P0799 Pressure Control Solenoid "C" Intermittent

The P0799 – Pressure Control Solenoid "C" Intermittent diagnostic trouble code (DTC) indicates that the transmission control module (TCM) has detected an intermittent or unstable condition in the electrical or operating circuit of Pressure Control Solenoid "C."

Pressure control solenoids are responsible for regulating hydraulic pressure inside an automatic transmission. The TCM uses these solenoids to control clutch packs, bands, valves, and gear changes.

With P0799, the solenoid may operate correctly most of the time but occasionally produce an abnormal response, lose its electrical connection, stick, or fail to regulate pressure as commanded.

P0799 does not automatically mean that the transmission needs to be rebuilt or replaced. The problem can originate from the solenoid, wiring, connector, transmission fluid, valve body, hydraulic system, or control system.

What Does P0799 Mean?

The code can be understood as:

• P – Powertrain-related fault

• 07 – Transmission-related control system

• 99 – Pressure control solenoid circuit

• Solenoid "C" – A manufacturer-designated pressure control solenoid

• Intermittent – The fault occurs periodically rather than continuously

In simple terms:

P0799 means the transmission control system is intermittently detecting a problem with Pressure Control Solenoid "C" or its control circuit.

What Is Pressure Control Solenoid "C"?

A pressure control solenoid is an electronically controlled valve that regulates hydraulic pressure.

The transmission uses hydraulic pressure to operate various internal components, including:

• Clutch packs

• Bands

• Shift valves

• Torque-converter functions

• Hydraulic circuits

The TCM controls the solenoid by varying its electrical command.

The exact function of Solenoid C is manufacturer-specific. It does not have the same physical location or function in every transmission.

Therefore, the transmission's wiring diagram and hydraulic circuit documentation are important when diagnosing P0799.

Why Is Transmission Pressure Important?

Automatic transmissions depend on precise hydraulic pressure.

Too little pressure can cause:

• Clutch slipping

• Delayed engagement

• Poor gear changes

• Excessive clutch wear

Too much pressure can cause:

• Harsh shifts

• Abrupt engagement

• Increased mechanical stress

The pressure control solenoid allows the TCM to adjust hydraulic pressure according to driving conditions.

What Does "Intermittent" Mean?

The word intermittent is particularly important with P0799.

The solenoid circuit may work normally for several minutes or several driving cycles and then suddenly become abnormal.

The fault could occur because of:

• Internal solenoid failure

• Loose connector

• Damaged wiring

• Corroded terminal

• Solenoid sticking

• Contaminated transmission fluid

• Valve-body problem

• Excessive temperature

• Internal transmission pressure problem

This can make P0799 more difficult to diagnose than a permanent electrical fault.

Symptoms of P0799

Symptoms depend on the transmission and the severity of the problem.

Possible symptoms include:

Harsh shifting

Gear changes may become noticeably harder or more abrupt.

Delayed shifting

The transmission may take longer than normal to change gears.

Erratic shifting

Shift quality may change unpredictably.

Transmission slipping

The engine RPM may rise without a corresponding increase in vehicle speed.

Delayed Drive or Reverse engagement

The vehicle may take several seconds to engage a gear.

Transmission limp mode

The TCM may restrict transmission operation.

Check Engine Light

The MIL may illuminate.

Transmission warning message

Some vehicles display a dedicated transmission warning.

Poor acceleration

Incorrect hydraulic pressure can interfere with normal gear operation.

Can P0799 Cause Transmission Slipping?

Yes.

If Pressure Control Solenoid C controls hydraulic pressure for a clutch or another transmission circuit, an intermittent pressure-control problem can cause insufficient pressure.

When pressure is too low, a clutch pack may not hold firmly.

This can produce:

• RPM flare

• Slipping

• Delayed engagement

• Excessive heat

However, actual clutch wear can produce similar symptoms, so the solenoid should not automatically be blamed.

Can P0799 Cause Harsh Shifting?

Yes.

An intermittent pressure-control problem can cause hydraulic pressure to become higher or lower than intended.

This can result in:

• Hard 1-2 shifts

• Harsh downshifts

• Abrupt engagement

• Shift hesitation

The specific gears affected depend on what Solenoid C controls in that particular transmission.

Can P0799 Cause Limp Mode?

Yes.

If the TCM cannot reliably control hydraulic pressure, it may place the transmission into a protective operating mode.

Depending on the vehicle, this can result in:

• Limited gears

• Fixed gear operation

• Disabled manual mode

• Higher line pressure

• Reduced vehicle performance

Is P0799 a Serious Problem?

It can be.

An intermittent pressure-control fault should not be ignored.

If the transmission continues operating with incorrect hydraulic pressure, prolonged slipping or harsh operation can generate additional heat and accelerate clutch wear.

The severity is greater if you notice:

• Transmission slipping

• Loss of Drive

• Delayed engagement

• Severe shift shock

• Limp mode

• Transmission fluid overheating

Common Causes of P0799

Faulty Pressure Control Solenoid C

The solenoid may have an internal electrical or mechanical problem.

Solenoid sticking

Contamination can prevent the valve from moving freely.

Damaged wiring

The circuit may have an intermittent open or short.

Loose connector

Vibration can temporarily interrupt the electrical connection.

Corroded terminals

Corrosion can increase resistance and cause an unstable signal.

Contaminated transmission fluid

Dirty or degraded fluid can interfere with solenoid and valve-body operation.

Low transmission fluid

Insufficient fluid can cause hydraulic pressure problems.

Valve-body problem

A sticking or worn valve can produce pressure-control problems even when the solenoid itself is functional.

Internal transmission leakage

Worn seals or hydraulic passages can cause pressure loss.

Electrical power problem

Unstable voltage can affect solenoid operation.

TCM fault

A control-module problem is possible but should normally be considered after the solenoid and circuit have been tested.

Can Low Transmission Fluid Cause P0799?

Yes, potentially.

A low fluid level can cause:

• Reduced hydraulic pressure

• Aeration

• Delayed engagement

• Erratic shifting

• Solenoid-control problems

However, the fluid level must be checked according to the manufacturer's procedure.

Some transmissions require the fluid to be checked at a specific temperature with the engine running and the selector in a specified position.

Can Dirty Transmission Fluid Cause P0799?

Yes.

Contaminated fluid can affect the operation of a pressure-control solenoid.

Debris may cause the solenoid or valve-body components to stick.

Transmission fluid that is:

• Very dark

• Burnt-smelling

• Contaminated with debris

• Heavily degraded

can be an important diagnostic clue.

However, fluid condition alone does not prove that Solenoid C has failed.

Can a Bad Connector Cause P0799?

Yes.

Because this code is intermittent, the connector deserves particular attention.

Inspect for:

• Loose terminals

• Corrosion

• Water intrusion

• Bent pins

• Damaged locking mechanisms

• Poor terminal tension

A connector that loses contact momentarily can cause the TCM to detect an intermittent solenoid fault.

Can Wiring Cause P0799?

Yes.

Inspect the wiring between the TCM and Pressure Control Solenoid C.

Look for:

• Open circuits

• Intermittent opens

• Short circuits

• Chafing

• Pinched wires

• High resistance

• Damaged insulation

Because the fault is intermittent, moving the harness while monitoring the circuit can sometimes help locate the problem.

Can a Bad Solenoid Cause P0799?

Yes.

The solenoid may have:

• Internal coil failure

• Intermittent electrical contact

• Mechanical sticking

• Contamination

• Incorrect resistance

• Slow response

A solenoid can sometimes test normally when cold and fail when hot.

Can Heat Cause P0799?

Yes.

Transmission components operate in a demanding temperature environment.

An electrical component that works correctly when cold may develop a fault as its temperature increases.

If P0799 occurs after extended driving or heavy traffic, compare solenoid operation when cold and hot.

Can a Valve Body Cause P0799?

Yes.

The pressure control solenoid works together with the valve body.

A worn or sticking valve can cause hydraulic pressure to behave incorrectly even if the solenoid itself is electrically healthy.

Possible valve-body problems include:

• Sticking valves

• Worn valve bores

• Internal leakage

• Contamination

• Damaged passages

Can P0799 Be Caused by a Worn Transmission?

Possibly.

Internal transmission wear can cause pressure-control problems.

For example, worn seals or clutch components can create hydraulic leakage.

However, P0799 alone should not be interpreted as proof of internal transmission failure.

Start with the simpler possibilities:

Fluid → Wiring → Connector → Solenoid → Valve Body → Hydraulic Pressure → Internal Transmission

How Is P0799 Diagnosed?

A systematic diagnosis is important because the fault is intermittent.

1. Scan all modules

Check for additional transmission codes.

Other solenoid, pressure, gear-ratio, or communication codes can provide important clues.

2. Check transmission fluid

Verify the correct level and inspect fluid condition.

3. Inspect the solenoid circuit

Check wiring and connectors.

4. Monitor live data

Look at commanded and actual transmission pressure if the vehicle provides this information.

5. Monitor solenoid operation

Check whether Solenoid C responds correctly to commands.

6. Test electrical resistance

Compare the solenoid resistance with the manufacturer's specification.

7. Check power and control circuits

Verify that the solenoid receives the correct electrical command.

8. Perform a hydraulic pressure test

If necessary, measure transmission pressure according to the manufacturer's procedure.

9. Inspect the valve body

If electrical tests pass but pressure remains abnormal, investigate the hydraulic system.

10. Road test

Monitor the transmission while reproducing the conditions under which the fault occurs.

How Do You Test Pressure Control Solenoid C?

The exact test depends on the transmission.

A technician may perform:

Resistance test

Measure the solenoid coil resistance and compare it with factory specifications.

Power test

Verify that the solenoid receives the correct electrical supply.

Control-signal test

Check the TCM's command to the solenoid.

Actuation test

Use a diagnostic scanner to command the solenoid when supported.

Hydraulic pressure test

Determine whether the solenoid actually produces the expected pressure response.

An electrical resistance test alone is not always sufficient.

A solenoid can have correct resistance but still stick mechanically.

What Resistance Should Solenoid C Have?

There is no universal resistance value for P0799.

Different transmissions use different solenoid designs and specifications.

Always compare the measured value with the manufacturer's specification.

Temperature should also be considered because electrical resistance changes with temperature.

What If the Solenoid Tests Good?

A solenoid can pass a basic electrical test and still cause P0799.

In that situation, investigate:

• Intermittent wiring

• Connector terminals

• TCM control signal

• Valve-body operation

• Hydraulic pressure

• Fluid contamination

• Mechanical sticking

The problem may only occur under operating temperature or hydraulic load.

What If P0799 Appears Only When the Transmission Is Hot?

This is an important clue.

Possible causes include:

• Solenoid thermal failure

• Wiring resistance

• Connector expansion

• Fluid viscosity changes

• Valve-body sticking

• Internal hydraulic leakage

The system should be tested under the temperature conditions in which the fault occurs.

What If P0799 Appears During Acceleration?

If the code appears during acceleration, transmission pressure demand may be increasing.

The system may be unable to maintain the required pressure.

Check:

• Solenoid operation

• Commanded pressure

• Actual pressure

• Fluid level

• Fluid condition

• Hydraulic leakage

What If P0799 Appears During Gear Changes?

Monitor the transmission during the specific shift where the fault occurs.

If the problem is always associated with one particular shift, determine which clutch or hydraulic circuit Solenoid C controls on that transmission.

This information can significantly narrow the diagnosis.

Can P0799 Cause a Transmission Overheat?

It can contribute to overheating.

If pressure is incorrect and a clutch pack slips, friction can generate additional heat.

Continued operation with severe slipping can accelerate transmission damage.

Can P0799 Cause a Burning Smell?

Potentially.

If the fault results in clutch slipping, transmission fluid may overheat and develop a burnt odor.

A burnt smell combined with slipping should be taken seriously.

What If P0799 Appears With Other Solenoid Codes?

Multiple solenoid codes can point toward a common problem such as:

• Low system voltage

• TCM power problem

• Transmission connector issue

• Shared wiring fault

• Fluid contamination

• Valve-body problem

If several solenoid codes appear simultaneously, replacing each solenoid individually may be the wrong approach.

What If P0799 Appears Alone?

If P0799 is the only transmission code, begin with the circuit and Solenoid C.

Check:

Fluid → Connector → Wiring → Solenoid → Control signal → Hydraulic pressure

An isolated P0799 often provides a more focused diagnostic path.

Common Diagnostic Mistakes

Replacing the transmission immediately

P0799 does not automatically indicate internal transmission failure.

Replacing the solenoid without checking wiring

An intermittent harness or connector can cause the same code.

Checking resistance only

A solenoid can have correct resistance but still stick mechanically.

Ignoring fluid level

Low fluid can cause hydraulic pressure problems.

Ignoring the valve body

The valve body can cause pressure-control problems even when the solenoid is functional.

Clearing the code without reproducing the fault

An intermittent problem may return later.

How Is P0799 Repaired?

The repair depends on the confirmed cause.

Possible repairs include:

• Replacing Pressure Control Solenoid C

• Repairing damaged wiring

• Replacing connector terminals

• Cleaning or repairing electrical connections

• Correcting transmission fluid level

• Replacing contaminated fluid when appropriate

• Servicing the valve body

• Repairing hydraulic pressure problems

• Repairing internal transmission components when confirmed

• Performing TCM-related procedures when required

• Replacing the TCM only after proper diagnosis

Does P0799 Mean the Transmission Needs to Be Rebuilt?

No.

P0799 alone is not enough evidence to justify a transmission rebuild.

The problem may be a relatively simple electrical or solenoid issue.

Before considering major internal repairs, check:

• Fluid level

• Fluid condition

• Wiring

• Connectors

• Solenoid C

• TCM command

• Valve body

• Hydraulic pressure

Only confirmed internal wear or damage should lead to major transmission repair.

Can You Drive With P0799?

It depends on the symptoms.

If the transmission shifts normally and the code is intermittent, a short drive to a repair facility may be possible.

However, continued driving is not recommended if you experience:

• Severe slipping

• Delayed engagement

• Hard shifting

• Loss of Drive

• Transmission overheating

• Limp mode

• Burning transmission-fluid smell

Continued operation while the transmission is slipping can cause significantly more damage.

How to Reset P0799

Simply clearing P0799 does not repair the problem.

The correct process is:

Diagnose → Repair → Clear DTC → Verify solenoid operation → Road test → Rescan

Because P0799 is intermittent, the road test should reproduce the operating conditions under which the code originally appeared.

Final Thoughts on P0799

P0799 – Pressure Control Solenoid "C" Intermittent indicates that the transmission control system has detected an intermittent problem involving Pressure Control Solenoid C or its control circuit.

The main diagnostic path is:

Transmission Fluid → Connector → Wiring → Solenoid C → TCM Control Signal → Valve Body → Hydraulic Pressure → Internal Transmission

Common causes include a failing or sticking solenoid, damaged wiring, loose or corroded connectors, contaminated or low transmission fluid, valve-body problems, hydraulic pressure loss, or an intermittent control-module issue.

Because this is an intermittent code, simply measuring the solenoid once may not reveal the problem. Temperature, vibration, harness movement, and transmission operating conditions can all influence the fault.

Most importantly, P0799 does not automatically mean the transmission needs to be replaced or rebuilt.

A sensible diagnostic sequence is:

Scan all codes → Check fluid level and condition → Inspect wiring/connectors → Monitor Solenoid C → Test power and control circuit → Test solenoid → Check hydraulic pressure → Inspect valve body if necessary → Repair confirmed fault → Clear code → Road test → Rescan.