The Symptoms of a Bad Transmission Solenoidby TJ Hinton
Your transmission shift solenoids mount on the transmission valve body that controls fluid flow through the various circuits and passages in the transmission. The solenoid plungers are constantly bathed in fluid from the transmission, and metal salt from the manufacturing process and normal wear, as well as detritus from the friction materials can collect on the plungers and cause them to bind in their bores and fail to function properly. Identify these failures by the symptoms they produce.
Your transmission relies upon the positions of multiple solenoids to control the gear selection. If one or more solenoids are bad, you may lose the use of one or more gears, and may even be stuck in one particular gear or unable to shift into any gear at all. Do not confuse a slipping transmission with a solenoid problem. You will hear and feel the difference when you try to shift. A slipping transmission will actually shift, but then not produce any power once in gear, whereas a bad solenoid will prevent the shift from occurring in the first place.
Most modern vehicles have some sort of transmission control module that monitors the transmission through various sensors, such as the shift-position sensor and the transmission speed sensor. Additionally, the TCM and solenoid wiring are protected by fuses. Any failure in the fuses, sensors or associated wiring can result in conditions that prevent the solenoids from working properly.
The TCM will detect failures within the systems that it monitors and any failure, from a bad solenoid to a blown fuse, will trigger a limp-in mode designed to prevent further damage to the transmission while allowing some limited capacity to travel. Typically, the limp-in mode will place the transmission into second gear and keep it there. This leads to a sluggish feeling when initially accelerating from a standing stop, and high engine revolutions when traveling faster than around 30 mph. This is meant to be used to return home or to a service center if a failure occurs. Do not continue to use the vehicle before rectifying the problem that triggered the limp-in mode.
Diagnostic Trouble Codes
Once the TCM detects a problem in the monitored systems, it sets a diagnostic trouble code that can be retrieved using a scan tool appropriate for the year and make of the vehicle in question. The trouble codes for transmission control components begin at P0700, and the codes specific to the solenoids range from P0751 through P0758. Additionally, there are speed sensor codes that run from P0500 through at least P0503. Check the DTCs against the model-specific codes set forth by the manufacturer.
TJ Hinton trained as an auto mechanic at Mississippi Gulf Coast Community College and then later graduated from MMI as a certified motorcycle mechanic . He's also worked for 20+ years in home construction, remodeling and repair. His articles appear on InternetAutoGuide.com and TopSpeed.com.