging fault; Outdated or faulty transmission control software, where the manufacturer lists it as a known cause for the model.

P0788

Shift Timing Solenoid A High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
88: FaultThe specific fault in that area

What it means

P0788 means the transmission control module has detected a high voltage or a circuit fault on the control circuit of shift timing solenoid A. The module compares the commanded state of the solenoid circuit with the voltage it actually measures, and sets the code when the reading is higher than expected. The exact layout and the solenoid's role vary by transmission, so check the manufacturer data for the specific model.

Symptoms

Malfunction indicator lamp or transmission warning lamp on
Harsh, delayed or flared gear changes
Transmission stuck in one gear (limp mode)
Poor fuel economy
Gearbox not shifting at the expected points
Reduced performance or restricted engine power

Possible causes

Wiring fault on the solenoid control circuit, such as a short to voltage or chafed loomlikely
Damaged, corroded or loose connector at the solenoid or internal transmission harnesslikely
Faulty shift timing solenoid A (internal electrical fault)likely
Low or contaminated transmission fluid affecting the solenoid or valve bodypossible
Fault in the transmission control module driver circuitpossible
Low or unstable system voltage from a weak battery or charging faultpossible
Outdated or faulty transmission control software, where the manufacturer lists it as a known cause for the modelrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting when the fault set, then check for related solenoid or communication codes
Check the transmission fluid level, condition and smell, following the manufacturer procedure for the model
Test battery condition and charging voltage, as low or unstable voltage can upset solenoid readings
Visually inspect the wiring and connectors between the control module and the transmission for chafing, heat damage, corrosion and water ingress
Check the solenoid circuit for short to voltage, open circuit and correct resistance against the manufacturer wiring diagram and specification
Measure the solenoid winding resistance and compare it with the specification for that transmission
Use a scan tool to command the solenoid and watch for the expected response, if the model supports this
Check for applicable service bulletins or software updates for the vehicle before replacing the control module

How to fix

Repair or replace damaged wiring and clean or replace faulty connectors
Replace the shift timing solenoid A if its resistance or operation is out of specification
Correct the fluid level or change the fluid and filter if it is contaminated, as the manufacturer recommends
Repair the battery or charging system fault if voltage is unstable
Replace or repair the transmission control module only after the wiring and solenoid are proven good
Apply a manufacturer software update if an outdated calibration is a known cause for the model

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but the gearbox may go into limp mode and shift harshly. Have it checked soon, as continued driving can cause extra wear or transmission damage.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.