* Speedometer: Obviously, this is the direct connection. No signal, no speedometer reading.
* Transmission Control Module (TCM): The TCM uses VSS input to determine the appropriate shift points. Without this information, the transmission may default to a safe mode, often resulting in delayed or incorrect shifting, or even staying in a single gear.
* Electronic Control Module (ECM): The ECM also uses the VSS signal for other functions like cruise control and fuel injection timing.
Other possibilities (less likely, but worth considering):
* Transmission problems: While less likely given the simultaneous speedometer failure, internal transmission problems *could* cause both issues. However, these usually manifest with other symptoms like slipping, hard shifting, or unusual noises.
* Wiring harness damage: A damaged wire between the VSS and the TCM/ECM could interrupt the signal. Look for broken or frayed wires near the transmission and under the vehicle.
* TCM/ECM failure: Though less common, a malfunctioning TCM or ECM could also cause these issues, but it's less probable than a VSS problem.
Troubleshooting Steps:
1. Check the VSS: This is the most likely culprit. The VSS is usually located on the transmission; its location varies slightly depending on the specific transmission in your Lumina. You might need to consult a repair manual or online resources with diagrams for your model. Inspect the sensor for any physical damage. The most straightforward test is to replace the VSS. They're relatively inexpensive and easy to replace (though you might need some basic mechanical skills).
2. Check the wiring: After replacing or inspecting the VSS, visually inspect the wiring harness leading to it and to the TCM/ECM for any damage.
3. Professional diagnosis: If you're uncomfortable working on the vehicle yourself, take it to a mechanic for a proper diagnosis. They can use a diagnostic scanner to read any transmission or ECM codes that might pinpoint the exact problem.
Important Note: Driving a car with transmission issues can cause further damage. If the shifting problem is severe, avoid driving the vehicle until it's repaired.
