P0798

Pressure Control Solenoid C Electrical

P0798 is a generic OBD-II powertrain diagnostic trouble code: Pressure Control Solenoid C Electrical. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0798
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P0798 means

P0798 is a generic automatic-transmission code set by the transmission control module (TCM) or powertrain control module (PCM) when it detects an electrical fault in the circuit for pressure control solenoid "C". Pressure control solenoids are current-controlled valves in the valve body. The module varies the current through each one to position a regulator valve, which in turn sets the hydraulic pressure fed to a specific clutch or band, or to the main line pressure circuit. Getting that pressure right is what makes a shift feel smooth.

The letter "C" simply identifies the third pressure control solenoid in the manufacturer's numbering scheme, so which physical valve it refers to depends entirely on the transmission. You need the correct wiring diagram and valve-body layout for the vehicle in front of you before probing anything. The code is stored on electrical evidence only: the module commands a current and then measures the circuit's response. An open circuit, a short to ground, a short to battery voltage, or a resistance well outside the expected window all trigger P0798.

It helps to separate P0798 from its neighbours. P0796 means solenoid "C" is not performing or is stuck off and P0797 means it is stuck on, both of which are hydraulic or mechanical faults. P0798 points at the electrical path, so the solenoid winding, the internal transmission harness, the case connector and the module driver are where diagnosis should begin. Once the code sets, the module normally reverts to a fixed-pressure failsafe strategy.

Common causes

Most-frequently reported root causes when P0798 is logged.

  • 1
    Failed pressure control solenoid "C" with an open, shorted or out-of-specification coil.
  • 2
    Damaged internal transmission harness wiring rubbing on the case or valve body.
  • 3
    Corroded or oil-contaminated transmission case connector with poor terminal contact.
  • 4
    Low or badly degraded transmission fluid, which overheats solenoids and shortens their life.
  • 5
    Contamination or varnish holding the solenoid spool, producing abnormal current draw.
  • 6
    Chafed or rodent-damaged external harness between the transmission and the control module.
  • 7
    A failed solenoid output driver inside the TCM or PCM.
  • 8
    Weak module power or ground supply, or a low battery, causing false electrical diagnostics.

Symptoms drivers notice

Check engine light on, often with a transmission fault message on the dash.
Shifts feel stiff and abrupt, or take several seconds to complete.
Slipping or flaring between gears, especially under acceleration.
The transmission enters limp mode and stays in one gear.
Noticeably worse fuel consumption and higher engine speed at cruise.
In some cases the car will not shift out of park or reverse behaves oddly.

How to diagnose P0798

A typical diagnostic flow when this code is present.

  1. 1
    Scan all modules, record freeze-frame data and note any companion solenoid or line pressure codes that hint at a shared power feed or ground.
  2. 2
    Confirm the transmission fluid level and inspect its colour and smell, since burnt fluid or metal glitter means internal damage that must be addressed first.
  3. 3
    Look up the wiring diagram for that specific transmission to identify which physical solenoid the letter "C" refers to and where its pins land in the case connector.
  4. 4
    Inspect the case connector and accessible harness for corrosion, fluid seepage into the connector body, chafing and loose or backed-out terminals.
  5. 5
    Monitor commanded versus actual solenoid current in live data while driving or during a bi-directional actuator test, and note whether the fault comes and goes with temperature.
  6. 6
    With the control module unplugged so its drivers are protected, measure solenoid resistance and check the circuit for shorts to ground and to battery voltage, wiggle-testing the harness as you go.
  7. 7
    Only if the solenoid and harness both meet specification, verify module power and grounds at the module connector before considering a TCM or PCM fault.

Related powertrain codes

Frequently asked questions

Can I keep driving with P0798?

Keep it to short, low-speed trips to a workshop. Incorrect clutch pressure makes clutches slip, and slipping clutches burn. Continuing to drive can turn a solenoid or wiring job into a transmission rebuild.

Will P0798 fail an emissions test?

Yes. It is a stored powertrain fault with the MIL illuminated, and an OBD-II inspection fails any vehicle with the check engine light on, whatever the code refers to.

Is this expensive to fix?

It depends on what is actually broken. A connector clean-up or wiring repair is inexpensive. Replacing the solenoid or the internal harness needs the pan or valve body off, which adds several hours of labour plus fluid and a filter.

Why did my transmission suddenly lock into one gear?

That is the module's failsafe response. Once it cannot trust its pressure control it stops trying to shift normally and holds a safe gear at a fixed pressure to protect the clutches until the fault is repaired.

Disabling P0798 in software

RaceTune can permanently disable P0798 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECU families we can disable P0798 on

We hold the DaVinci A2L disable definitions for these families, so the exact P0798 path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.

  • Bosch EDC17C66 verified
  • Bosch EDC17CP57 verified

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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