P0796 – Transmission fluid pressure (TFP) solenoid C performance or stuck off

By Reinier (Contact Me)
Last Updated 2020-08-11
Automobile Repair Shop Owner

What Does Code P0796 Mean?

OBD II fault code P0796 is a generic trouble code that is defined as “Pressure Control Solenoid “C” Performance/Stuck Off”, and is set when the PCM (Powertrain Control Module) detects a fault, failure, or malfunction that prevents the (automatic) transmission fluid pressure control solenoid labeled “C” from being cycled from the “OFF” position to the “ON” position.

Note that some advanced transmission designs may use multiple pressure control solenoids for different functions and/or purposes, and in these cases, pressure control solenoids are typically labeled “A”, “B”, “C”, “D”, and so on. Therefore, the exact function of the pressure control solenoid labeled “C” on any affected application must be determined from reliable service information.

NOTE: Pressure control solenoids should not be confused with shift solenoids. The former performs overall pressure control functions in the larger transmission, while the role of shift solenoids is limited to switching already pressurized fluid between hydraulic circuits in the valve body to enable shifts between gears.

All automatic transmissions use pressurized fluid to perform functions such as engaging/disengaging clutch packs, engaging/disengaging the torque converter lockup clutch, or to alter the arrangement of planetary gear sets to effect gear shifts.

As a practical matter, the transmission fluid is pressurized by an engine-driven pump, and the flow/direction of the pressurized fluid is controlled by one or more pressure control solenoids, which are in their turn, controlled/managed/monitored by the transmission control module. In general terms, fluid pressure control solenoids are therefore used to ensure that sufficient pressure is always available at all points in the transmission to ensure that gear shifts are performed not only smoothly and reliably, but also at predetermined shift points.

Thus, given that the efficient circulation of pressurized fluid is essential for the transmission to work efficiently and reliably, it is critically important that all pressure control solenoids work as intended. Therefore, if the PCM detects any failure, malfunction, or defect that affects the operation of the pressure solenoid labeled “C”, it will recognize that it cannot control/manage the transmission effectively, and it will set code P0796 and illuminate a warning light as a result.

It should be noted though that depending on the application and the specific function of pressure control solenoid “C”, the PCM might also initiate a fail-safe or limp mode to limit engine power as a means of protecting the transmission against damage.

Where is the P0796 sensor located?

The image above shows an example of a typical transmission pressure control solenoid. Note though that since these solenoids are typically located at various points inside a transmission, they are generally not accessible without at least partial disassembly of the transmission. Therefore, it is recommended that professional assistance with diagnosis and repair be sought when code P0796 is present on any vehicle.

What are the common causes of code P0796 ?

Typical causes of code P0796 are largely similar across all applications, and could include one or more of the following-

• Dirty, contaminated, or degraded transmission fluid
• Dirty or clogged transmission filter
• Defective or faulty transmission pressure pump
• Mechanical failure of one or more transmission components other than the pressure pump
• Defects in the transmission valve body that effectively block or plug one or more hydraulic circuits; a typical example is a failed shift solenoid that restricts the flow of fluid around the transmission
• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connecter both inside and outside the transmission
• Failed or corrupted control module software
• Failed or failing PCM or TCM (Transmission Control Module), but since this is a rare event, the fault must be sought elsewhere before any control module is replaced or reprogrammed

What are the symptoms of code P0796 ?

Typical symptoms of code P0796 vary somewhat between applications but note that symptoms are largely dependent on the application, the role/function of pressure control solenoid “C”, and the exact nature of the problem. Nevertheless, typical symptoms could include one or more of the following-

• Stored trouble code and illuminated MIL (CHECK ENGINE) light
• Note that multiple other transmission-related codes may be present along with P0796
• Transmission may overheat
• Transmission may exhibit varying degrees of slippage
• Mechanical noises may or may not be present, but not that the absence of mechanical noises should not be taken as lack of evidence of mechanical damage to the transmission
• Transmission may be stuck in one gear
• Transmission may not be able to select any gear or only some gears
• Gear shifts may be harsh, erratic, or unpredictable
• Engine may stall at low speeds
• Engine may run roughly in a way that is reminiscent of random misfires
• If the vehicle is still drivable, fuel consumption may increase over extended periods if the fault is not corrected
• Depending on both the application and the exact nature of the problem, the vehicle may be in a fail-safe or limp mode that may persist until the fault is found and corrected

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