* Low Transmission Fluid: Check the transmission fluid level immediately. Low fluid can cause numerous shifting problems, including inability to shift out of first. Low fluid indicates a leak somewhere in the system – this needs to be addressed ASAP to prevent further damage.
* Faulty Transmission Speed Sensor (or related components): Even though your speedometer is working, a problem with the transmission speed sensor (or its wiring) *could* still affect shifting. The transmission relies on this sensor for proper gear selection. A malfunctioning sensor might provide incorrect data, leading to the transmission staying in first gear. This is less likely given the speedometer is working correctly, as they often share the same sensor in simpler systems, but it’s not impossible for one part of the sensor to be malfunctioning while another is fine.
* Internal Transmission Problems: This is the most serious possibility. Problems within the transmission itself, such as:
* Worn clutch packs: The clutch packs engage and disengage to allow shifting. Wear or damage can prevent them from working correctly.
* Broken or damaged shift linkage: This is the mechanical connection between the gear selector and the transmission.
* Internal valve body problems: The valve body controls fluid pressure within the transmission, dictating gear changes. Problems here can prevent shifting.
* Low fluid pressure: Even with adequate fluid level, low *pressure* due to a pump problem, clogged lines, or other internal issues will prevent proper shifting.
* Transmission control module (TCM) or wiring issues: The TCM is the "brain" controlling the transmission. A faulty TCM or wiring problems leading to the TCM can prevent proper gear selection. This is less likely as it would likely cause a more generalized transmission problem rather than just getting stuck in first. However, it's possible to rule out other things first.
Troubleshooting Steps:
1. Check the transmission fluid level and condition: This is the absolute first step. If low or dirty, this needs immediate attention. Note the color and smell – burnt smelling fluid is a very bad sign.
2. Inspect the transmission fluid lines for leaks: Look for leaks around the transmission pan, cooler lines, and other connections.
3. Have a professional mechanic diagnose the problem: Given the severity of the issue, it's highly recommended to have a transmission specialist or mechanic diagnose this. They have the tools and expertise to accurately pinpoint the problem, avoiding costly guesswork. They can test the fluid pressure, check the TCM, and perform other necessary tests.
Ignoring the problem will likely lead to more extensive and expensive damage to your transmission. Get it checked out as soon as possible.
