The shift solenoid controls the flow of the transmission fluid – it decides when to transfer this fluid and what rate it’s transferred at. Automatic transmissions nowadays use pressurize hydraulic fluid to change the gear – this allows the gear to change automatically without you having to do it yourself. When a gear change is needed, the TCM sends an electrical signal telling the shift solenoid to transfer transmission fluid into the valve of the body to engage the gear that’s needed.
If the solenoid fails to transfer transmission fluid into the valve of the body, or one of the mechanical valves fail, this can cause transmission issues. Luckily, there are a lot of common problems associated with it so you should be able to notice it.
What is a Shift Solenoid?
The shift solenoid changes the gear automatically in automatic vehicles by transferring transmission fluid into the valve of the body to engage the correct gear needed. While you’re driving, the vehicle’s computer uses the vehicle’s speed sensor and the engine speed sensor and analyzes it. Depending on the information it received, the Engine Control Unit will perform the correct transmission shift by sending a signal to the shift solenoid – depending on how fast you’re going and the RPM the engine is running at, the shift will either be downwards or upwards.
Each solenoid has a spring beneath it, and this is wrapped around with an electrical wire. When the wire receives a signal from the Engine Control Unit or the Traction Control Unit, it causes the spring to fling open and this allows transmission fluid into the valve body. The transmission fluid then selects the gear needed by pressurizing it – this causes the gear to change as you’re driving. The Engine Control Module controls the engine by opening or closing the hydraulic circuit using a signal. It can turn the ground circuit on and off. Depending on the design of the vehicle’s gears, it can control a single gear or multiple gears.
Since the Engine Control Unit or Traction Control Unit sends a signal to the spring loaded plunger, also known as the transmission control unit – if it’s not able to open, this will store an error code in the transmission control unit and this will confirm that the shift solenoid is damaged. There are also multiple problems that can happen to the shift solenoid that will cause it to fail.
Symptoms of Bad Shift Solenoid
If you have a shift solenoid and you want to know if it’s bad, there are a few ways that you can tell. You’ll notice a few gear related symptoms that’ll help you diagnose the problem. If you find that your vehicle is experiencing any of these problems, you need to head down to the mechanic as soon as possible – not being able to change transmission smoothly can mess up the rest of the vehicle.
Check Engine Light – the best way to know for sure without having to check any symptoms is by looking at the dashboard – if you see that the check engine light is on, this can be a big indicator that there’s something wrong with the shift solenoid so you’ll have to check with an OBD2 scanner. When there’s a problem in the vehicle, a trouble code is sent to the related unit and this can be diagnosed with an OBD2 scanner.
If you want to find out what this error code is, then you can use an OBD2 scanner. An OBD2 scanner is a diagnostic system that sometimes comes with your vehicle and it’s used to check the engine and other vehicle systems. It also communicates all the possible glitches that happen to them. You can use an OBD2 scanner (View on Amazon) to check what the error codes mean within your car.
If the check engine light comes on, you can connect the OBD2 scanner to the OBD connector that is under the steering portion of most vehicles. Once this is done, you can switch on your car’s ignition and turn all the other devices connected into the car. Once the computer and car are connected, press the red button on the scanner so it can check everything going on in the engine control unit.
After the scan is complete, a professional OBD2 scanner will allow you to find out what the error codes mean whereas a standard one will force you to write down the error codes and look them up somewhere else. From here, you can find out whether the error code was related to a bad shift solenoid or not. If the problem was a bad shift solenoid, you’ll need to take it to the mechanic to get it checked out.
Shifting Delays – If you’re traveling down the road and you notice that the transmission isn’t shifting like normal, this can indicate that the shift solenoid is bad. The shift solenoid needs to send transmission fluid to pressurize the correct gear – the Engine Control Unit or the Traction Control Unit is meant to send an electrical signal to the shift solenoid and if it can respond at a correct time, this will indicate that the shift solenoid is bad. In this case, you’ll need to head down to the mechanic to get the shift solenoid replaced.
Gears Skipping – when the gear change is needed, it can either shift up or down. For it to shift up, it must climb up all the gears just to reach the desired one – this is the same for when the gear needs to go down, it’ll go through each gear until it’s met it’s desired one. If you notice that the transmissions are skipping gears, this can indicate that there’s low transmission fluid. Transmission fluid is needed to lubricate the components of the car’s transmission for optimal performance – if the components aren’t lubricated properly, it can cause the gears to skip. To check if this is the case, you can check the transmission fluid level.
Stuck in Gears – if you notice that the gears are stuck, this will indicate that the shift solenoids wirings are faulty. The shift solenoid needs to receive a signal from the Traction Control Unit or Engine Control Unit that the gear needs to be changed and if it notices that the gear needs to be changed, the shift solenoid is supposed to react appropriately. If the shift solenoid is faulty, it won’t be able to receive the signal, or it may not be able to select any gears for changes.
Shifting Problems – if you notice that the gears are having trouble shifting downwards or upwards, this can indicate that there’s a problem with them that needs to be fixed. This can include erratic shifting and it’s when the gears shift up and down sporadically – or it can get stuck on a gear and refuse to change. In this case, you’ll need to fix the wirings between the shift solenoid and the Traction Control Unit.
Stuck in Neutral – for the transmission to shift gears, the shift solenoid needs to regulate the fluid pressure to the correct gear. If the shift solenoid is receiving too much or too little a current from the TCM or the ECU, or the transmission fluid is dirty and it’s caused it to because stuck, then you’ll notice a delay in the gear change or it’ll stay in neutral. The solenoids are connected to the electrical system therefore the ECU will store an error code for the shift solenoid, and this will cause the check engine light to illuminate.
Limp Mode – Limp mode is when there’s a problem with the vehicles computer and it’s unable to receive signals from other sensors. These sensors allow the computer and if it’s not receiving information like the vehicle speed, then it’ll go into limp mode. In limp mode, you may notice the engine misfiring and shaking – this will be felt within the vehicle and you might see the check engine light come on the dashboard. If the problem is with the transmission, you’ll notice that you’ll be locked into one gear so the car won’t be able to rev past a certain RPM and it’ll feel sluggish.
Poor Maintenance
If the brake system hasn’t been maintained, this can cause the solenoid to fail. Maintaining your brakes should be part of your routine maintenance and not doing so can cause you brake problems like the one you’re experiencing now. If you’re not looking after your brakes, it’s very easy for the transmission solenoid to fail and this can be very expensive when looking to replace it at the dealership.
If you want to avoid brake problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.
A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.
How to Fix the Problem
Firstly, you need to figure out what’s wrong – it could either be the wirings, the shift solenoid, TCM or a mechanical fault. To test this, you need to check what the error codes mean, and you’ll need to decode them in order to find out the problem. If the tool tells you that it’s an electrical problem or that the solenoid is stuck, then it’s likely that the problem is with the wiring of the system. To fix this problem, you can lubricate and flush the system with transmission fluid. Transmission fluid can work wonders for the transmission system.
If you get an error saying that the shift solenoid has an electric problem or is stuck, you can use an OBD2 diagnosis tool to test the shift solenoid by forcing the transmission control unit open and closed. To do this:
1. Find the transmission wiring diagram – this can be found in the service manual.
2. Find out the pins that affect the solenoid.
3. Loosen the wiring on the transmission.
4. Start an output test with the OBD2 scanner and test the problematic shift solenoid.
5. Check to see if you get both 12V and ground to the affected shift solenoid at the wiring on the transmissions pin you were testing. If you didn’t get 12V or ground, then you either have bad wiring or a faulty TCM.
Replacing Solenoid
To fix the problems when it comes to the transmission, it can be a problem because various issues can cause the same problem. For example, a bad wiring or sensor could be at fault and not the solenoid itself. If the solenoid is faulty, then it needs to be replaced. Sometimes the solenoid can be integrated into the valve body meaning the part can’t just be replaced, the entire valve body will need to be change – this is common on high vehicles as they usually have TCMs built into the valve body. If you want to replace them, it can be expensive.
Solenoids are located inside the oil pan and are connected to the valve body. Depending on the vehicle you drive, you might need a solenoid pack replacement, or you might need a single solenoid replaced. The mechanic will have to spend between 2-4 hours completing the job and each hour can cost between $60-100 per hours meaning you could spend up to $150 to $400 on just labor itself. If you want to pay for a signal solenoid, it can cost between $15 and $100 and if you want to buy a pack, it can cost between $50 to $300. On average, the whole job can cost between $250 and $600 depending on the vehicle you drive.
To avoid this problem in the future and to stop the shift solenoid wearing out overtime, you can improve the longevity by changing transmission fluid regularly. This will remove all the dirt and sludge that builds up which can damage the shift solenoid if not removed. The plungers within the solenoid need to move in order to pressurize the correct gear – transmission fluid will clean the springs which will make sure that they don’t stick and stop the solenoid from changing gears.