Error Code P0759: What It Means & What To Do?

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P0759 OBD-II trouble code is associated with an intermittent fault in the transmission Shift Solenoid "B" Circuit. It means that the shift solenoid B may not be properly managing fluid levels between its hydraulic circuits. Although code setting parameters vary greatly from one manufacturer (and model) to another, virtually every application utilizes calculations based upon throttle position, engine load, engine speed, and vehicle speed to determine the desired gear ratio.

Error code P0759 is technically described as Shift Solenoid B Intermittent. P0759 code is detected when the gear required by the ECM does not match the actual gear when vehicle is driven. The automatic transmission relies on bands and clutches to change gears and this is accomplished by having fluid pressure in the right place at the right time. The transmission solenoids are responsible for opening or closing valves in the valve body to allow transmission fluid to flow to the clutches and bands to shift the transmission smoothly as the engine accelerates. If the desired gear ratio fails to coincide with the actual gear ratio detected, a code will be stored and a malfunction indicator lamp may be illuminated.

What causes this problem with the Shift Solenoid B Intermittent?

• Polluted transmission fluid
• Low level of transmission fluid
• Mechanical transmission failure
• Blocked transmission fluid passages
• Defective shift solenoid
• Poor electrical connections
• Failed PCM or control modules

1. Shift Solenoid - A shift solenoid is a computer controlled, electronically activated component of an automatic transmission system. There are multiple shift solenoids in a transmission. They are responsible to open/close certain valves in the transmission to regulate the flow of the transmission fluid, which causes the transmission to actually shift gears. Ensure its proper functioning and if you discover it faulty replace it.
2. Transmission Filter - As its name suggests it filters the transmission fluid and help prolong the life of your transmission by filtering out debris. Well-maintained or new filters keep contaminants out of your transmission fluid, averting premature transmission failure and ensuring a stress-free ride. . It should be replaced immediately if found clogged so that your vehicle can continue to drive at its optimal potential.
3. Transmission Valve Body - As the name suggests, automatic transmission valve body is a major component of a vehicle’s automatic transmission system. It works in a network form. The body directs pressurized transmission fluid to a network of valves that put together appropriate clutch packs for smooth gear functioning. If it is faulty then create drivability issues.
4. Powertrain Control Module - The Powertrain Control Module PCM is an on-board electronic control unit that primarily controls the charging, emission and transmission systems of the vehicle. It works in conjunction with a network of sensors, using their inputs to control the functioning of the engine and powertrain. Repair or replace the faulty components of PCM to ensure the smooth functioning of your vehicle.

Symptoms of this error code P0759 may vary from no detectable symptoms at all to a failure of the transmission to shift from (or into) any particular gear. Some common symptoms of this error code are as follows:

• Transmission Overheating
• Transmission Slippage
• Harsh Shifting
• Reduced fuel economy
• Inability to shift into gear
• Vehicle entering Limp mode.
• Illuminated check engine light

Error code P0759 is one of the serious error codes and should be rectified on priority. It affects your drivability as well due to inability of shifting gears. It should not be neglected else can lead to serious and costly transmission rebuild. To fix this error code following repairs or replacements may help:

• Changing the transmission fluid and filter
• Repair or replace a faulty shift solenoid
• Repair or replace defective transmission valve body
• Repair or replace defective transmission
• Cleaning corrosion from connectors
• Repairing or replacing wiring

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It is essential to diagnose this fault code. Here are some steps which a mechanic should follow for diagnosing the problem that triggered a P0759 code to be stored:

• Begin any transmission diagnosis with an inspection of the transmission fluid dipstick (if equipped).
• Make sure that the fluid level is within manufacturer’s specified recommendations and that the fluid is in good condition.
• Visually inspect all internal wiring and connectors, look for shorted or burned wiring and replace circuitry and connectors as required.
• If the system wiring, connectors, and components appear to be in normal working order, connect the scanner to the diagnostic connector and record all stored trouble codes and freeze frame data.
• If the transmission fluid appears to be in decent shape, but the fluid level is low, add enough fluid to locate a leak and repair it.
• If either the reference voltage or ground circuits are open, use the digital volt/ohmmeter to check for continuity (disconnect all related control modules from the circuit before checking circuit resistance or controller damage may occur) and resistance in all circuits.
• Repair or replace system circuitry, connectors, and/or components that fail to coincide with manufacturer’s specs.
• Always retest the system to ensure a successful repair. If all system circuits are intact connect the scanner to the diagnostic connector and attempt to manually activate the shift solenoid/s in question.
• If the shift solenoid functions properly and all circuits coincide with manufacturer’s specifications, suspect a defective PCM.
• Remember that PCM failure is rare and replacement will require reprogramming.

Common Mistakes When Diagnosing the P0759 Code

Most commonly, mechanics will replace shift solenoid B without conducting a full diagnosis. While a failed solenoid is often the culprit, there are other factors that must be ruled out. Often, low transmission fluid is the problem.