High-Probability Issues:
* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation. A faulty CKP will prevent the engine from starting because the computer can't time the fuel injection and ignition properly. This is a common failure point on many vehicles, especially older ones.
* Cam Position Sensor (CMP): Similar to the CKP, but for the camshaft. A faulty CMP will also prevent starting.
* Ignition Switch: This might be worn out or failing, preventing power from reaching the necessary components to crank the engine. You might hear nothing when you turn the key, or only a click.
* Fuel Pump: A failing fuel pump might not deliver enough fuel to the engine, causing it to stall and then fail to restart. You might hear a weak "whirr" from the pump when you turn the key to the "on" position (but not cranking).
* Alternator: A failing alternator won't recharge the battery. If the battery is already weak, the engine might stall. Testing the alternator's output voltage is crucial.
Medium-Probability Issues:
* Battery: A weak or dead battery will prevent starting. Though less likely if it was running before stalling, a sudden voltage drop might have drained it. Test the battery voltage.
* Mass Airflow Sensor (MAF): A faulty MAF sensor can cause the engine to run poorly or stall, but it's less likely to be the *sole* cause of a complete no-start condition.
* Throttle Position Sensor (TPS): Similar to the MAF sensor; a malfunctioning TPS can disrupt engine operation, but a complete no-start is less common.
Low-Probability Issues (but still possible):
* Wiring Problems: Damaged or corroded wiring anywhere in the ignition, fuel, or engine control systems could be the culprit. This requires thorough investigation.
* Engine Control Module (ECM) / PCM: The computer itself could be faulty, though this is less frequent.
* Fuel Injectors: While unlikely to cause an immediate stall and no-start, clogged injectors could contribute to the issue.
* Security System: If the vehicle has an aftermarket or factory alarm system, it might be interfering.
Troubleshooting Steps:
1. Check the battery: Test the voltage with a multimeter. A reading below 12.6 volts indicates a weak battery.
2. Listen for the fuel pump: When you turn the key to the "on" position (but before cranking), you should hear a brief humming sound from the fuel pump.
3. Check fuses and relays: Inspect the fuses and relays related to the fuel pump, ignition, and engine control system.
4. Try jumping the battery: If the battery is weak, a jump start might temporarily resolve the issue (but a weak battery could still be the underlying problem).
5. Have it scanned: A diagnostic scan tool (OBD-II scanner) can read trouble codes from the engine control module, which will point to specific faulty components.
Important Note: Since safety is paramount, if your Tahoe stalls while driving, pull over to a safe location as soon as possible. Do not attempt repairs on the side of a busy road. It's best to have a qualified mechanic diagnose and repair the problem, especially if you lack experience working on vehicles. Ignoring a potential problem could lead to more serious and expensive damage.
