P0758 - OBD Trouble Code

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Diagnostic trouble code P0758 is technically described as Shift Solenoid Electrical. This trouble code is associated with an electrical malfunction with the transmission Shift Solenoid "B" Circuit. If the PCM records code P0758, it indicates that the PCM cannot see the proper change in engine RPMs or the correct increase in road speed that should be happening during a shift from second to third gear.

The error code P0758 is detected when PCM is not seeing the specified rpm change that occurs during a shift from 2nd gear to 3rd gear. This is a generic transmission diagnostic trouble code (DTC) and typically applies to OBD-II vehicles equipped with an automatic transmission. The purpose of the automatic transmission is to match the engine's optimum power and torque characteristics to the driver's desired rate of acceleration and speed by auto-selecting different gear ratios or 'speeds' to power the wheels. Shift solenoid B enables the transmission to shift from 2nd gear to 3rd gear. 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 Electrical?

• Open or shorted shift solenoid circuit
• Faulty shift solenoid
• Faulty control module
• Low transmission fluid level
• Contaminated transmission fluid
• Faulty Wiring or connector
• Clogged transmission filter

1. Shift Solenoid - A shift solenoid is a required part of a functioning transmission, shift solenoids job is as it sounds, shifts the gears for you. A faulty shift solenoid can prevent fluid pressure from activating the appropriate gear. As a result, the transmission may not shift gears or it may get stuck in neutral. As this code is related to shift solenoid so make sure it should work efficiently else replace it immediately.
2. Shift Valves - Shift valves supply hydraulic pressure to the clutches and bands to engage each gear. The valve body of the transmission contains several shift valves. The shift valve determines when to shift from one gear to the next.
3. Transmission Filter - Clogged transmission filter restricts the flow of transmission fluid to go through from it. It should be replaced immediately if found clogged so that your vehicle can continue to drive at its optimal potential.
4. Transmission Valve Body - The transmission valve body is the top control area of the transmission. This valve body is responsible for directing hydraulic fluid (or transmission fluid) to various valves so the appropriate clutch can be activated. After this happens, you are able to shift the gear to whatever one you need for your particular driving situation. Repair or replace the faulty one in no time.
5. Powertrain Control Module - A powertrain control module, abbreviated PCM, is an automotive component, a control unit, used on motor vehicles. It is generally a combined control unit, consisting of the engine control unit (ECU) and the transmission control unit (TCU). Though it fails rarely but if in case it happens then do the necessary replacements immediately.

To identify any trouble code, one should be aware of the symptoms of that particular error code. Below are the common symptoms of error code P0758, which may help you to identify this error code:

• Fall in fuel efficiency
• Failure of the transmission to shift from any gear
• Transmission controller may enter into limp mode
• Other shift solenoid related codes may store as well
• Slippage of transmission
• Overheating of transmission
• Illuminated check engine light

As above mentioned, due to this error code you will start facing problem to shift from second to third gear which can result in a number of problems for an automatic transmission vehicle, and it can pose a hazard when driving as well. To ensure that you are safe and that your vehicle is able to run reliably, you should get this problem taken care of immediately. Following repairs or replacements may help you to overcome this error code:

• Check out the transmission fluid level, and top up if required.
• If transmission fluid is contaminated, change it immediately.
• Change the transmission fluid filter if required.
• Repair or replace a faulty shift solenoid and transmission valve body.
• Clean the blocked hydraulic blockages.
• Inspect the related wiring and connectors and replace the faulty one.
• Replace or flash the PCM.

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Here are some steps which you should follow in order to diagnose this P0758 fault code:

• 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.
• 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.

Common Mistakes When Diagnosing the P0758 Code

The most common mistake while diagnosing this error code is that usually people replace the shift solenoid without even inspecting that properly wherein the actual cause is something else. So, we always advise you to seek help of experienced diagnostician to do the needful.