What Does P0778 Mean?
The TCM has detected an electrical fault in the Pressure Control Solenoid B circuit. The circuit has abnormal resistance, an open, or a short condition that prevents the TCM from properly controlling the solenoid. Without proper electrical control, the solenoid cannot regulate transmission line pressure, leading to shift quality problems or limp mode activation.
Common Causes
35%
Failed PCS B solenoid (internal coil open or short circuit)
25%
Damaged wiring harness between TCM and transmission (broken, chafed, or corroded wires)
20%
Corroded or damaged transmission connector causing high resistance
12%
TCM solenoid driver circuit failure
8%
Poor ground connection at TCM or transmission case
Diagnostic Steps
1
Measure PCS B solenoid resistance at the transmission connector — compare to manufacturer spec (typically 4-8 ohms for variable force solenoids).
2
Inspect the transmission external connector for water damage, corrosion, bent or pushed-back pins, and proper seal integrity.
3
Check for proper voltage supply and ground at the solenoid when commanded on by the TCM using a multimeter.
4
Perform a wiggle test on the entire harness from TCM to transmission connector while monitoring continuity of the PCS B circuit.
5
If external wiring is good, remove the solenoid and test it directly with a bench power supply to isolate an internal coil failure.
6
Check TCM output pins for proper PWM signal using an oscilloscope if solenoid and wiring test normal.
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The TCM has detected an electrical fault in the Pressure Control Solenoid B circuit. The circuit has abnormal resistance, an open, or a short condition that prevents the TCM from properly controlling the solenoid. Without proper electrical control, the solenoid cannot regulate transmission line pres...
The most common cause of P0778 (Pressure Control Solenoid B Electrical) is: Failed PCS B solenoid (internal coil open or short circuit)
Typical repair costs for P0778 range from $150 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The transmission will likely enter limp mode, restricting the vehicle to a single gear. Driving is possible at low speeds but highway driving becomes impractical. Have the electrical fault repaired promptly to restore normal transmission operation.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0778 to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
