High-Probability Issues:
* Bad ignition switch: This is a common culprit. The ignition switch is responsible for sending power to the starter. If it's faulty, it won't complete the circuit, even with a good battery and starter.
* Neutral Safety Switch: This switch prevents the vehicle from starting unless it's in park or neutral. A faulty switch can prevent the starter from engaging. Check to make sure the shifter is firmly in Park (or Neutral if applicable) and that the switch itself is functioning correctly.
* Faulty wiring: Look for corroded, loose, or broken wires in the starting circuit. This includes the wires connecting the battery, starter, ignition switch, and neutral safety switch. Pay close attention to the connections at the starter solenoid. A visual inspection is a good start, but testing with a multimeter would be more definitive.
* Bad starter solenoid: Even with a new starter motor, the solenoid (the clicking part on the starter) might be bad. If you hear a clicking sound when you turn the key, this is a strong indication of a bad solenoid.
* Poor ground connection: A poor ground connection between the engine block and the battery's negative terminal can prevent sufficient current flow to the starter. Clean and tighten the ground connections.
Less-Likely Issues (but still possible):
* Security system: If your Suburban has a factory or aftermarket security system, it might be preventing the vehicle from starting. Check the security system's indicators for any error messages.
* Immobilizer issue: Some vehicles have an immobilizer that prevents starting if the correct key isn't used. Try the other key if available.
* Alternator (unlikely, but possible): While the alternator charges the battery, a completely failed alternator *might* prevent the starter from getting enough power if the battery is extremely low despite a recent replacement. A voltage test at the battery terminals while cranking would help rule this out.
* PCM/ECM issues (rare): The Powertrain Control Module (PCM) or Engine Control Module (ECM) could have a fault preventing the starter from being energized, but this is less likely unless there are other symptoms.
Troubleshooting Steps:
1. Listen carefully: When you turn the key, do you hear *any* clicks? A single click usually points to the solenoid. No sound at all suggests a problem earlier in the circuit (ignition switch, wiring, etc.).
2. Check fuses and relays: Inspect the fuses and relays related to the starting system in your vehicle's fuse box.
3. Test battery voltage: Make sure the new battery is actually holding a charge and has sufficient voltage.
4. Check the connections: Inspect all connections for corrosion, looseness, or damage. Clean any corroded terminals.
5. Jump start (carefully): Attempt a jump start with another vehicle. If it starts, it points to a charging system or ground issue. However, don't jump start excessively if the battery is new.
6. Use a multimeter: A multimeter is crucial for testing voltage at various points in the starting circuit, identifying faulty components and wiring. This is the most effective way to diagnose the problem definitively.
If you're not comfortable working with car electrical systems, it's best to take your Suburban to a qualified mechanic. They have the tools and expertise to quickly diagnose the problem and make the necessary repairs.
