1. Neutral Safety Switch (NSS): This is the most common cause. The NSS prevents the engine from starting unless the transmission is in Park or Neutral. A faulty NSS might not be properly registering the reverse position, causing the engine to shut down as a safety precaution.
* Troubleshooting: Inspect the NSS for damage or corrosion. Test its continuity using a multimeter in different gear positions. A simple test involves trying to start the engine with the key while moving the shifter through the gears – if it only starts in Park and Neutral, the NSS is likely the problem. Replacement is usually straightforward.
2. Transmission Range Sensor (TRS): Similar in function to the NSS, but the TRS provides the transmission's position to the PCM (Powertrain Control Module). A faulty TRS can also lead to the engine shutting down in reverse. This is often found within the transmission itself and requires more specialized knowledge and tools to replace.
* Troubleshooting: Requires advanced diagnostics, often with a scan tool to read codes. A mechanic might be necessary for diagnosis and repair.
3. Wiring Issues: Damaged or corroded wiring between the NSS/TRS, the PCM, and the ignition system can cause intermittent problems, including shutdown in reverse.
* Troubleshooting: Visually inspect all wiring related to the transmission and ignition for fraying, corrosion, or loose connections. Pay close attention to the connectors at the NSS/TRS and PCM.
4. Low Voltage/Alternator Problems: While less likely to be *specific* to reverse, a weak alternator or other low voltage condition can cause the engine to die under stress, and putting the car into reverse adds a significant load.
* Troubleshooting: Check the battery voltage, and have the alternator tested to ensure it's charging properly.
5. Crankshaft Position Sensor (CKP Sensor) or other engine sensors: Although less likely, a failing CKP sensor (or other critical engine sensors) could be causing the problem. A malfunctioning sensor might result in the engine losing its signal while the added load of the transmission in reverse causes it to shut down.
* Troubleshooting: Requires a scan tool to check for sensor codes.
6. Transmission Problems (rare): In some rare instances, a serious internal transmission problem could be causing the issue, though this is less likely unless accompanied by other symptoms like slipping gears or unusual noises.
Troubleshooting Steps (in order of likelihood):
1. Check the Neutral Safety Switch: This is the easiest and most likely solution.
2. Inspect wiring: Look for any visible damage or corrosion.
3. Scan for codes: Use an OBD-II scanner to retrieve any diagnostic trouble codes (DTCs).
4. Test the alternator: Check for proper charging.
5. Consult a mechanic: If you're not comfortable with auto repair, take it to a qualified mechanic for diagnosis and repair. They have the tools and expertise to diagnose more complex issues.
Remember safety first! Work on the car in a safe, well-ventilated area, and disconnect the negative battery terminal before doing any electrical work.
