Here's a breakdown of potential causes and what you should do:
* Shift Solenoids/Valve Body: These are electrical components that control the hydraulic pressure within the transmission, directing fluid to engage different gears. A faulty solenoid or a problem with the valve body itself (which houses the solenoids) can prevent proper shifting. This is the most likely culprit given your description. A mechanic can test these components.
* Transmission Fluid: Low, dirty, or incorrect transmission fluid can cause shifting problems. Check the fluid level. It should be checked with the engine running and warmed up. If it's low, add the correct type of automatic transmission fluid (refer to your owner's manual). If it's dirty or burnt-smelling, a complete fluid and filter change is needed. This is a relatively inexpensive first step.
* Transmission Linkage (Less Likely): Although less likely given your intermittent shifting, a problem with the transmission's linkage could interfere with gear selection. This is less probable because your issue is more about skipping gears than not engaging them at all.
* Speed Sensor (Less Likely): A faulty vehicle speed sensor might confuse the transmission's computer, preventing it from shifting correctly. This is less likely as it usually leads to other problems as well, like incorrect speedometer readings.
What You Should Do:
1. Check the Transmission Fluid: This is the easiest and cheapest thing to check first. If it's low, dirty, or burnt, address that immediately.
2. Seek Professional Help: Given the intermittent nature of the problem and the skipping of gears, taking your Mustang to a reputable transmission specialist or mechanic is strongly recommended. They have the tools and expertise to diagnose the issue accurately and perform the necessary repairs, which may involve replacing solenoids, rebuilding the valve body, or even a more extensive transmission overhaul depending on the diagnosis.
Do NOT: Continue driving the car extensively with this problem. Driving with a malfunctioning transmission can cause further damage and lead to a much more expensive repair.
Ignoring the problem will likely worsen it and potentially lead to complete transmission failure. Get it checked out soon.
