A car scanner (OBD2 scanner) is a useful tool, but it's often not the right first step for a "car won't turn over" issue. When a car "won't turn over," it means the starter motor isn't cranking the engine. This is typically a problem with the starting system—not the engine computer that the scanner reads. Your initial diagnostic steps should focus on the battery, starter, and ignition system.
The most common culprit is a dead or weak battery. Check if your headlights are bright when you turn them on; if they're dim or don't work, the battery is likely the issue. Corroded or loose battery terminals can also prevent a good connection. Next, listen for a click when you turn the key. A single, solid click often points to a faulty starter motor or a poor electrical connection to it. If you hear rapid clicking, that's a classic sign of a weak battery that can't provide enough power to engage the starter.
While an OBD2 scanner won't diagnose a dead battery, it can be helpful in a specific scenario. If the car's security system (immobilizer) has a fault, it can prevent the engine from cranking as an anti-theft measure. The scanner might retrieve a security-related trouble code that points you in the right direction. However, for most no-crank situations, a simple multimeter is a more effective tool for checking battery voltage and electrical connections.
| Common Cause | Symptom | Simple Check | Scanner Helpful? |
|---|
| Dead Battery | Dim lights, rapid clicking | Test headlight brightness | No |
| Faulty Starter Motor | Single loud click, no sound | Tap starter lightly with a tool | No |
| Bad Ignition Switch | No dash lights, no click | Jiggle key in ignition | No |
| Faulty Security System | Security light flashing on dash | Try a spare key | Yes (may show code) |
| Blown Main Fuse | Complete electrical failure | Check fuse box for blown fuses | No |
Start with the basics: check the battery voltage (should be above 12.4 volts), inspect terminals for corrosion, and ensure the car is in "Park" or "Neutral." If those are good, then you can consider if a scanner might reveal an immobilizer code, but mechanical and electrical checks come first.
