What Does P0788 Mean?
The TCM has detected that the Shift Timing Solenoid A circuit voltage or current is above the expected threshold. A high signal typically indicates a short circuit to power, a short to ground in the solenoid coil (reducing resistance and increasing current), or a wiring issue that is feeding excessive voltage to the circuit. This causes the solenoid to be over-energized, potentially disrupting shift timing.
Common Causes
30%
Shift timing solenoid A with internally shorted coil windings (low resistance)
25%
Wiring short to battery voltage in the solenoid circuit
20%
Wiring short to ground on the control side, pulling excessive current
15%
Damaged connector allowing cross-pin contact between circuits
10%
TCM driver circuit malfunction outputting excessive voltage
Diagnostic Steps
1
Measure shift timing solenoid A resistance — a reading significantly lower than specification indicates shorted coil windings.
2
Disconnect the solenoid and check the harness for shorts to battery voltage using a multimeter.
3
Check for shorts to ground on the solenoid control wire with the solenoid disconnected.
4
Inspect the transmission connector for damaged insulation between pins, contamination, or cross-pin shorts.
5
If the solenoid and wiring test normal, measure the TCM output voltage with an oscilloscope to verify it is within specification.
6
Check for recently performed repairs that may have damaged the harness or introduced a routing issue near heat sources.
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
The TCM has detected that the Shift Timing Solenoid A circuit voltage or current is above the expected threshold. A high signal typically indicates a short circuit to power, a short to ground in the solenoid coil (reducing resistance and increasing current), or a wiring issue that is feeding excessi...
The most common cause of P0788 (Shift Timing Solenoid A High) is: Shift timing solenoid A with internally shorted coil windings (low resistance)
Typical repair costs for P0788 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An over-energized solenoid can cause abnormal shift timing and potentially damage the solenoid coil through overheating. The vehicle is drivable but shifts may be erratic. Repair promptly to prevent solenoid burnout and further electrical damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0788 to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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