Signs You’ve Got a Bad Shift Solenoid
Signs of a failing shift solenoid
These solenoids operate submerged in transmission fluid and fail primarily from repeated hot-and-cold cycling in this harsh environment. Mechanical failures can also occur. Shift solenoids will also just wear out over time, but getting your transmission serviced at the recommended intervals listed in your owner’s manual can help prevent them from sticking.
If you notice any of the following symptoms of a faulty shift solenoid, get your car to a mechanic right away. Avoid any highway use and have it towed, if necessary. If you leave it unchecked, your transmission can get damaged, which will lead to a very costly repair bill.
The check engine light comes on: The TCM continuously monitors shift solenoid operation. If it detects a problem with one of the solenoids or the related circuits, it will send a request to the engine’s computer to turn on the check engine light.
Erratic shifting or shift slippage: The shift solenoids regulate the flow of hydraulic fluid for shifting. A problem with one or more of the solenoids can cause a lack of pressure, resulting in hard, soft or delayed shifts. A failed shift solenoid can also cause transmission slippage, where your engine revs faster but the car stays at the same speed.
Transmission won’t shift gears: 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.
Vehicle stuck in limp-home mode: If the TCM determines there’s a problem with a shift solenoid, it may put the vehicle in “limp-home mode.” In this state, the transmission will be forced into second or third gear to limit your speed, and one or more warning lights will appear on the dash
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How to fix the problem
Diagnosis is key when it comes to transmission problems, as various issues can cause similar problems. Trouble with wiring or sensors could be at fault instead.
A faulty shift solenoid should be replaced. In some cases, the solenoid is integrated into the valve body and isn’t serviceable. This means the entire valve body will need to be swapped out.
Some high-end vehicles also have the TCM built into the valve body. Replacement of these units can be pricey. After any of these repairs, the TCM may need to be reprogrammed.
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What does the shift solenoid do?
As you drive, the car’s computer determines which gear is optimal for your speed. The transmission control module (TCM) — the brains of the transmission — will send power to one of the shift solenoids in order to shift gears.
Inside the solenoid, there’s a plunger surrounded by a magnetic coil. When the TCM triggers this coil, the plunger moves, allowing pressurized hydraulic fluid to flow to certain parts of the transmission. This allows the transmission to shift into the desired gear.
There are two or more shift solenoids inside your transmission. The solenoids are typically integrated into the transmission valve body. If one or more of them fails, you’ll likely notice a handful of car problems.
About the Author
Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.
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