How do You Fix an Automatic Transmission Not Shifting

Whether they are cars, trucks, or SUVs, today's vehicles are technical wonders. On difficult road surfaces, they provide smoother rides, faster acceleration, and better handling.

Transmission problems may still be a source of annoyance, even if technical developments have boosted the general dependability and lifespan of these everyday drives.

Additionally, identifying and resolving transmission issues can be difficult for skilled mechanics due to the intricacy of contemporary transmission technology.

If your car has an automatic, manual, or direct drive gearbox, it still depends on several different parts that all work together flawlessly to move your car forward. Problems with the transmission might originate from a number of different places.

In this post, we will examine the top three typical causes of a car's refusal to engage gears while the engine is running. We will also discuss a few common reasons why a transmission would not engage in any gear or shift correctly.

In order to lessen the impact on your finances, we will also offer advice on the activities you can undertake to resolve these problems immediately.

How to Diagnose the Issue

According to car statistics, approximately 96 percent of daily drivers use automatic transmissions. Therefore, this article will primarily focus on automatic gear drive systems, with a brief discussion of manual transmissions to follow.

An automatic transmission is a hydraulic unit composed of a series of components including lines, gears, and valve bodies. This intricate system gradually transmits power from the engine to a torque converter, through the valve body to the driveshaft, and ultimately to the axle.

When your vehicle fails to engage a gear or does not move forward or in reverse when placed in gear, the root cause typically stems from one of these three sources:

An electrical problem

Automatic transmissions rely on a network of sensors, switches, and electrical wiring to communicate with the vehicle's onboard computer. In many instances, a minor electrical issue can disrupt this communication, preventing the transmission from engaging.

A clogged hydraulic system

Most modern automatic transmissions, including CVTs (continuous variable transmissions), require proper fluid levels and clean fluids.

These fluids are essential not only for maintaining hydraulic pressure but also for keeping the transmission cool. The presence of debris in the system can obstruct the lines and impede efficiency.

A mechanical failure

Surprisingly, the least common source of transmission issues is mechanical damage to internal components.

Why Won't My Car Shift into Gear?

In order for an automatic transmission (AT) to shift into gear, various hydraulic, electronic, and mechanical systems must work harmoniously together.

When one or more of these systems encounters a failure, your car may refuse to shift into gear. To help identify whether your vehicle requires the attention of a specialist, let’s explore some reasons why your car might not engage in gear:

Transmission Fluid

An automatic transmission with low or contaminated fluid may struggle to shift into gear. Automatic transmission fluid (ATF) should exhibit a light red or pinkish color.

Dirty ATF, ranging from deep red to dark brown, loses its ability to adequately lubricate and cool internal components, resulting in excessive wear and premature part failure.

Check your owner's manual to locate the transmission dipstick and identify the appropriate ATF for your vehicle's make, model, and year. With the AT in park, engine running, and warmed up, the ATF level should fall between the "full" and "add" marks on the dipstick.

If the fluid is low, add new ATF using a clean funnel. If your car shifts into gear after adding ATF, it likely had low fluid due to a leak. Visit your repair shop to identify and address any leaks and consider flushing the ATF and replacing the filter.

Electronic Sensor

A malfunctioning electronic AT selector switch can fail to signal the engine control module (ECM) that you have shifted your car into gear, preventing the shift solenoids from operating.

Slowly moving the shifter from park to low several times might help remove corrosion from the switch's contacts and allow you to proceed. Leave transmission electronic diagnostics to transmission specialists.

Gears

Misaligned, damaged, or stripped-out gear sets can impede the smooth engagement of gears, preventing your vehicle from shifting into gear.

These issues are typically caused by worn gears, failing bearings, or internal seal or O-ring leaks. Gears grinding against each other during gear selection produce noise and generate metal dust and chips that can harm other transmission components.

Leave internal transmission repairs to professionals, and to prevent future transmission problems, insist that your mechanic thoroughly flush the transmission case, valve body, and radiator cooler with solvent during any transmission repair.

Linkage

Misadjusted, damaged, or stretched shift linkage or cables can hinder the shifter's movement and prevent the AT from shifting into gear.

Some vehicles have adjustable shift cables, so consult your owner's manual for guidance on adjustment. Adjusting a cable is a one-time fix you can perform before seeking professional service.

However, ensure the adjustment does not allow your car to start in gear, as it could lead to sudden movement.

Other Causes

Check whether the engine is running, the foot is on the brake, the battery is fully charged, and the check engine light (CEL) is illuminated.

A faulty charging system can result in a weak or dead battery, preventing the shift interlock from disengaging or shift solenoids from engaging.

Depending on the cause of the CEL, it may prevent the ECM from operating the shift solenoids and shifting gears. Have your mechanic inspect these potential issues if they are preventing your car from starting or shifting into gear.

Practical Solutions for Automatic Transmission Not Shifting

Address transmission fluid issues

Begin by verifying the transmission fluid's level and condition. If the fluid is low, top it up to the correct level. If the fluid appears dirty or burnt, it is advisable to replace it.

Inspect and adjust the transmission shift cable

Examine the shift cable for any signs of misalignment or damage. If issues are detected, make the appropriate adjustments or, if necessary, replace the cable.

Resolve transmission control module (TCM) problems

Should the problem be associated with the TCM, resolving it may involve tasks such as reprogramming, updating, or replacing the module. Seek assistance from a qualified technician to perform these procedures.

Replace worn or damaged transmission components

Thoroughly inspect the transmission's internal components, including clutch plates, bands, and solenoids, to identify any wear or damage. Replace these components as needed.

Consider transmission rebuilding or replacement

In cases of extensive damage, it may be prudent to contemplate either rebuilding or entirely replacing the transmission unit.