P0798Generic code

P0798 Code: Pressure Control Solenoid C Electrical

The P0798 code means the transmission control module found an electrical fault in pressure control solenoid C: an open circuit, a short or a resistance out of range. Check the transmission connector and wiring before you replace the solenoid. The transmission can shift harshly or drop into limp mode.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$80 to $900
Difficulty
Medium
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0798 code means

Solenoids are electric valves that direct fluid pressure to the clutches and bands inside the transmission. Pressure control solenoid C regulates the pressure of another group of clutches in transmissions with many speeds. The transmission control module commands these solenoids and watches both their electrical circuit and the result, meaning the input and output shaft speeds.

The P0798 code points to an electrical fault in the solenoid: an open circuit, a short or a resistance out of range. The suspects are the wiring, the connector (very often the pass-through connector on the case, which leaks fluid), the solenoid itself or the control module.

On any transmission code, the first check is the fluid: correct level using the manufacturer procedure (often with the engine running and at a specific temperature), a red or pink color and no burnt smell. Low or degraded fluid causes slipping, harsh shifts and solenoid or gear ratio codes that disappear once it is corrected.

Always start with the simplest items: fuse, relay and connector. Then check power, ground and signal with the component connected (using back-probes), and finally the continuity of each wire up to the computer. Only if all of that is good should you replace the component.

See the P0700 guide to understand how transmission codes are read and why you need a scan tool that can talk to the transmission module.

P0798 code symptoms

  • Check engine light or transmission warning light on.
  • Shifts that are harsh, late or that do not happen at all.
  • Limp mode: the transmission stays in one fixed gear (often 2nd, 3rd or 4th).
  • Slipping or high rpm in certain gears.

Likely causes of the P0798 code

  1. Transmission connector with fluid inside or corrosion. Very common at the pass-through connector on the case.
  2. Internal or external wiring damaged by heat or rubbing.
  3. Solenoid with an open or shorted coil, with a resistance outside the specification.
  4. Transmission control module. Uncommon.

How to diagnose the P0798 code step by step

  1. Check the fluid level and condition using the manufacturer procedure.
  2. Read all the codes in the transmission module with a scan tool that can access it.
  3. Measure the solenoid resistance at the transmission connector and compare it with the manual.
  4. Check the insulation to ground. It should read infinite.
  5. Command the solenoid with the scan tool and listen for the click.
  6. Inspect the case connector for fluid inside it or green pins.

How to fix the P0798 code

  • Repair the connector or the wiring.
  • Replace the solenoid (or the valve body, if the solenoid comes built in).
  • Clear the adaptations and run the relearn procedure.
  • Clear the codes and verify the repair on a road test.

Technical reference data

  • Shift solenoids (on/off): roughly 10 to 30 ohms.
  • Pressure or linear solenoids (PWM control): roughly 3 to 8 ohms.
  • Normal transmission fluid temperature: 70 to 95 °C (158 to 203 °F).
  • These are approximate values: check the manufacturer data for your vehicle.

Brand-specific notes

On many transmissions the solenoids sit in the valve body, and you reach them by removing the pan. Some solenoids are sold only together with the valve body or with the integrated control module. After replacing solenoids or the valve body, you usually need to clear the adaptations and run a relearn with a scan tool.

P0798 on Aisin, Jatco, GM 6T and Ford 6R Transmissions

On these units the solenoids are in the valve body, and you get to them by dropping the pan.

P0798 on Volkswagen DSG

On the Volkswagen DSG and on many modern transmissions, the solenoids come built into the mechatronic unit (the valve body with its control module), so they are often not sold separately.

Frequently asked questions about P0798

What does the P0798 code mean?
It is a generic OBD2 code that means the control module found an electrical fault in pressure control solenoid C. That can be an open circuit, a short or a resistance outside the specification.
Can I drive with a P0798 code?
With caution, and only as far as a shop. A transmission with the P0798 code can drop into limp mode, and driving like that for a long time wears it out.
Will a fluid change fix it?
Sometimes it helps on performance or stuck codes. On an electrical fault like this one, it will not.
Does the transmission have to come out?
Normally not. The solenoids are replaced by removing the pan or the valve body cover.
How much does it cost to fix P0798?
As a rough guide, between $80 and $900. It costs more if the transmission itself has to be repaired.
Will a P0798 code clear itself?
If the connection was only loose or damp, the light can go out for a while. A real open or short in the solenoid or the wiring will bring the code back.
What is the most common cause of P0798?
A damaged connector or wiring, most often the pass-through connector on the transmission case filling with fluid or corroding. Check it before you buy a solenoid.

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