Automatic gearboxes are more complex than they let on. They are a complex combination of mechanical, hydraulic, and electronic engineering masterpieces that replaced the loved and hated clutch/shift combo of the old.
Automatic Transmission Basics
To understand if you can drive with a bad shift solenoid, you first have to figure out the basic operation of an automatic transmission. Here is a simple breakdown.
- The transmission has mechanical components composed of gears, output shafts, and clutches to channel power from the engine to drive the car.
- A hydraulic system that pumps transmission fluid through channels and valves to control the clutches and gears to determine which gearset and shaft receives engine power
- An electrical system consisting of a computer, sensors, and solenoids to control the hydraulic system and determine when the transmission shifts gear
Now, time to focus on the transmission solenoids.
The solenoids in your gearbox receive signal from the transmission control module (the computer) on where to channel transmission fluid. This makes them the final muscle that actually shifts gears in your automatic transmission.
Your gearbox gets multiple transmission solenoids based on how many gears it has. Most designs have a selonoid count one less than the number of gears you have since First Gear and Reverse Gear don’t use selonoids.
For instance, if you have a five-speed transmission you will have solenoids:
- For first to second shift
- For the second to third shift
- For the third to fourth shift
- For fourth to fifth shift
That makes 5-1 = 4 transmission solenoids.
ProTip: Other modern transmissions might have solenoids for first gear and reverse gear. This is just a generalization on the most common designs in the market.
Can You Drive With a Bad Shift Solenoid?
Yes. A car with a bad shift solenoid will move on first gear – as long as its gearbox doesn’t need a solenoid to go into first. Driving is a different issue. While the car will go into first, shifting into higher gears will depend on the affected solenoid.
For instance, if the first to second gear solenoid is damaged, your vehicle won’t shift into second gear. Driving around first until it skips into third isn’t good for your engine or transmission.
Your car will be more driveable if the faulty solenoid is higher up in the range. For instance, if you have a six speed box and only the final fifth to sixth gear solenoid is faulty, your vehicle will just work on five gears.
You can keep your speed low enough to avoid the final gear or use manual transmission mode to prevent the transmission control module from trying the sixth gear. Expect worse gas milieage as your engine will have to rev more to keep up with the speed it normally does on sixth gear.
Should You Keep Driving With a Bad Shift Solenoid?
No. You shouldn’t be driving with a bad shift solenoid. A car that doesn’t shift as expected is dangerous on the highway. It won’t accelerate as fast as you expect, making passing or pulling away from danger almost impossible.
Moreover, the extra strain of driving at high RPM because your gearbox isn’t shifting on time could wear down both the transmission and the engine faster.
If the solenoid’s failure is catastrophic, keeping the transmission module trying to commune with it could lead to further electrical gremlins or, worse mechanical failure in the gearbox that ruins your gears, oil channels, and clutch rendering the entire gearbox unusable.
What Happens When a Shift Solenoid Goes Bad?
Most car owners rarely have to worry about their transmission solenoids because they rarely go bad. This means you can be caught unawares if it happens to you. Here is a look at a couple of symptoms that hint at a faulty transmission solenoid.
A Check Engine Light
Faulty transmission solenoids will throw an error code. The onboard diagnostic system stores the error codes in the Powertrain Control Module (PCM) and lights up the Check Engine Light. If you have an OBDII scanner, expect the following errors:
- P0750: Shift solenoid problem
- P0753: Electrical abnormally in the transmission shift solenoid A
- P0758: Electrical problem with shift solenoid B
- P0977: A problem with shift solenoid B control circuit
All transmission-related error codes are an emergency. You should have a professional look into your transmission as soon as possible to avoid further damage to the engine and the transmission.
The Transmission Warning Light Comes On
Vehicles with a dedicated transmission warning will send a more detailed message by lighting up this malfunction indicator instead of the check engine light alone. The transmission warning light is a gear icon with an exclamation mark in the middle.
This means there’s a specific and urgent issue with your transmission. Getting a scanner to pull the associated error code will make diagnosis simpler. It could be as simple as low transmission fluid levels or as serious as a damaged transmission solenoid.
Transmission Fails to Shift as Expected
While the above error codes are a confirmation of damage to the transmission, they will often be a reinforcement of other symptoms you can detect when driving.
You might have a faulty solenoid if your transmission no longer shifts as before and seems more unsure. Some of the specific mistakes an automatic transmission makes if it has a faulty or failing solenoid include:
The Transmission Fails to Shift into Some Gears
Remember when we said shift solenoids are responsible for shifting between any set of two gears? If a solenoid responsible for shifting from first gear to second gear fails, then you will never shift from first to second.
Any shift from one gear to another relies on a specific solenoid. Failed solenoids will make shifting up to that gear impossible. It also means you will not shift down from that gear too.
Transmission Keeps Skipping Gears Unexpectedly
When the transmission detects it can’t shift into a specific gear, but the engine speed, vehicle speed, and engine load is low enough, it will skip that gear in favor of a higher gear.
However, before this happens, you will notice:
- The engine will hold onto high revs for a while before eventually shifting and dropping the revs significantly.
- When shifting down, the engine will hold onto high gear for a while, lowering its RPM before eventually shifting to lower gears giving you a spurt of torque, RPM, and perhaps some engine braking in case it drops too far.
If you have ever driven a manual, gear skipping feels like shifting into gear or two lower without rev-matching.
When upshifting, it will feel like skipping a gear or two to choose a higher gear. To do this without stalling or losing power, you will have almost to redline the engine on the current gear to gather as much momentum and RPM as possible to sustain the gear jump.
ProTip: You won’t notice the gear skips when driving downhill since transmissions naturally skip gears to the highest range possible when going downhill
Delayed Shifting
Before your PCM recognizes a bad shift solenoid, it will try to get your transmission into gear using the failing solenoid. It will try for a while before conditions become conducive for the next gear.
The trying period will result in the shift delay and the warning lights. Delayed shifting robs you of torque and horsepower.
It can make a simple highway run dangerous since your vehicle won’t either accelerate to a safe cruising speed or won’t have the power you need to accelerate out of danger when you bury the pedal to the metal.
Stuck in Specific Gear Ranges
If more than one solenoids fail, you can easily find your transmission stuck in a set of gears. For instance, if your final two gears solenoids fail, you will never shift onto the top gears.
For instance, this could be sixth and seventh gear. Your transmission will effectively become a five-speed transmission.
Suppose the damage happens to second to third and third to fourth solenoids. In that case, you could easily be stuck between first and second gear since skipping third and fourth gear to engage fifth gear takes a lot of speed you can’t achieve without redlining the engine – unless you are rolling downhill.
Bad Fuel Economy
Automatic transmissions are all about giving you the perfect balance between power and fuel efficiency.
All the decisions to shift gear aim to give you ideal power while keeping the engine at the lowest RPM possible. If it fails to upshift on time, your engine will rev harder, consuming more fuel.
Such a scenario will lead to terrible gas mileage, especially if the bad solenoids hold you to very low gear ranges.
Weird Noises from the Transmission
If your failing solenoid still works intermittently, chances are it will make weird noises when working. It could also lead to partial gear changes making the cogs and gears in the transmission grind.
Any unexpected noises, grinding, or whining from the transmission accompanied by delayed shifting or no shifting is bad news.
While at times it might be due to low transmission fluid levels, it could also mean one or more solenoids are failing – especially if it happens during gear shifts.
The Transmission Goes into Limp Mode
If things are very bad and you still keep driving, some vehicles have a limp mode coded into the PCM. Limp mode limits the power from the engine and keeps the transmission in low gears, effectively limiting how fast you can drive.
You will get a limp mode warning, and the engine won’t respond to the throttle normally by increasing RPM and power output. You will get enough power to limp at home or the next service center but not enough to drive or use your car normally.
Where is the Shift Solenoid
Shift solenoids sit in different places in or near the transmission. Wherever they are, they must have access to the valves in the transmission or the gears themselves. This makes the most practical place to have a shift solenoid the valve body.
Some car models have shift solenoids accessible without disassembling the valve body, while others require partial transmission disassembly to access the solenoids.
Can a Bad Shift Solenoid Ruin a Transmission?
A bad shift solenoid can ruin a transmission. The damage varies depending on how the shift solenoid failed. If the failing solenoid leaves some debris in the valve body, it could cause blockages to the intricate channels.
The most likely way a bad shift solenoid ruins your transmission is by straining the unit by keeping it in the wrong gears for long.
Bad gears will either spin the transmission faster than necessary in a given gear selection, force the transmission to apply abrupt braking force because the engine RPM is wrong for the selected gear, or lag the engine by holding onto a high gear.
All this unexpected stress can push the transmission beyond expected tolerances – especially if you keep driving without fixing the problem.
ProTip: Running the transmission at high speed on low gears will not only strain the engine but can also overheat the transmission and ruin it.
Can a Bad Shift Solenoid Cause no Reverse?
While most vehicles with a manual shifter don’t need a solenoid for Reverse and 1st Gear since you have to shift the car into Drive or Reverse manually, some modern and fancier cars use solenoids for these gears.
For instance, Range Rovers or Land Rovers with a shift knob or Mercedes cars with a small shift stick that’s not physically linked to the gearbox do all the shifts by wire. This means they won’t go into reverse or drive if the respective solenoid is damaged.
ProTip: Most vehicles with parking assist or advanced self-driving technology are shifting into using solenoids for all gears. The good old days of shifting into first or reverse, even with faulty solenoids or PCM, are in the twilight.
How Long Can You Drive With a Bad Transmission Solenoid?
While your car will keep moving, assuming low gears aren’t affected, driving with one or more bad transmission solenoids is signing the death warrant for your transmission.
You should only keep driving with a bad transmission solenoid to get home or to the mechanic. You can still keep driving if you don’t care for the transmission and the fault is on higher gears. If your gearbox has a manual shift mode, use this to skip or keep off affected gears, as this could make the driving experience more agreeable.