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... What is a Transmission Solenoid?
... What Exactly Do Transmission Solenoids Do?

... Symptoms of a Failed Solenoid
... Solenoid Replacement and Cost
... Save Money on Any Transmission Solenoid

We'll cover all these topics and more below.

What is a Transmission Solenoid?

A transmission solenoid is an electro-mechanical component "valve" used to control the flow of transmission fluid in the transmission.  A typical automatic transmission uses a number of different solenoids for different purposes.  The opening and closing of the solenoids is controlled electronically by the vehicle's Engine Control Module (ECM) or Transmission Control Module (TCM), depending on the vehicle.

A modern-day transmission uses solenoids to engage and shift gears, called shift solenoids

, which are normally mounted to the transmission valve body.  There is also a Transmission Pressure Control Solenoid and a Torque Converter Clutch Solenoid.

What Exactly Do Transmission Solenoids Do?

The best way to explain what transmission solenoids do is to describe the different solenoids that are used in an automatic transmission.  The following describes the different solenoids along with their functions.  Also included are problem symptoms, repair information, parts and estimated repair costs.

Shift Solenoid: DESCRIPTION
As the name suggests, shift solenoids are used to control gear engagement and gear shifts. It works something like this... When the Engine Control Module (ECM) or Transmission Control Module (TCM) determines it is time to shift to a different gear, (or when the driver manually shifts the transmission), electrical pulses cause the appropriate shift solenoid valve to open. The opening of the solenoid allows transmission fluid to flow to the bands and clutches to effect the desired gear shift. The fluid provides the pressure needed to apply the bands and clutches to engage the gear.

Symptoms of a Faulty Shift Solenoid
There primary problem symptoms of a faulty shift solenoid are delayed shifts, no downshifts and erratic shifts. 
Delayed Shifts:
When the shift solenoids are working properly, shifts occur smoothly and without delay.  A faulty shift solenoid can cause delayed shifts of a few seconds or up to one minute or longer.  During a shift delay no power is delivered to the drive wheels - it's as if the shifter is in neutral.  These shift delays can occur when you first shift the transmission into a gear and when the transmission is shifting between gears.

No Downshift(s): When the shift solenoids are function properly, the transmission automatically downshifts as the vehicle speed slows.  When the vehicle comes to a complete stop the transmission downshifts into first gear.  A faulty shift solenoid can cause the transmission to downshift uncontrollably (in other words at random times) or not downshift at all, even when coming to a complete stop.

Erratic Shifts: A defective shift solenoid can also cause the transmission to shift erratically.  This can be described as shifting into the wrong gear, skipping the intended gear and shifting back and forth between two gears.


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Once it is determined that you have a failed transmission shift solenoid the only repair is to replace the faulty part.  Replacing a transmission shift solenoid can be done by most any auto repair shop, automobile dealership service center or you can do-it-yourself "DIY".

Replacing a transmission shift solenoid or a shift solenoid pack involves dropping the transmission oil pan in order to access the valve body, (where the solenoids/solenoid pack is mounted), locating and replacing the faulty solenoid and then replacing the oil pan using a new pan gasket before refilling the transmission with the correct automatic transmission fluid (ATF).

NOTE: On some vehicles, the transmission solenoids are part of a solenoid pack.  In these instances, you must replace the solenoid pack.

My Automatic TransmissionShift Solenoid: REPLACEMENT COST 
The cost for transmission solenoid replacement depends heavily on the type of vehicle you drive.  For example, a single transmission shift solenoid can cost anywhere from $15 to $100.  A solenoid pack, which includes all the solenoids for a particular vehicle/transmission can cost from $65 to several hundred dollars or more.  Where you get the work done, (whether at a local auto repair shop, car dealership or you do-it-yourself), also factors heavily into the cost of repair.  If you replace the solenoid yourself, the parts supplier you purchase the solenoid (or solenoid pack) from will factor into your final cost.

Below are transmission solenoid replacement costs for four different vehicles.  Use this information to give you a rough idea of what your cost might be.

 Transmission Shift Solenoid Replacement Cost
REPAIR: Replace shift solenoid
DIY COST: $40 to $65
DIY SAVINGS: $195 to $295
REPAIR: Replace failed solenoid pack
DIY COST: $140 to $160
DIY SAVINGS: $150 to $275 

  VEHICLE: 2008 BMW 330i
REPAIR: Replace solenoid pack
DIY COST: $245 to $265
DIY SAVINGS: $390 to $485 
REPAIR: Replace shift solenoid
DIY COST: $35 to $45
DIY SAVINGS: $140 to $190  
Normally the transmission fluid that is drained from the pan when replacing a solenoid or solenoid pack is reused.  If you choose to replace this fluid with new fluid the approximate cost is $20 to $50.  ATF costs between $6 and $10 per quart and you will need 3 to 5 quarts.  


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Diagnosing a failed transmission solenoid with Check Engine Light
A failed transmission solenoid will normally set a diagnostic trouble code (DTC), which will cause the check engine light to illuminate.  In these instances, an OBD-II scan of your vehicle's computer will provide information pointing to the faulty solenoid.  The DTC information (or explanation) will almost always include a statement indicating that the problem may be an open circuit in the transmission electrical system.  Therefore, you should always test the solenoid to verify its condition before replacing it.

Diagnosing any Transmission Problem with NO Check Engine Light
A correct diagnoses of a transmission problem when there is no check engine light is best accomplished with a professional transmission scan.  This type of scan will necessitate a visit to a transmission shop or car dealership.  A professional transmission scan can cost between $60 and $125.  This charge is normally referred to as a diagnostics fee.  It is standard procedure for the shop making the repair to waive the diagnostics fee.

Fail Safe (or Limp Mode)
A failed transmission solenoid or an open circuit anywhere in the electrical system may cause the transmission to go into Fail Safe (or "limp" mode as it is also called) in order to protect the transmission from internal damage that might be caused by the faulty solenoid or open circuit.  In fail safe/limp mode, the transmission will have limited functionality and will lock in either 2nd. or 3rd. gear.  When the transmission is in fail safe mode, the vehicle should only be drive home or to the repair shop.  Maximum speed while in limp mode is around 30 mph.

Continuing to drive the vehicle with the transmission in fail safe or driving faster than the recommended fail safe speed will cause the transmission to overheat.  Excessive heat build up in an automatic transmission is the #1 cause of catastrophic failure.  So, avoid extended driving when the transmission is in fail safe mode.

Transmission Tip A transmission that goes into limp mode will sometimes reset itself when the engine is shut off and restarted.  So, if you find yourself in this predicament, find a safe place to pull off the road and shut the engine off, wait a minute or so and then restart it. 
Next...  Transmission Pressure Control Solenoid  
Transmission Torque Converter Clutch Solenoid  

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