Paranoid about a Faulty Solenoid: Troubleshooting for Automatic Transmissions

Posted by on Tuesday, January 22nd, 2013

Shift solenoids became popular in automatic equipped cars in the early 1990’s. In older transmissions the valves inside the valve body are all hydraulically moved by some type of mechanical device that releases fluid into certain parts of the valve body. In a move to gain more control over the shifting quality and timing of the transmission, auto makers started using electrical solenoids to dictate how the transmission behaved. The solenoids were energized by a relay that received an electric signal from the computer. The use of solenoids ushered in a new period of electronically controlled transmissions.

typical automatic transmission solenoid


Most shop owners have seen their fair share of customers bringing in cars with late model automatic transmissions that have one problem or another. Often the solenoids are responsible for these problems. This is especially true of the earlier transmissions that used this technology. Solenoid failure was high mainly because this technology was new and knowledge about building a durable solenoid was still unfolding or not yet discovered.


typical layout of a transmission solenoid



Shift solenoids are nothing more than a fancy electrical magnet. Inside the solenoid is a plunger that moves back and forth. A spring is used to keep the plunger in one position when the unit is at rest, or in other words in not energized. Surrounding one end of the plunger is a magnet made up of hundreds of turns of fine, coated wire. When voltage is applied to the coil of wires a magnetic field forms. The magnetic field draws the metal plunger towards it and at the same time collapses the spring holding the plunger. When the voltage entering the solenoid is discontinued, the magnet field disappears and the magnet releases its hold on the plunger. The spring inside the solenoid then pushes or pulls the plunger back to its resting place. The plunger is usually connected to a valve in the valve body and this valve moves back and forth when the solenoid is activated, allowing pressurized hydraulic fluid to move from one chamber to another.





There are a couple ways to check for a faulty solenoid. The first one involves using an Ohm meter to check the resistance inside the coil of wires located in the solenoid. A working solenoid will have a resistance of somewhere between 20 and 30 ohms. This number can vary from manufacturer to manufacturer so be sure to refer to the repair manual for proper readings. If the wire inside the solenoid is broken it will have no resistance at all. If the wire is not broken but the coating around each individual wire has worn away or melted away, the resistance will be lower because the path of electricity will be shorter due to two or more wires having touched each other and bypassed a distance of the wiring (they have shorted out.) The other way to check is to use a hand held controller to see if the vehicles computer is putting out any error codes.

Hopefully this information will help assist you in your repairs! If your transmission problems aren’t the result of a faulty solenoid and you’re looking at larger, more costly problems, you may want to consider a remanufactured unit!

re-manufactured transmission will include major alterations and upgrades designed to make them both stronger and more durable. A re-manufactured transmission will also include a much better warranty; three years compared to an average 90 days for a rebuilt transmission. As a bonus, in the rare event that a re-manufactured transmission fails within the warranty period, they will cover your R&R cost to replace your customer’s transmission. And remember, the companies that re-manufacture transmissions are very easy contact. They are just a quick phone call or email away from helping you out.

4 Responses to “Paranoid about a Faulty Solenoid: Troubleshooting for Automatic Transmissions”

  1. [...] this is an electronic transmission it contains a number of solenoids. All of them are subject to failure. The two to keep an eye on are the transmission pressure control solenoid and the torque convert [...]

  2. [...] converter. There is an easy and inexpensive way to check your solenoids to see if they are bad. Get out your ohm meter and check the resistance of the solenoid. Hook the black and red wires from your ohm meter to the two leads coming off the solenoid.  If [...]

  3. [...] This transmission is loaded with electrical components. It incorporates multiple electrical solenoids and sensors, not to mention a fairly complex wire harness. All electrical transmissions suffer from similar [...]

  4. [...] just like every other electronically controlled transmission. The biggest issue electronically is all the electrical solenoids this transmission incorporates. They control all the forward gears and the torque converter clutch. If you suspect that a solenoid [...]

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