There are a few erratic behaviours a car demonstrate that car owners definitely dread. However, Iâd vouch that none feels quite as intimidating as a transmission-related issue. Transmissions are expected to last as long, if not longer than the engine itself. However, modern complications have made transmission reliability a top concern for car buyers.
Transmission failures can be catastrophic, leaving you stranded while racking up exorbitant repair costs. Thankfully though, transmissions rarely fail outright without any signs. Typically, they demonstrate signs of failure way before they give up entirely. By paying close attention to those symptoms, you can avert the fault from further developing.
Because there are various types of transmission, weâll be emphasizing one of the most commonly found in most modern cars nowadays. Many of todayâs cars come with an automatic transmission. In fact, some manufacturers have deviated from twin-clutch units in favour of automatic transmissions.
Inside An Automatic Transmission
Itâs important to note that for an automatic transmission to function optimally, a multitude of parts has to work together in unison. First, you have the actual transmission housing itself that contains the core of a transmission unit. Inside the housing are many sets of clutch packs and various planetary geartrain.
For an automatic transmission to change gears, all the gear sets have to engage and disengage in a certain predetermined order. Just by changing the planet carrierâs drive method, 3 different gear ratios can be produced. So an automatic transmission has different combinations of planet gear sets for drivable gear ratios.
This is why an automatic transmission can remain relatively small yet be built with 10 forward gears in modern cars. To engage and disengage the various gear sets, transmission fluid pressurises and releases the clutch packs. The distribution for transmission fluid inside an automatic transmission is managed by the valve body.
The valve body is essentially a maze filled with tens upon hundreds of fluid channels. The valve body is constantly submerged and fed with transmission fluid during its operation. Inside the valve body are springs and solenoids that operate jointly to pressurise and change the path for the transmission fluid to flow through.
Of course, with solenoids, you need a computing unit to energise them. Thatâs the transmission control unit or electro-hydraulic controller unit. In some transmissions, this controller is incorporated directly within the valve body itself. Just by manipulating the various transmission solenoids, the automatic transmission can switch gears autonomously depending on the driving conditions and needs.
Therefore, you can imagine the shift solenoids as the heart of the transmission unit, and the valve body as the arteries. If something goes wrong with the solenoid operation, your transmission wonât be able to shift properly or shift at all.
How Do Transmission Solenoids Work
Solenoids operate by gradually building current from resisting voltage flow. The greater the current, the stronger the magnetic field. When this magnetic field is strong enough, itâll operate a plunger which in turn changes the fluid flow path. There are also pressure regulating solenoids in a valve body that alters the fluid pressure for different conditions.
The transmission control module is sometimes referred to as an electro-hydraulic controller since the transmission solenoids are fundamentally hydraulic valves that operate electronically. The TCM has to switch the various solenoids on and off at the right time for ideal transmission shifting.
Therefore, the whole operation of an automatic transmission shifting process can actually be simplified. Your main engine computer coordinates with the ABS computer to deliver driving information to the transmission control unit. This information includes factors such as vehicle speed, throttle position, engine rpm, etc.
Then, all the pertinent details necessary to determine shift behaviour is compiled and further analysed by the transmission controller. This also includes driver demand, such as sport mode or manual shifting. The transmission controllerâs job is to turn that information into solenoid operation.
Itâll switch the shift solenoids accordingly to achieve its objective. When the solenoid receives the switching signals from the transmission controller, it engages the spring-loaded plungers and alters the transmission fluid travel path. The fluid travels through the channels inside a valve body and flows toward the respective clutch packs and bands.
The pressurised clutch packs will, in turn, engage the gear sets. By designing how and when each planetary gear set engages, multiple desirable gear ratios can be derived from just a few gear sets. In transmissions with a physical transmission selector lever, the lever actually operates a mechanical valve within the valve body that also modifies the fluid flow path.
Shift Solenoids Symptoms or Failure
Obviously, the transmission solenoids play a huge part in a transmissionâs operation. Itâs not acceptable for even one of the solenoids to fail, as it will cause improper shifting and rough operation of the transmission.
However, in most cases, solenoids rarely do fail outright. Over time, shift solenoids start to wear out and might not manage optimum capabilities. When this happens, the plungerâs switching time might be delayed or just undesirable. Therefore, shifting action might not feel as smooth and prompt compared to a new transmission.
Poor Shifting Quality
When a transmission solenoid fails, youâll most definitely notice the impact on shift quality. Each solenoid is responsible for different tasks, and the transmission only shifts neatly if everything happens together. This means there isnât a solenoid for every gear, so you just lose that gear in particular.
What actually happens when a solenoid isnât functioning correctly is a single clutch pack might not be engaged or disengaged on time. This clutch pack might be responsible for multiple gears in an automatic transmission.
When a clutch pack isnât being pressurised to specifications, it translates directly to the shift operation. What youâll perceive are delayed shifting, jerky shifting or even gears slipping out. In some cases, the car might not shift into certain gears at all.
If your transmission is slipping in every single gear, this can mean that thereâs trouble with the pressure regulating solenoid. In severe cases, a failure with this solenoid can cause your transmission to give up entirely.
Typically, the effects are felt in both ways. This means that it can also affect the downshifting of the transmission. The transmission might refuse to downshift altogether, leaving you stuck in neutral. With that said, a solenoid thatâs only starting to go bad might not produce any symptom at all.
Check Engine Light (and Automatic Transmission Warning Light)
If thereâs something thatâs obviously wrong with your car, then it should trigger a check engine light. In some cars though, there will even be an automatic transmission warning light. By this stage though, you should definitely visit a local workshop to get it sorted.
With that said, if you own an earlier car, especially one built before the advent and popularity of clutch-operated transmissions, there might not be any engine code defined for transmission faults. This is because earlier transmissions are generally mechanical, with very few electrical components inside. This means that transmission abnormalities are not monitored as thoroughly.
This is in contrast to modern automatic transmissions. There are more electrical parts within with an external transmission control unit monitoring the transmission performance. Factors such as clutch filling times and pressure are a major element for ideal transmission shifts.
These are monitored so the transmission controller can adapt to clutch pack wear and tear. If the filling times are out of specification, itâll flag a trouble code. On newer automatic transmissions, the transmission controller is typically incorporated into the valve body or within the ECU.
The transmission error code will also help your technician to determine the problem quickly and effectively. Therefore, if your choppy shifts are accompanied by a check engine light, then a workshop visit is way overdue.
Itâs also worth noting that when thereâs an automatic transmission related issue, thereâs a good possibility that your car will enter âlimp-home modeâ. When this happens, the automatic transmission will default to a single drive gear, normally gear 2 or 3, so you can drive it as long as possible to the workshop.
This is mainly to prevent further damage to the transmission. Itâs easy for a slipping transmission to start overheating due to the excess heat produced by friction from the clutch packs. This ingenuity of a default drive gear is made possible thanks to the properties of solenoids. A solenoid can be normally open and closed.
If those solenoids are not energised, the transmission fluid flow then defaults to a safe state. The fluid pressurised the necessary clutch packs to shift to the default gear.
Low Power, Odd Car Behaviour
A poorly performing transmission would also behave strangely in general. This can heavily impact the drivability of your car. In some cases, the transmission might excessively rev out a single gear in particular before shifting to the next.
Itâs also possible that your car will shift into the gear fine, but itâll constantly slip out of gear whenever you apply power. This is a sign that the transmission fluid pressure is insufficient to keep a clutch pack engaged under load.
When the transmission does shift into gear, it might be very rough and sudden. Itâll feel like a manual transmission car when you release the clutch too quickly. Sometimes this might be mistaken as an engine thatâs hesitating or struggling, when in fact itâs a transmission fault.
What Should You Do If You Think You Have A Bad Shift Solenoid
It can be daunting when youâre faced with a transmission-related issue. Especially when youâre unfamiliar with the mechanics of an automatic transmission. This can be problematic especially if your car remains seemingly drivable. It tricks you into a sense of security.
When youâre dealing with a transmission related issue, itâs best that you consult a workshop as soon as possible. This is made easier if your car can still be driven. Donât attempt to use your car as it is for your day-to-day commute.
Itâs advised so because a transmission issue can quickly snowball into catastrophic transmission failure. By that time, a simple solenoid replacement or even transmission fluid change may not remedy your issue anymore. Due to the nature of an automatic transmission, itâs quite delicate.
This stands true if you have an older car without transmission-related error codes that can appear. You should recognise the symptoms of a faulty transmission and consult a local workshop as soon as possible. That said, older band-type transmissions with mechanical valves can last a long time even when neglected.
Once you experience the aforementioned symptoms, drive gingerly to the workshop. Do not put too much load on the transmission. If needed, you can always manually select a gear thatâs not slipping and stick with that gear. Itâs important that you avoid overheating your transmission when you have low fluid pressure.
A quick check you can perform is to inspect your transmission fluid level. Make sure you still have adequate transmission fluid and itâs not overfilled. Either can cause serious shifting issues. That said, on some newer cars, manufacturers have eschewed the transmission dipstick, some even removed the tube altogether. You need a diagnostics scanner or a special tool to check the transmission fluid level in this case.
If you have low fluid levels, check whether if youâve developed a transmission fluid leak. If itâs alarmingly low then itâs possible that you mightâve hit your transmission fluid pan and caused it to crack. You should stop driving and ask for a tow service when this happens.
What Can Cause A Bad Transmission Solenoid Or Shift Issues
It needs little reiterating, but failure comes with age. The transmission solenoids reside within an intricately self-contained system that can be tough on any electrical system. Over time, the solenoids, being continuously bathed in transmission fluid, can clog up with foreign particles. This causes performance issues with the solenoids, changing how the fluid flows.
The issue with an automatic transmission is that the valve body itself consists of tiny oil channels. The tolerances for dirt or excessive metal shavings within the oil channels are minimal. Shift solenoids themselves incorporate a small filter web to reduce chances of failure. Regardless, over time the buildup of minuscule particles on the solenoids can cause shift issues.
Although rare, itâs also entirely possible that the solenoids have just stopped working. Coil windings can degrade over time, reducing the magnetic strength. It can even be an internal open circuit or short within the solenoid causing a failure.
Itâs worth noting that your transmission issues may begin to surface the moment you change your automatic transmission fluid. This can happen from reasons to improper fluid level, incompatible fluid, or just dirty transmission fluid being introduced. Be sure to check the fluid level yourself once you get it changed.
Newer transmissions might require a bleeding process once youâve performed a repair on your transmission, or just replaced the fluids. This is typically accomplished via a diagnosis system. This is required because air within a hydraulic valve system can actually airlock the system. Automatic transmissions do have a vent that facilitates self-bleeding processes though.
Also, this might not be entirely obvious, but fluid contamination can also be a huge problem. Most people would think that this wouldnât be a problem, as long as you keep tab on your transmission fluids. However, some transmissions implement a transmission fluid cooler into the coolant radiator.
Therefore, when this transmission fluid cooler starts to leak, coolant can quickly enter and circulate within the transmission. As you can imagine, transmission fluid stops being effective once itâs contaminated with coolant. When this happens the transmission fluid turns into a milky color.
Determining Whether You Have Shift Solenoids Symptoms
The issue with transmission related issues is the fact that the system works as a whole, and once thereâs a problem with it, itâs difficult to pinpoint the issue. The process can be simplified if itâs a modern automatic transmission with error codes that can help determine the fault.
However, it always helps to start from the easiest issue first. The transmission fluid is behind the main operation of any automatic transmission. Therefore, always check your transmission fluid first. That said, it might not be possible to check the fluids yourself. As mentioned prior, you might need a special dipstick that can be bought online or a scan tool.
If possible, drain your own transmission fluid so you can get an idea of your transmissionâs condition. You can also use a paper towel to sample your fluid condition to compare it against other examples online. You shouldnât find too much metal shavings on it, which can indicate internal transmission damage.
If your transmission fluid seems fine, then a diagnostics scanner is needed in most cases to perform in-depth diagnosis. In earlier automatic transmissions though you can find wiring information online and attempt to diagnose the actuation of the solenoid by directly applying voltage to it.
Otherwise, diagnostic scanners can be used to remotely activate the solenoids. A solenoid thatâs operating normally should produce an audible clicking sound. This can rule out the fact that you might have a malfunctioning solenoid, although in newer cars that should trigger a fault code.
If the solenoids operate fine, then a valve body removal is necessary for further diagnosis. Removing the valve body can reveal a lot about your transmission. Some might prefer to leave this job to the workshop though. Itâs a bit more involved than replacing the transmission fluid.
In general, automatic transmission issues are relatively scarce. If you start experiencing shift issues early into your car ownership, then you should suspect that itâs a recurring concern with the automatic transmission itself. You can find this information online, just search for similar complaints from other owners.
It might be a design flaw that the manufacturer itself has issued a service recall for. In some cases though, the problem might just be widespread enough that you can find it online. A case like this can be observed with Volkswagen and their DSG 7-speed transmission. The dry clutch within failed so frequently that Volkswagen had to acknowledge there is an error with the transmission design.
Is Replacing A Bad Transmission Solenoid Diy-friendly
Thankfully, if youâve narrowed the fault down to the transmission solenoid, the job to replace it is not all too difficult. You have to ensure that you have the appropriate spare part and tools before committing to the job though. A diagnostic scanner is typically not mandatory when replacing a shift solenoid. Youâll need a floor jack and jack stands for this.
A workshop manual will be a big help here. Itâll provide information on the tightening torque, specific steps required, filling capacity, etc. With that said, even without documentation, it shouldnât be too tricky to do on your own.
Before you undertake the job, make sure you have a drain pan at hand. You should also prepare towels as it can get quite messy. Youâll want to replace the transmission fluid and filter while youâre inside the valve body too. Spare an afternoon to carry out the job as well. If youâre ready, jack up your car and prepare the drain pan.
The first step is to drain off your transmission fluid. You should be able to source a guide on this for your particular car model online. Normally, all you have to do is to remove the drain nut from the transmission fluid pan. Some cars (notably Mercedes-Benz models) might have an overflow pipe that you need to poke out to fully drain the fluid though.
After youâve drained the fluid clean, youâll have to remove the transmission fluid pan. Depending on the car model, this can be either simple to relatively complicated. Some cars have very limited access to some screws affixing the pan to the transmission housing.
Youâll reveal the transmission fluid filter. Remove the filter to gain access to the valve body. Before you eagerly remove the valve body, disconnect the main transmission electrical connector on the outside. Ensure you remove the selector lever as well while taking note of the position.
There will be several bolts holding down the valve body, typically at the same length and possibly colour-marked. Remove these screws and carefully drop the valve body. Itâll be quite heavy.
Ensure that work performed on the valve body is done somewhere clean and sterile. Wear a pair of clean lint-free gloves while removing the transmission solenoids. While youâre replacing the faulty solenoid, it makes sense to remove the other solenoids for a clean. Just rinse them in clean transmission fluid.
All in all, itâs not an overly complex job. Make sure you have the correct solenoid, normally these are also colour-marked. Be mindful and avoid dirtying the valve body, itâs an intricate part. If youâre mechanically competent, this job is entirely achievable in your own shed with only basic hand tools.
