|Code||Fault Location||Probable Cause|
|P0755|| Shift solenoid (SS) B -circuit malfunction |
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|Wiring, shift solenoid, ECM/PCM!TCM|
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What Does Code P0755 Mean?
OBD II fault code P0755 is a generic code that is defined as “Shift solenoid (SS) B -circuit malfunction”, and is set when the PCM (Powertrain Control Module) or TCM (Transmission Control Module) detects an electrical malfunction either in the transmission shift solenoid labelled “B” itself, or in the “B” solenoid’s control circuit.
All automatic transmissions use computer controlled solenoids to shift pressurized transmission fluid between hydraulic circuits to accomplish gear shifts. Regardless of the number of gear ratios any given transmission has, each gear shift is accomplished by a shift solenoid that is dedicated to one gear ratio. 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 practical terms, when a gear shift is initiated, the solenoid that controls the next higher or lower gear is energized by the PCM/TCM. This action redirects pressurized fluid into the hydraulic circuit(s) that controls the selected gear ratio. Thus, when a particular hydraulic circuit is pressurized, all the transmission components that select and maintain that gear are moved into position in a series of events that is roughly analogous to the way different combinations of gears are selected to establish different gear ratios in manual transmissions.
Therefore, when the PCM/TCM detects a malfunction in the control circuit of shift solenoid “B”, the controller can no longer control gear shifts efficiently, and code P0755 will be set and a warning light may be illuminated as a result.
The image below shows the typical arrangement of transmission shift solenoids. In many cases, shift solenoids are not accessible from outside of the transmission, which means that the transmission oil pan has to be removed to access individual shift solenoids, internal wiring, or to a shift solenoid pack that can only be replaced as a complete unit. Note that the arrangement of shift solenoids varies greatly between manufacturers; refer to the manual for the affected application to determine the exact location of shift solenoid “B” relative to other components.
What are the common causes of code P0755 ?
Some common causes of code P0755 could include the following-
- Defective shift solenoid
- Mechanical failure of the transmission
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Low transmission fluid level
- Dirty, contaminated, or degraded transmission fluid
- Use of unsuitable or incompatible transmission fluid
- 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 P0755 ?
Some common symptoms of code P0755 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 P0755 ?
NOTE #1: Non-professional mechanics are limited to only a few basic checks and tests when diagnosing this code. Also note that advanced diagnostic/repair steps are almost invariably make and model specific, and performing these steps generally requires professional grade diagnostic equipment, above average diagnostic skills, and expert level knowledge of the affected application.
NOTE #2: The few generic diagnostic/repair steps outlined below are intended to be for general informational purposes only, and may or may not resolve code P0755. If these steps outlined hare do not resolve code P0755, the better option is to refer the vehicle to the dealer or other competent repair facility for professional assistance.
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. Also note that degraded fluid or a low fluid level are unlikely to cause electrical issues, unless the degraded fluid or low fluid level has caused mechanical damage that in can turn conceivably cause electrical short circuits.
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. 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 “B” in the transmission side of the connector, and perform resistance and continuity checks on these wires as per the instructions in the manual.
Make repairs or replace damaged wiring 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” fluid fill. Draining and refilling these transmissions almost always requires equipment that is generally not available to the average non-professional mechanic.