* Starter Solenoid: This is the most probable cause. The solenoid engages the starter motor. If it's sticking, heating up, or has a bad connection, it might not engage the first time but will after cooling down slightly (when you turn the key off).
* Starter Motor: The starter motor itself could be failing. Similar to the solenoid, it could be struggling to turn over the engine on the first attempt due to worn brushes or other internal issues.
* Battery Connections: Even with a new battery, loose or corroded connections at the battery terminals or on the starter motor can cause intermittent starting problems. A clean and tight connection is crucial.
* Ignition Switch: While less likely given the specific symptom, a failing ignition switch could intermittently fail to send power to the starter.
* Neutral Safety Switch (Automatic Transmission): This switch prevents the car from starting unless the gear selector is in Park or Neutral. A faulty switch could be causing an intermittent issue. (Less likely given the recent transmission replacement but worth a quick check).
Troubleshooting Steps:
1. Check Battery Connections: Make absolutely sure the battery terminals are clean, tight, and corrosion-free. Use a wire brush and battery terminal cleaner if necessary.
2. Listen Carefully During Cranking: When you turn the key, listen closely. Does the starter make a clicking sound (solenoid problem), a grinding sound (starter motor or gear teeth issue), or nothing at all (bad connection)?
3. Tap the Starter: (Use caution!) Gently tap the starter motor with a hammer or wrench handle while someone else tries to crank the engine. This sometimes dislodges a sticking solenoid or other internal component. Only attempt this if you are comfortable working with car components.
4. Test the Starter Solenoid: This usually requires a multimeter to test the voltage and continuity of the solenoid. This is more advanced troubleshooting and requires some electrical knowledge.
5. Check the Neutral Safety Switch (Automatic): Make sure the gear selector is firmly in Park or Neutral when attempting to start. If you're comfortable, you might check the switch itself for proper operation, but this can be tricky.
6. Have it Professionally Diagnosed: If you're not comfortable performing these checks, take it to a qualified mechanic. They have the tools and expertise to properly diagnose the problem.
It's important to address this issue quickly. Continuing to crank the engine when the starter is struggling can damage the battery, starter motor, or solenoid further.
