P0779 Pressure Control Solenoid "B" Intermittent

The P0779 trouble code is an OBD-II diagnostic trouble code related to the Pressure Control Solenoid "B" in an automatic transmission.

P0779 – Pressure Control Solenoid "B" Intermittent

This code means that the Transmission Control Module (TCM) has detected an intermittent or unstable electrical signal or operating condition involving Pressure Control Solenoid "B".

Pressure Control Solenoid "B" regulates transmission hydraulic pressure. The TCM changes the solenoid's operation according to driving conditions to control clutch engagement, gear changes and overall transmission pressure.

With P0779, the problem is not necessarily a permanently failed solenoid. The circuit may work normally at one moment and then become abnormal due to a loose connection, damaged wiring, internal solenoid fault, heat-related failure, contamination or another intermittent condition.

What Does P0779 Mean?

An automatic transmission relies on hydraulic pressure to apply internal clutches and control gear changes.

The TCM controls this pressure electronically using pressure-control solenoids.

The basic process is:

TCM → Pressure Control Solenoid "B" → Hydraulic Pressure → Clutch/Gear Operation

When the TCM commands Pressure Control Solenoid "B", it expects the electrical signal and resulting transmission behavior to remain within a predictable range.

If the signal or operation becomes unstable intermittently, the TCM may store:

P0779 – Pressure Control Solenoid "B" Intermittent

The word "intermittent" is particularly important. The fault may disappear during testing and return later, making this code more difficult to diagnose than a continuously present electrical fault.

What Is Pressure Control Solenoid "B"?

Pressure Control Solenoid "B" is an electrically controlled hydraulic valve used to regulate transmission fluid pressure.

Its exact function depends on the transmission design.

It may influence:

• Line pressure

• Clutch pressure

• Shift quality

• Clutch engagement

• Gear changes

• Torque converter operation

The TCM continuously adjusts the solenoid based on information such as:

• Engine load

• Throttle position

• Vehicle speed

• Engine RPM

• Transmission temperature

• Selected gear

• Input shaft speed

• Output shaft speed

What Does "Intermittent" Mean?

An intermittent fault means the problem does not remain continuously present.

For example, Pressure Control Solenoid "B" may work normally when the transmission is cold but develop an electrical problem when it becomes hot.

Another possibility is a connector that makes good contact most of the time but loses contact because of:

• Vibration

• Engine movement

• Heat

• Moisture

• Corrosion

• Loose terminals

This is why simply checking the solenoid once with a multimeter may not always find the problem.

Symptoms of P0779

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Intermittent harsh shifting

• Delayed gear changes

• Erratic shifting

• Transmission slipping

• Shift flare

• Sudden changes in shift firmness

• Transmission stuck in one gear

• Limp mode

• Reduced acceleration

• Poor fuel economy

• Increased transmission temperature

Some vehicles may have no noticeable symptoms when the fault is not active.

Common Causes of P0779

Loose or damaged electrical connector

An unstable connector can cause the solenoid signal to come and go.

Corroded connector terminals

Corrosion increases resistance and can cause intermittent electrical problems.

Damaged wiring

A wire that is partially broken may work normally until vibration or movement changes the connection.

Wiring that is rubbing against another component

Repeated vibration can damage insulation and create intermittent shorts.

Faulty Pressure Control Solenoid "B"

The solenoid may have an internal electrical fault that occurs only under certain conditions.

Heat-related solenoid failure

Some solenoids develop electrical problems as their internal temperature increases.

Transmission-fluid contamination

Dirty fluid can cause the solenoid to stick or respond inconsistently.

Low transmission fluid

Low fluid can cause unstable hydraulic pressure and abnormal transmission operation.

Incorrect transmission fluid

The wrong fluid can affect hydraulic performance and solenoid operation.

Valve-body problem

A sticking valve can create inconsistent pressure control.

Hydraulic pressure problem

A worn pump, internal leak or restricted passage can affect pressure regulation.

Low system voltage

Battery or charging-system problems can interfere with transmission solenoid operation.

Faulty TCM

A problem with the solenoid driver circuit inside the TCM is possible.

Is P0779 Serious?

P0779 can be serious, especially if the transmission is slipping or shifting harshly.

Because the problem is intermittent, the vehicle may appear to operate normally much of the time.

However, an intermittent pressure-control problem can suddenly produce:

• Incorrect clutch pressure

• Harsh shifts

• Clutch slip

• Excessive heat

If the problem is ignored, repeated slipping can contribute to internal transmission wear.

Can You Drive With P0779?

If the transmission is operating normally and the problem occurs only occasionally, a short trip to a repair facility may be possible.

However, avoid continued driving if you experience:

• Severe slipping

• Violent shifting

• Loss of drive

• Transmission overheating

• Repeated limp mode

• Major delays when selecting gears

An intermittent fault can become a permanent failure.

P0779 vs. P0778

These codes both involve Pressure Control Solenoid "B", but the fault type is different.

P0778 – Pressure Control Solenoid "B" Electrical

General electrical malfunction involving the solenoid circuit.

P0779 – Pressure Control Solenoid "B" Intermittent

The electrical signal or operation becomes abnormal intermittently.

If P0779 is stored, the technician should pay particular attention to loose connections, damaged wiring, vibration-related faults and temperature-dependent failures.

P0779 vs. P0777

P0777 – Pressure Control Solenoid "B" Stuck On

The system believes the solenoid is stuck in the commanded state or continuously active.

P0779 – Pressure Control Solenoid "B" Intermittent

The solenoid circuit or operation is unstable and the fault comes and goes.

P0779 vs. P0776

P0776 – Pressure Control Solenoid "B" Range / Performance

The solenoid is not operating within the expected range or performance parameters.

P0779 – Pressure Control Solenoid "B" Intermittent

The fault occurs intermittently rather than continuously.

P0779 vs. P0775

P0775 – Pressure Control Solenoid "B" Malfunction

A general malfunction involving the solenoid or its circuit.

P0779 – Pressure Control Solenoid "B" Intermittent

The control system specifically detects an intermittent condition.

Where Is Pressure Control Solenoid "B"?

The exact location depends on the transmission.

It may be:

• Inside the transmission

• Installed in the valve body

• Located underneath the transmission pan

• Integrated into a solenoid pack

• Integrated into a mechatronic assembly

Some transmissions allow individual solenoid replacement, while others require replacement of a complete solenoid pack or valve-body assembly.

How to Diagnose P0779

P0779 can be difficult to diagnose because the fault may disappear before the vehicle reaches the repair shop.

The diagnostic approach should focus on reproducing the intermittent condition.

1. Scan the TCM

Use a professional diagnostic scanner to retrieve:

• Stored codes

• Pending codes

• Freeze-frame data

• Transmission temperature

• Solenoid commands

• Transmission pressure data where available

Check for additional transmission codes.

2. Analyze freeze-frame data

Determine the conditions under which P0779 was stored.

Look at:

• Transmission temperature

• Vehicle speed

• Engine RPM

• Engine load

• Throttle position

• Selected gear

• Battery voltage

If the code was stored only when the transmission was hot, a temperature-related fault becomes more likely.

3. Inspect the connector

Carefully inspect the Pressure Control Solenoid "B" circuit.

Look for:

• Corrosion

• Loose terminals

• Bent pins

• Water intrusion

• Fluid contamination

• Damaged connector locks

4. Perform a wiring inspection

Check the complete harness for:

• Broken wires

• Chafing

• Pinched sections

• Melted insulation

• Poor repairs

• High resistance

• Intermittent continuity

Pay particular attention to areas exposed to engine vibration or heat.

5. Perform a wiggle test

An intermittent wiring problem may only appear when the harness moves.

With appropriate diagnostic equipment connected, carefully manipulate the harness and connectors while monitoring the circuit.

If the signal changes unexpectedly, the wiring or connector should be investigated.

6. Check electrical resistance

Measure the solenoid and circuit according to the manufacturer's specifications.

If possible, perform testing under different temperature conditions.

A solenoid that measures correctly when cold may develop an abnormal reading when hot.

7. Monitor the solenoid control signal

A professional scanner or oscilloscope can help determine whether the TCM's command is stable.

Look for:

• Missing commands

• Unexpected voltage changes

• Irregular PWM signals

• Sudden changes when the fault occurs

8. Check battery and charging voltage

Verify that system voltage is stable.

Electrical instability can affect the TCM and solenoid operation.

9. Inspect transmission fluid

Check:

• Fluid level

• Fluid condition

• Correct fluid specification

• Burnt odor

• Metal particles

• Clutch material

10. Check hydraulic pressure

If the electrical system appears normal, measure hydraulic pressure according to the manufacturer's procedure.

Compare pressure readings under different operating conditions.

11. Inspect the valve body

If the electrical circuit is functioning correctly but pressure control remains unstable, investigate:

• Sticking valves

• Worn valve bores

• Contamination

• Restricted passages

• Internal hydraulic leakage

12. Check for temperature-dependent behavior

Because P0779 is intermittent, compare operation:

• When cold

• At normal operating temperature

• After extended driving

A fault that appears only when hot can be a valuable diagnostic clue.

13. Check transmission speed data

Monitor:

• Input speed

• Intermediate shaft speed

• Output speed

Incorrect speed signals can influence TCM pressure and shift calculations.

14. Check the TCM

If the wiring, solenoid and hydraulic system all test correctly, the TCM's control circuit may need to be evaluated.

Can a Bad Solenoid Cause P0779?

Yes.

Pressure Control Solenoid "B" can develop an internal fault that occurs only under certain conditions.

For example, its resistance may change as the solenoid heats up.

Can Wiring Cause P0779?

Yes, and wiring should be taken seriously with an intermittent code.

A partially broken wire may maintain contact most of the time but lose continuity when the vehicle vibrates.

Can a Bad Connector Cause P0779?

Yes.

A loose or corroded connector is a common type of intermittent electrical problem.

Can Dirty Transmission Fluid Cause P0779?

Yes.

Contaminated fluid can cause the solenoid or valve body to stick intermittently.

Can Low Transmission Fluid Cause P0779?

It can contribute to abnormal pressure control.

Low fluid can cause unstable hydraulic pressure and shift problems.

However, an electrical circuit fault should not be dismissed simply because the fluid level is low.

Can a Bad Valve Body Cause P0779?

Yes.

A sticking or worn valve can cause pressure to fluctuate or respond incorrectly.

This can produce intermittent transmission symptoms.

Can P0779 Cause Harsh Shifting?

Yes.

Pressure Control Solenoid "B" affects hydraulic pressure, so an unstable signal can cause inconsistent shift firmness.

Can P0779 Cause Transmission Slipping?

Yes.

Incorrect pressure can prevent a clutch from applying with enough force, potentially resulting in slip.

Can P0779 Cause Limp Mode?

Yes.

The TCM may enter a protective operating strategy if pressure control becomes unreliable.

Can P0779 Cause Transmission Overheating?

Yes, potentially.

Repeated clutch slip can generate additional heat.

Can P0779 Damage the Transmission?

The code itself does not prove internal damage.

However, continued operation with repeated pressure-control problems or clutch slip can accelerate transmission wear.

Can P0779 Be Caused by the TCM?

Yes, but the TCM should normally be considered only after the external circuit and transmission components have been tested.

Before replacing the TCM, verify:

Connector → Wiring → Solenoid → Fluid → Valve Body → Hydraulic Pressure → TCM

Common Diagnostic Mistakes With P0779

Replacing the solenoid immediately

An intermittent wiring problem can produce the same code.

Testing the vehicle only when cold

Some intermittent faults appear only after the transmission reaches operating temperature.

Ignoring the connector

A loose terminal can be the entire cause of the problem.

Performing only a static resistance test

A solenoid can pass a cold resistance test but fail when hot.

Ignoring the wiring harness

Vibration-related wiring problems are particularly important with intermittent codes.

Assuming the problem is purely hydraulic

P0779 can be caused by an electrical fault.

Replacing the TCM too early

The complete circuit should be tested before condemning the control module.

What Is the Correct Repair for P0779?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Repairing damaged wiring

• Replacing damaged connector terminals

• Repairing loose connections

• Cleaning connector corrosion

• Repairing water intrusion

• Replacing Pressure Control Solenoid "B"

• Correcting transmission-fluid level

• Repairing transmission-fluid leaks

• Replacing contaminated or incorrect transmission fluid

• Servicing the valve body

• Repairing hydraulic pressure problems

• Repairing internal transmission components

• Updating TCM software

• Reprogramming the TCM

• Replacing the TCM when confirmed defective

How to Test the Vehicle After Repair

Because P0779 is intermittent, the post-repair test should be more thorough than a simple short drive.

Verify that:

• Solenoid "B" responds consistently

• The electrical signal remains stable

• Wiring does not lose continuity during movement

• Connector terminals remain secure

• Hydraulic pressure remains within specification

• Gear changes are consistent

• No slipping occurs

• Transmission temperature remains normal

• Limp mode does not activate

• No additional transmission codes return

• P0779 does not return

The vehicle should ideally be tested under the conditions that originally triggered the code.

Frequently Asked Questions About P0779

What does P0779 mean?

P0779 means the transmission control system has detected an intermittent problem involving Pressure Control Solenoid "B" or its control circuit.

Does P0779 mean the solenoid is bad?

No. Wiring, connectors, transmission fluid, valve-body problems, hydraulic pressure issues and the TCM can also be responsible.

Why is P0779 difficult to diagnose?

Because the fault is intermittent and may disappear during testing.

Can a loose connector cause P0779?

Yes.

Can damaged wiring cause P0779?

Yes. A partially broken or chafed wire can cause an intermittent connection.

Can dirty transmission fluid cause P0779?

Yes. Contaminated fluid can cause a solenoid or valve to stick intermittently.

Can low transmission fluid cause P0779?

It can contribute to unstable hydraulic operation, but the electrical circuit should still be checked.

Can P0779 cause harsh shifting?

Yes.

Can P0779 cause slipping?

Yes.

Can P0779 cause limp mode?

Yes, depending on the vehicle.

Can P0779 cause overheating?

Yes. Repeated clutch slip can increase transmission temperature.

Can I drive with P0779?

A short trip may be possible if the transmission is operating normally. If there is severe slipping, overheating, violent shifting or loss of drive, continued driving should be avoided.

Does P0779 mean the transmission needs replacement?

No. The problem should be diagnosed before considering major transmission repair or replacement.

Final Thoughts on P0779

P0779 – Pressure Control Solenoid "B" Intermittent indicates that the transmission control system has detected an unstable or intermittent condition involving Pressure Control Solenoid "B".

Because the fault is intermittent, diagnosis should focus heavily on wiring, connectors, temperature-dependent failures and vibration-related electrical problems.

The recommended diagnostic sequence is:

Scan Data → Freeze-Frame → Connector → Wiring → Wiggle Test → Solenoid → Fluid → Hydraulic Pressure → Valve Body → TCM

A faulty pressure-control solenoid is possible, but it should not be replaced automatically. A loose connector, damaged harness, contaminated fluid or valve-body problem can produce very similar symptoms.

If the transmission is slipping, shifting violently or overheating, the vehicle should not continue to be driven unnecessarily. Early diagnosis can prevent an intermittent pressure-control problem from developing into more serious transmission damage.