P0799 – Pressure Control Solenoid “C” Intermittent

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: General | Location: Designator C

Definition source: SAE J2012/J2012DA (industry standard)

P0799 is a powertrain diagnostic trouble code that indicates an intermittent condition involving Pressure Control Solenoid “C.” “Intermittent” means the fault is not present all the time; it may appear and disappear due to vibration, heat, moisture, harness movement, or a solenoid that occasionally sticks or loses electrical continuity. Because transmission designs, solenoid labeling, and monitoring strategies vary by vehicle, the exact enabling conditions, failure criteria, and related symptoms can differ. Use the vehicle’s service information to confirm solenoid identification, connector pinouts, circuit routing, and the exact tests required. Treat P0799 as a detected intermittent behavior in the solenoid/circuit/control system until proven by test results.

What Does P0799 Mean?

P0799 means the control module has detected an intermittent issue associated with Pressure Control Solenoid “C.” Based strictly on the official definition, the fault is characterized by an on-and-off (non-continuous) condition rather than a steady “high,” “low,” or “open” electrical state. In practical diagnostic terms, the module is seeing a pressure-control-solenoid-related signal or control behavior that is unstable or inconsistent compared to what it expects during the monitor. SAE J2012 defines the DTC structure, while the specific “Solenoid C” naming and how intermittency is detected (feedback strategy, calculated pressure response, or electrical observation) can vary by vehicle and must be verified in service information.

Quick Reference

• Subsystem: Automatic transmission pressure control system; Pressure Control Solenoid “C” circuit/control.
• Common triggers: Intermittent electrical connection, harness movement/vibration, heat-related coil interruption, connector fluid intrusion/corrosion, or an intermittently sticking solenoid affecting commanded pressure behavior.
• Likely root-cause buckets: Wiring/connector issues, solenoid internal fault, power/ground or shared feed issues, hydraulic/mechanical influences that mimic intermittency, control module/driver or calibration (varies by vehicle).
• Severity: Often moderate to high; may cause shift quality problems and protective operating modes, with potential to affect drivability.
• First checks: Confirm fluid condition/level per service info, inspect transmission connector(s) and harness routing, check for loose pins/poor terminal tension, scan data review for when the fault sets.
• Common mistakes: Replacing the solenoid immediately without proving an intermittent connection, skipping wiggle/heat testing, or ignoring shared power/ground and connector contamination.

Theory of Operation

Pressure control solenoids regulate hydraulic pressure in the transmission by modulating fluid flow through internal passages. The control module commands Pressure Control Solenoid “C” to adjust line pressure or apply pressure for specific clutch circuits, depending on transmission design. The solenoid is typically controlled electrically (often with a modulated command) so pressure can be adjusted smoothly as operating conditions change.

To determine whether the system is operating correctly, the module compares commanded solenoid operation to expected outcomes. Depending on vehicle design, this may involve monitoring the electrical behavior of the solenoid circuit/driver and/or evaluating transmission response using available sensor inputs and calculated pressure/shift behavior. P0799 sets when the observed behavior becomes inconsistent in an intermittent way—working normally at times, then deviating—often linked to unstable electrical continuity, marginal terminals, or a solenoid that intermittently fails to respond.

Symptoms

• Shift quality: Harsh, delayed, or inconsistent upshifts/downshifts that come and go.
• Slip flare: Momentary engine rpm flare during shifts or under load, intermittent.
• Limp mode: Reduced shifting strategy or failsafe operation that may reset after a key cycle.
• Warning lamp: Check engine or transmission warning indicator illuminated intermittently.
• Driveability: Hesitation or abnormal acceleration feel related to unexpected gear or pressure changes.
• Engagement: Intermittent delayed engagement when shifting into drive or reverse.
• Fuel economy: Noticeable, intermittent decrease in efficiency due to abnormal shift scheduling/pressure control.

Common Causes

• Connector/terminal intermittency: Loose pin fit, fretting, light corrosion, or a partially seated connector at the pressure control solenoid “C” or the transmission harness pass-through.
• Harness damage: Chafed, pinched, or heat-damaged wiring that intermittently opens or shorts when the drivetrain moves or when temperature changes.
• Internal harness/lead issues: Intermittent connection within the transmission internal wiring to solenoid “C” (varies by vehicle design).
• Pressure control solenoid “C” intermittently sticking or dropping out: Electrical coil connection or mechanical response that is inconsistent under certain temperatures or duty cycles (must be verified by testing).
• Power/ground instability: Momentary loss of solenoid feed power or ground path due to shared splices, ground points, or high resistance that changes with vibration.
• Transmission fluid contamination affecting solenoid operation: Debris or degraded fluid that can contribute to inconsistent hydraulic response; not confirmed by the DTC alone.
• Control module driver/command issue: Intermittent output driver behavior or logic response (rare; consider after verifying circuits and solenoid integrity).
• Related sensor input intermittency: A fluctuating pressure-related or speed-related input that leads the module to flag the solenoid “C” command/response as intermittent (monitoring strategy varies by vehicle).

Diagnosis Steps

Tools that help include a scan tool with transmission live-data and bidirectional controls (if supported), a digital multimeter, a back-probing kit, and basic hand tools for connector access. A wiring diagram and connector pinout from service information are essential. If available, use a breakout lead or test harness to reduce terminal damage during testing.

1. Confirm the complaint and capture data: Scan for DTCs and record freeze-frame and any pending codes. Note transmission-related symptoms and whether the code sets during specific conditions (cold start, hot soak, bumps, certain gears). Clear codes only after saving this information.
2. Check for companion DTCs and prioritization: If other transmission electrical, power supply, or ground-related codes are present, diagnose those first because they can create intermittent behavior that triggers P0799.
3. Visual inspection (external): With ignition off, inspect the transmission harness routing, clips, and loom. Look for rub-through, pinched sections, fluid contamination at connectors, and signs of overheating. Correct obvious harness routing issues before deeper testing.
4. Connector integrity checks: Unplug and inspect the solenoid/harness connectors (as applicable) for bent pins, pushed-out terminals, moisture, corrosion, or poor terminal tension. Reseat connectors fully and ensure secondary locks are engaged. If terminals are suspect, service/replace terminals per service information.
5. Wiggle test with live monitoring: With the scan tool monitoring relevant transmission data (and solenoid “C” command/feedback PIDs if available), gently wiggle the harness at likely stress points (near connectors, brackets, crossmembers, and pass-through areas). Watch for glitches, dropouts, or sudden changes that coincide with movement.
6. Circuit checks for intermittent opens/shorts: Using the wiring diagram, check continuity of the solenoid “C” control and feed circuits end-to-end. While testing, flex the harness and tap lightly near connectors to reproduce intermittency. If continuity changes or is unstable, isolate by segment to find the fault location.
7. Voltage-drop testing under load: With the circuit powered and the solenoid commanded (bidirectional control) or during operating conditions when the code typically sets, perform voltage-drop tests on the solenoid feed and ground/control paths. Excessive drop or an unstable reading indicates high resistance, poor terminal contact, or shared splice/ground issues. Consult service information for method and acceptance criteria.
8. Solenoid “C” functional verification: If bidirectional controls are available, command pressure control solenoid “C” through its range and observe whether commanded changes correlate with available pressure/shift behavior indicators in live data (varies by vehicle). Inconsistent response suggests a solenoid, hydraulic issue, or circuit intermittency; continue isolating before replacing parts.
9. Check power and ground stability for the control system: Verify stable module power supply and ground paths, especially if multiple actuators share a feed or ground point. Perform voltage-drop checks across main grounds and any shared splices while loading the system (lights, blower, or commanded solenoids as applicable) to reveal intermittent supply issues.
10. Assess transmission fluid condition (supporting check): Inspect fluid level/condition per service procedures. Contaminated or degraded fluid can contribute to inconsistent solenoid/hydraulic behavior, but do not treat this as proof of the DTC cause without correlating evidence from tests and symptoms.
11. Decision point and verification: If wiring/connector faults are found, repair and secure the harness, then clear codes and road test while logging live data. If circuits are proven stable and the issue persists, follow service information for solenoid “C” testing/replacement steps and any required adaptation/relearn procedures.

Professional tip: Intermittent solenoid-related codes are often caused by terminal tension issues that look “clean” on inspection. If the code sets on bumps or during drivetrain movement, prioritize pin-fit checks and loaded voltage-drop testing over static resistance measurements, then confirm the repair with an extended road test and live-data logging under the same conditions that originally triggered the fault.

Possible Fixes & Repair Costs

Repair costs for P0799 vary widely because the code only indicates an intermittent condition involving Pressure Control Solenoid “C”. The final scope depends on pinpoint testing results, required parts access, fluid condition, harness repairs, and labor time based on vehicle layout.

• Repair wiring/connector issues: Clean, secure, and repair loose terminals, corrosion, damaged insulation, pin fit concerns, or chafing found in the solenoid “C” circuit.
• Restore power/ground integrity: Correct poor grounds, shared ground faults, or power feed issues confirmed by voltage-drop testing under load.
• Service transmission fluid and filter: If service information supports it and contamination/incorrect fluid is verified, correct fluid level/condition and replace filter as applicable to reduce erratic pressure control behavior.
• Replace Pressure Control Solenoid “C”: Replace only after confirming the solenoid intermittently fails electrically or mechanically (for example, abnormal command response or intermittent coil behavior).
• Repair internal harness/connector: On designs with internal transmission wiring, repair/replace the internal harness or pass-through connector if intermittency is confirmed there.
• Module update or replacement (as verified): If all external and internal circuit checks pass and the intermittent fault can be correlated to control-module output/driver behavior, follow service information for reprogramming or module testing/replacement steps.

Can I Still Drive With P0799?

You may be able to drive cautiously for a short distance if the vehicle operates normally, but an intermittent pressure control solenoid condition can quickly change shift quality and drivability. If you notice harsh or delayed shifts, slipping, reduced-power behavior, warning messages, or any situation where the vehicle cannot maintain speed predictably, avoid driving and arrange service. If any safety-related warnings appear (such as brake or steering warnings), or if the vehicle stalls, will not move, or enters a severe limp mode, do not drive.

What Happens If You Ignore P0799?

Ignoring P0799 can lead to repeated intermittent shift problems, worsening drivability, and increased heat and wear within the transmission due to unstable line pressure control. Over time, this may contribute to accelerated clutch or band wear, fluid degradation, and more expensive repairs, especially if the underlying cause is a harness fault that progressively deteriorates.

Related Pressure Solenoid Codes

Compare nearby pressure solenoid trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0749 – Pressure Control Solenoid “A” Intermittent
• P0779 – Pressure Control Solenoid “B” Intermittent
• P0764 – Shift Solenoid “C” Intermittent
• P0759 – Shift Solenoid “B” Intermittent
• P0754 – Shift Solenoid “A” Intermittent
• P0748 – Pressure Control Solenoid “A” Electrical

Key Takeaways

• P0799 indicates intermittency involving Pressure Control Solenoid “C”, not a guaranteed failed part.
• Most efficient fixes start with basics: connectors, harness routing, and power/ground integrity under load.
• Capture the failure: live-data logging and wiggle testing are often necessary to reproduce an intermittent condition.
• Fluid condition matters: verify level and condition per service information because pressure control stability can be affected.
• Confirm before replacing: replace the solenoid or internal harness only after test results point there.

Vehicles Commonly Affected by P0799

• Vehicles with electronically controlled automatic transmissions that use multiple pressure control solenoids.
• High-mileage vehicles where harness flexibility, terminal tension, and connector seals may be degraded.
• Vehicles exposed to heat and vibration near the transmission case, leading to intermittent circuit contact.
• Vehicles used for stop-and-go driving where frequent shifting increases solenoid duty cycles.
• Vehicles operated in wet or corrosive environments that can promote connector corrosion or water intrusion.
• Vehicles with prior transmission service where connectors may be partially seated or wiring may be pinched during reassembly.
• Vehicles with underbody damage that may have disturbed transmission wiring routing or brackets.
• Vehicles with aftermarket electrical accessories that may introduce shared ground or power disturbances.

FAQ

Does P0799 mean Pressure Control Solenoid “C” is bad?

No. P0799 means an intermittent condition was detected for Pressure Control Solenoid “C”. Intermittent faults are commonly caused by wiring, connector pin fit, corrosion, power/ground instability, or an internal harness issue. Replace the solenoid only after testing confirms it intermittently fails or does not respond correctly to commanded control.

Can low or dirty transmission fluid cause P0799?

It can contribute, depending on vehicle design and how pressure control is monitored. Incorrect fluid level or contaminated fluid may cause unstable pressure regulation that can make control behavior appear intermittent. Verify fluid level and condition strictly per service information and fix any confirmed issues, but do not assume fluid is the only cause without circuit and solenoid testing.

Why does the code come and go?

P0799 is an intermittent fault by definition, so it may set only when the problem occurs during certain temperatures, vibration levels, or operating conditions. Common reasons include loose terminals, chafed wiring that intermittently touches metal, moisture intrusion, or an internal connection that opens momentarily. Capturing data during the event and performing a wiggle test are often key to finding it.

What tests help confirm the root cause?

Helpful tests include a thorough connector inspection (terminal tension and corrosion), wiggle testing while monitoring live data, voltage-drop testing on power and ground circuits under load, and continuity checks when the fault is present. If supported, commanding the solenoid on/off with a scan tool and logging related pressure or shift behavior can help identify whether the issue is electrical, hydraulic, or control-related.

Will clearing P0799 fix it?

Clearing the code only resets the warning and monitor status; it does not correct the intermittent condition. If the underlying issue remains, P0799 is likely to return when the same operating conditions occur. The correct approach is to verify the fault with testing, repair the confirmed cause, and then confirm the repair with a road test and a complete monitor rerun per service information.

After repairs, confirm the fix by verifying stable solenoid “C” command/response and circuit integrity during a road test that recreates the conditions that originally triggered P0799.