|Code||Fault Location||Probable Cause|
|P0751|| Shift solenoid (SS) A -performance or stuck off |
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|Wiring, shift solenoid|
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What Does Code P0751 Mean?
OBD II fault code P0751 is a generic code that is defined as “Shift solenoid (SS) “A” -performance or stuck off”, and is set when the PCM (Powertrain Control Module) or TCM (Transmission Control Module) detects an abnormal signal voltage, or a voltage that indicates that the transmission shift solenoid labelled “A” is stuck in the “OFF” or closed position.
All automatic transmissions use electrically operated, and computer controlled solenoids to shift pressurized transmission fluid between hydraulic circuits to affect gear shifts, and regardless of the number of gear ratios any given transmission has, each gear is selected/deselected by a dedicated shift solenoid. For instance, while some older transmissions may have only four shift solenoids labelled “A”, “B”, “C”, and “D”, newer transmissions usually have more ratios, with the additional shift solenoids labelled “F”, “G”, and “H”, for a total of seven shift solenoids.
In terms of operation, when a gear shift is initiated the solenoid that controls the next higher (or lower) gear is energized by the PCM/TCM, which redirects pressurized fluid into the hydraulic circuit(s) that controls that particular gear ratio. Thus, when a particular hydraulic circuit is pressurized, all the transmission components that select that gear are moved into position. The pressurized fluid then maintains pressure on clutch packs, which in turn, prevents the rearranged planetary gears from disengaging. This series of events is roughly analogous to the way different combinations of gears are selected to establish different gear ratios in manual transmissions.
When the PCM/TCM detects a problem with shift solenoid “A”, the controller can no longer control gear shifts efficiently, and it will set code P0751, and illuminate a warning light as a result.
The image below shows how shift solenoids are typically arranged. Note though that shift solenoids are often not accessible from outside of the transmission, and in these cases, the transmission oil pan must be removed to gain access to individual shift solenoids, internal wiring, or sometimes to a shift solenoid pack that must be replaced as a complete unit. Note that the arrangement of shift solenoids in this image is for illustrative purposes only; refer to the manual for the affected application to determine the exact location of shift solenoid “A”.
What are the common causes of code P0751 ?
Some common causes of code P0751 could include the following-
- Low transmission fluid level
- Dirty, contaminated, or degraded transmission fluid
- Use of unsuitable or incompatible transmission fluid
- Clogged hydraulic passages in the transmission or valve body
- Defective shift solenoid
- Mechanical failure of the transmission
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Failed or failing PCM/TCM. Note that this is a relatively rare event, and the fault must be sought elsewhere before any controller is replaced
What are the symptoms of code P0751 ?
Some common symptoms of code P0751 could include the following-
- Stored trouble code and an illuminated warning light
- Other transmission related codes may be present as well
- Varying degrees of transmission slippage may be present
- Transmission may be stuck in a particular gear
- Transmission may not engage the affected gear
- Fuel consumption may increase
- Transmission may overheat
- Transmission may enter a fail-safe or limp mode
- In some cases, the engine may exhibit symptoms that resemble those of misfires on one or more (or all) cylinders.
How do you troubleshoot code P0751 ?
NOTE #1: Non-professional mechanics are limited to basic checks and tests when diagnosing this code. Also note that advanced diagnostic/repair steps are make and model specific, and performing these steps generally requires special equipment, above average diagnostic skills, and expert level knowledge of the affected application.
NOTE #2: The few generic diagnostic/repair steps outlined below are for general informational purposes only, and may or may not resolve code P0751. If these steps do not resolve the problem, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair.
Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.
If the application is fitted with a dipstick, check the fluid level as per the instructions in the manual, and adjust the level as required. Also check the condition of the fluid; if it is dark in color, has a burnt smell, or has a thick, tarry consistency, the fluid is degraded and it must be replaced.
NOTE: If the transmission has a “life-time” fill, refer the vehicle to the dealer or other repair facility that has the equipment to drain and refill the transmission to the correct level.
If the fluid is up to the proper mark and in good condition, locate the transmission wiring harness, and inspect it for damage or corrosion. Also perform a thorough visual inspection of all related wiring- look for damaged, burnt, shorted, disconnected, or corroded wiring. Repair or replace wiring or the connector as required.
If the connector is in good condition, refer to the manual to determine the function and color coding of each wire in the connector. Identify the wires that relate to shift solenoid “A” in the transmission side of the connector, and perform resistance and continuity checks on these wires as per the instructions in the manual.
Unless the manual says otherwise, the resistance reading for shift solenoid “A” should be zero. If there is a resistance, the circuit is short circuited. If there is no continuity in the circuit, the circuit is open. Make repairs as required, and retest the system to verify that all electrical values fall within the ranges specified by the manufacturer.
NOTE: If faults and discrepancies are found in the transmission’s internal wiring, the entire internal harness must be replaced as a complete unit to avoid issues with short circuits caused by metal wear particles in the transmission fluid.
If the generic steps up this point did not resolve the problem, refer the vehicle to a competent repair facility for professional assistance, and especially if the transmission has a “life-time” fill, since draining and refilling these transmissions require equipment that is generally not available to the average non-professional mechanic.