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DTC codes / P07xx · Transmission / P0779

P0779Pressure Control Solenoid 'B' Intermittent

P0779 indicates that the transmission control module (TCM) has detected an intermittent fault in the circuit for pressure control solenoid 'B', which is used to regulate hydraulic pressure inside the automatic transmission. The TCM monitors the solenoid's electrical current and response, and it sets this code when the signal is erratic or drops out momentarily rather than failing completely.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms.
  • Harsh or delayed gear shifts, especially when the transmission is cold or under light throttle.
  • Intermittent slipping or flaring during upshifts or downshifts.
  • The transmission may occasionally enter limp mode (fail-safe mode) and stay in a single gear.
  • Rough engagement when shifting from park or neutral into drive or reverse.

Common causes, most likely first

  1. Faulty pressure control solenoid 'B' itself, with internal winding intermittency or sticking valves.
  2. Damaged, chafed, or corroded wiring in the solenoid circuit, often near heat sources or flex points.
  3. Loose or contaminated electrical connector at the solenoid or at the transmission case pass-through.
  4. Low or degraded transmission fluid, which can cause solenoid sticking and erratic pressure control.
  5. Valve body wear or debris blocking the solenoid's hydraulic circuit, leading to intermittent response.
  6. A failing transmission control module (TCM) or internal driver circuit, though this is less common.

How to diagnose and fix it

  1. Check transmission fluid level and condition; top off or replace fluid if it is low, dark, or smells burnt.
  2. Inspect the solenoid 'B' electrical connector and wiring for looseness, corrosion, or chafing, and repair as needed.
  3. Measure the resistance of solenoid 'B' at the transmission connector and compare it to the manufacturer's specification.
  4. Use a scan tool to command solenoid 'B' on and off while monitoring current and transmission response to confirm intermittent operation.
  5. Remove the transmission pan and inspect the solenoid 'B' for debris or sticking; clean or replace the solenoid if faulty.
  6. If the solenoid and wiring test good, inspect the valve body for wear or blockage that could affect pressure control.
  7. After repairs, clear the code and perform a relearn or adaptation drive cycle as required by the vehicle manufacturer.

Intermittent Solenoid Codes Can Mislead

  • An intermittent code like P0779 often does not mean the solenoid is completely failed; a poor connection or fluid issue can cause the same symptom without a hard part failure.
  • Technicians sometimes replace the solenoid only to find the real problem is a chafed wire inside the transmission harness that only shorts when the engine moves under load.
  • Debris from a failing torque converter or clutch material can lodge in the solenoid valve, causing intermittent sticking that mimics an electrical fault.
  • A low battery or charging system problem can cause the TCM to log false intermittent solenoid codes, so always check system voltage first.
  • After replacing a solenoid, some vehicles require a transmission adaptive relearn; skipping this step can leave the transmission shifting poorly and the code returning.

Can I keep driving with P0779?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because intermittent pressure control can cause harsh shifts or sudden limp mode. If the transmission slips severely or refuses to engage gears, stop driving and have it towed to prevent internal damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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