1. Safety First:
* Park the vehicle on a level surface and engage the parking brake. Never attempt to diagnose cruise control while the vehicle is moving.
2. Visual Inspection:
* Fuse: Check the cruise control fuse in the underhood fuse box. Your owner's manual will show the location and rating. Replace if blown.
* Vacuum Lines: Many 1997 Tahoes use vacuum-operated cruise control. Inspect all vacuum lines connected to the cruise control servo (usually under the hood near the brake booster) for cracks, leaks, or loose connections. Pay close attention to the line running from the intake manifold. A small leak can significantly impact performance.
* Brake Switch: The brake switch is crucial. If it's faulty, it'll disable cruise control even if everything else is fine. Test the brake switch with a multimeter (continuity should change when the brake pedal is pressed) or replace it if you suspect a problem.
* Clutch Switch (if applicable): Manual transmission Tahoes have a clutch switch. This will also disable cruise control if the clutch is depressed. Test it similarly to the brake switch.
* Cruise Control Switch (Steering Wheel): Visually inspect the switch stalk for any signs of damage or loose connections. Try to wiggle it gently while testing the electrical connections if possible, making sure the connections are secure. Replacement is often necessary if faulty.
3. Testing (Requires a Multimeter):
* Cruise Control Servo: This is the actuator that controls the throttle. With the engine running, check for vacuum at the servo. If there is no vacuum, trace the vacuum line back to the source. If vacuum is present, testing the servo itself usually requires specialized tools or a known good servo for comparison.
* Speed Sensor: The speed sensor input is critical. A faulty sensor will prevent the cruise control from engaging. Its location varies depending on transmission type, consult your repair manual. Often found near the transmission or differential. You'll need to test the voltage output of this sensor with a multimeter while the vehicle is running. Compare your reading to factory specs found in a repair manual.
* Wiring: Check for broken or corroded wires in the cruise control system harness. Pay close attention to areas where wires are subject to movement or abrasion (e.g., near the steering column). A wiring diagram is essential for tracing the circuit.
4. Advanced Diagnostics:
* OBD-II Scanner: While some cruise control issues won't trigger a diagnostic trouble code (DTC), a scan tool can rule out other related issues that might be preventing cruise control from working.
* Professional Mechanic: If you're not comfortable with electrical testing or vacuum system diagnosis, it's best to take your Tahoe to a qualified mechanic. They have the tools and expertise to properly diagnose and repair the problem.
Important Notes:
* Repair Manual: A repair manual specific to your 1997 Chevy Tahoe is invaluable. It contains wiring diagrams, component locations, and troubleshooting steps that are essential for accurate diagnosis.
* Vacuum System: Vacuum leaks are common culprits in older cruise control systems. A smoke test of the vacuum lines can help pinpoint leaks.
By following these steps methodically, you should be able to isolate the problem with your Tahoe's cruise control. Remember safety is paramount, and if you're unsure about any step, seek professional assistance.
