P0797 Pressure Control Solenoid "C" Stuck On

The P0797 trouble code is an OBD-II diagnostic trouble code related to the Pressure Control Solenoid "C" inside an automatic transmission.

P0797 – Pressure Control Solenoid "C" Stuck On

This code means that the transmission control module (TCM) or powertrain control module (PCM) has detected that Pressure Control Solenoid "C" is remaining in an activated or "on" condition when the transmission expects it to be off or operating differently.

The solenoid regulates hydraulic pressure inside the transmission. If it remains activated, hydraulic pressure may not correspond to the pressure commanded by the TCM.

This can result in:

• Harsh shifting

• Delayed gear changes

• Incorrect gear engagement

• Transmission slipping

• Limp mode

• Increased transmission temperature

P0797 does not automatically mean that the entire transmission is damaged. The cause can be electrical, hydraulic, mechanical, or related to the solenoid itself.

What Does P0797 Mean?

An automatic transmission uses hydraulic pressure to control its internal clutches, brakes and gearsets.

The TCM controls this pressure through electronically operated solenoids.

The simplified process is:

TCM → Pressure Control Solenoid "C" → Hydraulic pressure → Clutch/gear operation

Under normal conditions, the TCM changes the solenoid's operation according to driving conditions.

If the TCM commands the solenoid to reduce or stop its operation but the system continues to behave as though the solenoid is activated, it may store:

P0797 – Pressure Control Solenoid "C" Stuck On

The exact function of Solenoid "C" varies by transmission. It should not be assumed that it controls the same clutch, gear or pressure circuit in every vehicle.

What Is a Pressure Control Solenoid?

A pressure control solenoid is an electrically controlled hydraulic valve.

Its purpose is to regulate transmission pressure.

The TCM can control the solenoid according to:

• Engine load

• Throttle position

• Vehicle speed

• Engine RPM

• Selected gear

• Transmission temperature

• Input shaft speed

• Output shaft speed

Correct pressure is essential for smooth and reliable gear changes.

If pressure is too high, shifts can become harsh.

If pressure is too low, clutches may slip.

What Does "Stuck On" Mean?

"Stuck On" does not necessarily mean that the solenoid is physically jammed in one position.

It can indicate that the control system is detecting a condition consistent with the solenoid remaining activated.

Possible reasons include:

• Solenoid mechanically stuck

• Electrical circuit shorted

• Solenoid internally damaged

• Valve body contamination

• Incorrect hydraulic pressure

• TCM control problem

• Wiring fault

Therefore, P0797 should not automatically be diagnosed as a physically stuck solenoid.

Symptoms of P0797

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Harsh shifting

• Hard engagement into Drive

• Hard engagement into Reverse

• Delayed shifting

• Incorrect shift timing

• Transmission slipping

• Gear flare

• Transmission stuck in one gear

• Reduced acceleration

• Poor fuel economy

• Transmission overheating

• Limp mode

• Reduced transmission performance

Some vehicles may initially have only a warning light.

Common Causes of P0797

Stuck Pressure Control Solenoid "C"

The solenoid valve may be physically stuck in the activated position.

Contaminated transmission fluid

Dirt, clutch material or metal particles can interfere with solenoid movement.

Valve body contamination

Contamination inside the valve body can prevent the solenoid or associated valve from moving correctly.

Faulty solenoid

The solenoid may have an internal mechanical or electrical failure.

Shorted control circuit

The solenoid may continuously receive an electrical command because of a short circuit.

Damaged wiring

A damaged wire can cause incorrect solenoid activation.

Corroded connector

Corrosion can change circuit resistance or create an unintended electrical connection.

Incorrect transmission fluid

The wrong fluid can affect hydraulic operation and valve movement.

Low-quality or degraded fluid

Old fluid may contain deposits that interfere with valve-body operation.

Valve-body wear

Worn valve bores can cause hydraulic pressure to behave incorrectly.

Hydraulic pressure problem

A pressure-control issue elsewhere in the transmission can create conditions interpreted as a solenoid problem.

Faulty TCM

A failed TCM driver circuit may continuously command the solenoid.

Low system voltage

Electrical problems can affect solenoid operation and TCM control.

Is P0797 Serious?

Yes, P0797 should be taken seriously.

The pressure-control solenoid directly influences transmission hydraulic pressure.

If the transmission cannot regulate pressure correctly, continued driving may cause:

• Clutch wear

• Excessive heat

• Harsh engagement

• Incorrect gear operation

• Internal transmission damage

The seriousness depends on the actual symptoms and the transmission design.

Can You Drive With P0797?

It is generally better to avoid unnecessary driving when P0797 causes noticeable transmission symptoms.

If the vehicle is shifting normally and only the warning light is present, a short trip to a repair facility may be possible.

However, avoid driving if you experience:

• Severe slipping

• Very harsh shifts

• Loss of drive

• Transmission overheating

• Transmission stuck in a gear

• Severe delay when selecting Drive or Reverse

A transmission that is slipping or operating with incorrect pressure can deteriorate quickly.

P0797 vs. P0796

These codes are closely related.

P0796 – Pressure Control Solenoid "C" Performance or Stuck Off

Indicates a performance problem or a condition where Solenoid "C" may be stuck off.

P0797 – Pressure Control Solenoid "C" Stuck On

Indicates that the control system believes Solenoid "C" is remaining activated.

The distinction is important because the diagnostic direction can be different.

P0797 vs. P0798

P0797 – Pressure Control Solenoid "C" Stuck On

The system believes the solenoid is remaining activated.

P0798 – Pressure Control Solenoid "C" Electrical

The system has detected an electrical problem in the solenoid circuit.

A P0798 diagnosis should focus heavily on the electrical circuit.

A P0797 diagnosis should consider:

Solenoid operation + hydraulic pressure + valve body + electrical control

P0797 vs. P0799

P0799 – Pressure Control Solenoid "C" Intermittent

The problem occurs intermittently.

P0797 – Pressure Control Solenoid "C" Stuck On

The system detects a persistent or sustained activated condition.

Where Is Pressure Control Solenoid "C"?

The exact location depends on the transmission.

It may be:

• Inside the valve body

• Inside the transmission

• Integrated into a mechatronic unit

• Part of a transmission control valve assembly

Access may require removing the transmission pan and, on some transmissions, additional components.

Always identify the solenoid using the vehicle-specific transmission wiring diagram and service documentation.

How to Diagnose P0797

Because P0797 can be caused by both electrical and hydraulic problems, diagnosis should cover both areas.

1. Scan all control modules

Use a professional scan tool capable of communicating with the TCM.

Look for additional codes involving:

• Other pressure-control solenoids

• Transmission pressure

• Gear ratio

• Input/output speed

• Transmission temperature

• TCM communication

• System voltage

Additional codes can help identify the root cause.

2. Check freeze-frame data

Record:

• Engine RPM

• Vehicle speed

• Selected gear

• Throttle position

• Transmission temperature

• Battery voltage

Determine under what conditions the code was set.

3. Check live transmission data

Monitor:

• Commanded solenoid state

• Actual pressure if available

• Line pressure

• Gear command

• Input speed

• Output speed

Compare commanded values with actual behavior.

4. Inspect the transmission connector

Look for:

• Corrosion

• Bent pins

• Loose terminals

• Water intrusion

• Oil contamination

5. Inspect the wiring

Check the harness for:

• Broken wires

• Chafing

• Pinched wiring

• Melted insulation

• Short circuits

• Previous repairs

6. Check the solenoid control circuit

Determine whether the solenoid is receiving a continuous electrical command when it should not.

A short to power or a failed control driver can cause continuous activation.

7. Test solenoid resistance

Measure the resistance of Pressure Control Solenoid "C" according to the manufacturer's procedure.

Compare the measurement with the factory specification.

Do not rely on a generic resistance value because transmission solenoids differ considerably.

8. Perform an actuator test

If supported, command Solenoid "C" on and off using the diagnostic scanner.

Check whether the solenoid responds correctly.

If the scanner commands the solenoid off but the electrical circuit remains active, investigate the control circuit.

9. Check transmission fluid

Inspect the fluid for:

• Correct level

• Correct fluid specification

• Excessive discoloration

• Burnt odor

• Clutch material

• Metal particles

• Contamination

Fluid inspection should follow the manufacturer's procedure.

10. Inspect the valve body

If the electrical circuit and solenoid appear correct, inspect the valve body.

Look for:

• Sticking valves

• Contamination

• Deposits

• Worn valve bores

• Damaged passages

A sticking valve can create a "stuck on" condition even when the electrical circuit is working correctly.

11. Check hydraulic pressure

Perform a pressure test if required.

Compare actual pressure with the manufacturer's specifications for the relevant gear and operating conditions.

Incorrect pressure can help distinguish a solenoid problem from a broader hydraulic fault.

12. Check the transmission filter

If the transmission uses a serviceable filter, inspect it for excessive debris.

A heavily contaminated filter may indicate internal wear or fluid contamination.

13. Check TCM operation

If the solenoid and wiring are correct but the TCM continues to command the solenoid incorrectly, investigate the TCM.

Can a Bad Solenoid Cause P0797?

Yes.

A defective Pressure Control Solenoid "C" can become mechanically stuck or fail internally.

Contamination is also capable of preventing the solenoid from moving correctly.

Can Wiring Cause P0797?

Yes.

A shorted control circuit can continuously activate the solenoid.

This is especially important when the solenoid itself passes resistance and functional tests.

Can Dirty Transmission Fluid Cause P0797?

Yes, potentially.

Contaminated fluid can cause a solenoid or valve-body component to stick.

However, the electrical control circuit should still be checked because P0797 can also result from an electrical problem.

Can Low Transmission Fluid Cause P0797?

Low fluid can cause hydraulic pressure problems and abnormal shifting.

However, low fluid alone does not necessarily mean that the solenoid is electrically or mechanically stuck on.

If P0797 is present, both the electrical and hydraulic systems should be evaluated.

Can P0797 Cause Harsh Shifting?

Yes.

If Solenoid "C" maintains excessive or incorrect hydraulic pressure, shifts can become:

• Hard

• Abrupt

• Delayed

• Unpredictable

Can P0797 Cause Transmission Slipping?

It can.

Incorrect pressure control can cause clutch engagement problems.

Whether slipping occurs depends on which hydraulic circuit Solenoid "C" controls.

Can P0797 Cause Limp Mode?

Yes.

The TCM may activate a protective operating strategy when it detects a serious pressure-control problem.

The transmission may then remain in a limited gear range.

Can P0797 Damage the Transmission?

Potentially, yes.

Incorrect hydraulic pressure can cause abnormal clutch engagement and excessive heat.

If the transmission is slipping or shifting violently, continued driving may increase internal wear.

Can P0797 Be Caused by the TCM?

Yes, but the TCM should not be the first suspect.

A failed output driver can continuously command the solenoid.

Before replacing the TCM, verify:

Power → Ground → Wiring → Connector → Solenoid → Control signal → Hydraulic operation

Common Diagnostic Mistakes With P0797

Replacing the transmission immediately

P0797 does not automatically mean that the transmission must be rebuilt or replaced.

Replacing the solenoid without testing the control circuit

A shorted wire or TCM driver can cause continuous activation.

Changing the fluid and assuming the problem is solved

Fluid service cannot repair an electrical short or failed solenoid.

Ignoring the valve body

A sticking valve can produce symptoms similar to a continuously activated solenoid.

Using generic solenoid resistance values

Always use the manufacturer's specification.

Replacing the TCM too quickly

The complete circuit and solenoid should be tested first.

What Is the Correct Repair for P0797?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Replacing Pressure Control Solenoid "C"

• Repairing a shorted control circuit

• Repairing damaged wiring

• Repairing connector terminals

• Cleaning corrosion

• Repairing water intrusion

• Restoring proper power and ground

• Cleaning the valve body

• Repairing or replacing worn valve-body components

• Replacing a contaminated transmission filter

• Correcting transmission-fluid level

• Using the correct transmission fluid

• Repairing the mechatronic assembly

• Updating TCM software

• Reprogramming the TCM

• Replacing the TCM when confirmed defective

If internal transmission damage is discovered, additional repair may be necessary.

How to Test the Vehicle After Repair

After repairing P0797, verify:

• Solenoid "C" responds correctly

• Solenoid resistance is within specification

• Control circuit operates correctly

• No short circuit remains

• Connector is secure

• Transmission pressure is within specification

• Valve-body operation is normal

• Transmission fluid level is correct

• Gear changes are smooth

• No slipping occurs

• Transmission does not enter limp mode

• P0797 does not return

A complete road test should be performed under different operating conditions.

Frequently Asked Questions About P0797

What does P0797 mean?

P0797 means the transmission control system has detected that Pressure Control Solenoid "C" appears to be stuck in an activated condition.

Does P0797 mean the transmission is bad?

No. The cause may be a solenoid, wiring problem, valve-body problem, hydraulic issue or TCM fault.

Can a bad solenoid cause P0797?

Yes.

Can wiring cause P0797?

Yes. A shorted control circuit can continuously activate the solenoid.

Can dirty transmission fluid cause P0797?

Yes. Contamination can cause the solenoid or valve body to stick.

Can P0797 cause harsh shifting?

Yes. Incorrect hydraulic pressure can cause hard or abrupt shifts.

Can P0797 cause transmission slipping?

Yes, depending on the hydraulic circuit controlled by Solenoid "C".

Can P0797 cause limp mode?

Yes.

Can I drive with P0797?

If there are significant transmission symptoms, continued driving should be avoided. If the vehicle operates normally, a short trip for diagnosis may be possible.

Does P0797 require transmission replacement?

No. The solenoid, wiring, valve body and hydraulic system should be diagnosed before considering major transmission repair.

Final Thoughts on P0797

P0797 – Pressure Control Solenoid "C" Stuck On indicates that the transmission control system believes Pressure Control Solenoid "C" is remaining activated when it should not be.

The correct diagnostic path should consider both electrical and hydraulic causes:

Wiring → Connector → Solenoid → Control signal → Transmission fluid → Valve body → Hydraulic pressure → TCM

This is different from P0798, which specifically identifies an electrical fault, and P0799, which indicates an intermittent condition.

The most important point is that P0797 does not automatically mean the transmission needs to be replaced.

A faulty solenoid, shorted wire, contaminated valve body, sticking hydraulic valve or TCM control problem can all produce the code.

If the vehicle is experiencing hard shifting, severe slipping, delayed engagement or transmission overheating, avoid unnecessary driving and diagnose the problem promptly. Early diagnosis can prevent a relatively small solenoid or valve-body problem from developing into expensive internal transmission damage.