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DTC codes / P07xx · Transmission / P0799

P0799Pressure Control Solenoid 'C' Intermittent

P0799 indicates that the transmission control module has detected an intermittent electrical fault in the pressure control solenoid 'C' circuit, which is responsible for regulating hydraulic pressure inside the automatic transmission. The computer monitors the solenoid's electrical current and sees it momentarily drop out or spike outside the expected range, but the fault is not continuous, so the code sets only when the irregularity repeats within a short drive cycle.

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 engagements, especially when shifting from park to drive or reverse.
  • Intermittent slipping or flaring during upshifts, particularly under light throttle.
  • The transmission may enter limp mode (stuck in a single gear) after the fault repeats.
  • Occasional shudder or vibration during steady-speed driving when the solenoid momentarily fails.

Common causes, most likely first

  1. A failing pressure control solenoid 'C' with an internally worn coil or sticking valve.
  2. Damaged, chafed, or corroded wiring in the solenoid circuit, often near heat sources or flex points.
  3. Loose or contaminated electrical connector pins at the solenoid or transmission case pass-through.
  4. Transmission fluid that is degraded, low, or contaminated with debris, causing intermittent solenoid sticking.
  5. A faulty transmission control module (TCM) or internal driver circuit that intermittently loses connection.
  6. Poor ground connection for the transmission or TCM, leading to voltage fluctuations in the solenoid circuit.

How to diagnose and fix it

  1. Check the transmission fluid level and condition; top off or replace fluid if it is low or burnt.
  2. Inspect the solenoid 'C' wiring harness and connector for chafing, corrosion, or loose pins, and repair as needed.
  3. Measure the resistance of solenoid 'C' at the transmission connector and compare it to the manufacturer's specification.
  4. Perform a wiggle test on the harness while monitoring solenoid resistance or live data to catch intermittent opens.
  5. If resistance is out of spec or the solenoid fails a functional test, replace the pressure control solenoid 'C'.
  6. Clear the code and perform a relearn or adaptation drive cycle to verify the repair and ensure the fault does not return.
  7. If the fault persists after electrical checks, diagnose the TCM and its ground circuits for intermittent faults.

Intermittent Solenoid Faults Often Misdiagnosed

  • A intermittent code like P0799 is frequently caused by a poor connection rather than a failed solenoid, so a thorough wiggle test of the harness and connector is essential before condemning the part.
  • Debris in the transmission fluid can cause the solenoid valve to stick only under certain pressure conditions, producing an intermittent fault that disappears after a fluid change.
  • The code can set from a momentary voltage drop caused by a failing alternator or battery, so checking charging system stability is a smart first step on high-mileage vehicles.
  • Many technicians replace the solenoid only to find the real problem is a chafed wire inside the transmission pan, so always inspect the internal harness when the pan is off.
  • P0799 does not always mean the solenoid is failing; a sticking valve body or low fluid pressure can mimic the same intermittent electrical signature.

Can I keep driving with P0799?

You can usually continue driving to a repair shop, but avoid heavy acceleration or towing until the fault is repaired, because intermittent pressure control can cause harsh shifts and, in some cases, leave the transmission in limp mode without warning.

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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