1. Identify the Vehicle Speed Sensor (VSS):
* Location: The VSS on a 1999 Camaro 3.8L is typically located on the rear of the transmission. It's a small sensor with a single wire connector. Consult a repair manual (Chilton's or Haynes) for a precise diagram. This is crucial, as the location can slightly vary depending on the specific transmission.
2. Visual Inspection:
* Check the connector: Carefully inspect the VSS connector for any signs of damage, corrosion, loose wires, or broken pins. Clean the connector with electrical contact cleaner if necessary.
* Examine the wiring: Trace the wiring harness from the VSS back to the PCM (Powertrain Control Module). Look for any signs of chafing, cuts, or breaks in the wires.
3. Testing the VSS:
* Ohmmeter Test (best approach): You'll need a multimeter. Disconnect the VSS connector. With the ignition OFF, measure the resistance across the sensor's terminals. Your repair manual will give you the correct resistance specification for your VSS. A reading outside the specification indicates a faulty VSS.
* Backprobe Test (requires caution): You can attempt to backprobe the VSS signal wire (with the ignition ON) while rotating the rear tire. You should see a fluctuating voltage signal on your multimeter. This test is less reliable and should only be attempted if you are comfortable with automotive electrical systems. Improper backprobing can damage your vehicle's electronics.
4. Testing the Wiring:
* Continuity Test: If the VSS tests good, you need to test the wiring for continuity between the sensor and the PCM. Disconnect both ends of the wiring harness at the VSS and the PCM connector. Using your multimeter, check for continuity between the wire(s) at each end. A lack of continuity indicates a broken wire somewhere in the harness.
5. Possible Solutions Based on Testing:
* Faulty VSS: Replace the VSS with a new one from a reputable auto parts store. Be sure to get the correct part number for your specific transmission.
* Damaged Wiring: Repair or replace any damaged wiring in the harness. This may require splicing in new wire sections.
* Faulty PCM: While less likely, a faulty PCM can also cause speedometer issues. This is usually only diagnosed after all other components have been ruled out. PCM replacement is a more complex and expensive repair.
* Cluster Issue (less likely): It's possible, though less probable given that other gauges work, that there is a fault within the instrument cluster itself. This would require more specialized testing equipment.
Important Considerations:
* Repair Manual: A repair manual specific to your 1999 Camaro is highly recommended. It will provide detailed diagrams, specifications, and procedures for testing and replacing components.
* Safety: Disconnect the negative battery terminal before working on any electrical components.
* Professional Help: If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. Incorrect procedures can lead to further damage.
By systematically following these steps and using a multimeter, you should be able to diagnose the problem and repair your speedometer and odometer. Remember to always refer to your repair manual for specific instructions and diagrams relevant to your vehicle.
