OBD-II trouble code
P0797: Pressure Control Solenoid "C" Stuck On
The module can turn this circuit on and cannot turn it off. That is a loss of authority rather than a loss of function — and it gives you a decisive test the stuck-off code does not have: take the command away and see whether anything changes.
Quick facts
- System
- Powertrain
- Category
- Transmission / Pressure Control
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $1,400
- DIY difficulty
- Shop recommended
What does P0797 mean?
P0797 and P0796 are often treated as two flavours of the same fault, and they are not. Stuck off leaves a circuit sitting in its de-energised state, which is the state the transmission is designed to fall back to when everything is switched off. Stuck on leaves a circuit commanded in a way the module cannot cancel. That is a different kind of failure: the module has not lost a function, it has lost authority. Whatever this pressure circuit is doing, it will keep doing regardless of what the controller wants, and the transmission has to operate around it.
That difference produces the single most useful test on this code, and it is one the stuck-off code cannot offer. If the fault is genuinely stuck on, taking the command away changes nothing. De-energise the solenoid — command it off with a scan tool, or disconnect it — and watch the pressure. If pressure drops when the solenoid loses its command, then it was not stuck at all and the fault is in the control side: a driver stage in the module holding the circuit energised, or a signal wire shorted to power keeping it alive whatever the module intends. If pressure stays exactly where it was with the solenoid electrically dead, the valve is stuck mechanically and the solenoid is innocent of everything except being attached to a fouled bore. Two very different repairs, separated by one measurement.
The onset history is also worth asking about, because it tends to differ from the stuck-off pattern. Stuck-off faults usually creep in as varnish accumulates, so the complaint starts as an occasional oddity and gradually becomes constant. Stuck-on faults are more often abrupt — a piece of debris arriving at a valve and wedging it, or an output driver failing short. An owner who says it was completely fine on Tuesday and wrong on Wednesday is describing something that arrived rather than something that wore in, and that shifts the suspicion toward debris and toward the electrical driver.
As with its sibling, what the symptom feels like depends on whether this transmission uses normally-high or normally-low pressure control solenoids, so establish that before interpreting the complaint. And as with every code in this family, the code names a behaviour rather than a part: low fluid, a clogged filter, a scored bore and contamination can all hold a valve where it should not be, with a perfectly good solenoid bolted to it.
Common causes
- Debris wedged in the valve bore holding the spool in its applied position
- Solenoid seized internally, unable to return when the command is removed
- Module output driver failed short, keeping the solenoid energised regardless of command
- Control wire shorted to a power feed, energising the solenoid independently of the module
- Varnish or scoring in the bore preventing the return spring from moving the spool
- Broken or fatigued return spring inside the solenoid
- Contaminated fluid carrying debris into the valve body after wear elsewhere
- Valve body damage from a previous repair or from a dropped valve during service
Symptoms
- Shift quality wrong in a consistent direction that does not change with driving style or load
- Harsh, slamming engagement or persistent slipping, depending on whether the solenoid is normally high or normally low
- Transmission behaving identically whether the fault is commanded on or off, which is characteristic
- Symptom that appeared suddenly rather than gradually worsening
- Transmission overheating
- Limp mode holding a fixed ratio
- Check engine light with P0797 stored, often with P0700 alongside
- Engagement into drive or reverse feeling abrupt
Diagnostic steps
- 1.Ask how it started. A sudden onset points at debris or at an electrical driver failure; a gradual one points back toward contamination and the stuck-off failure mode instead.
- 2.Check fluid level and condition, and look up whether this transmission's pressure control solenoids are normally high or normally low so the symptom can be interpreted correctly.
- 3.Fit a pressure gauge at the test port and record the pressure with the fault present.
- 4.Command the solenoid off with a scan tool and watch the gauge. Pressure that falls means the solenoid can still release and the fault is in the control side; pressure that does not move means the valve is stuck mechanically.
- 5.Disconnect the solenoid entirely and repeat the measurement. A solenoid that stays applied with no electrical connection at all is conclusively stuck, and no further electrical testing is needed.
- 6.If the solenoid does release when disconnected, check the control wire for a short to power and measure the module's output with the circuit connected. A driver stage holding the circuit on is a module-level repair rather than a transmission one.
- 7.Resistance-check the solenoid and inspect the connector for corrosion and fluid intrusion.
- 8.Drop the pan and inspect the fluid and magnet for the debris that most often causes a valve to wedge.
- 9.Once accessible, remove the solenoid and check the spool moves freely by hand in a clean bore. A spool that will not move is the answer; a spool that moves freely sends the search back to the control side.
Repair cost
$150 – $1,400
A fluid and filter service at $150 to $350 addresses the contamination that lodges debris in a valve, though it is a less reliable fix here than on the stuck-off code because a wedged valve does not always free itself. A solenoid replacement is $250 to $700 fitted. A valve body is $600 to $1,400. The scenario worth identifying early is the electrical one: if the fault is a shorted control wire or a failed module driver, the repair is a wiring or module job and no amount of transmission work will touch it — which is exactly why the command-off pressure test belongs at the start of the diagnosis rather than at the end.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with transmission shift solenoid replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.