* Faulty Injector: While seemingly counterintuitive (a stuck-open injector usually shows *lower* voltage due to less resistance), a partially shorted injector coil could cause a higher-than-normal voltage reading. The increased resistance from the short might still allow some current flow, but the voltage drop across the partially shorted coil would be less than expected. This is less common than other causes.
* Wiring Harness Issues: A break or short in the wiring leading to the specific injector can cause voltage fluctuations and potentially higher readings. This includes damage to the insulation, corrosion on connectors, or poor connections at the injector itself. Check for broken wires, chafing, or corrosion in the wiring loom near the injector.
* ECU (Engine Control Unit) Problem: A malfunctioning ECU could be sending an incorrect signal to the injector, leading to a persistently high voltage. This is a more serious issue and requires professional diagnosis.
* Fuel Injector Driver Circuit within the ECU: The ECU has a specific circuit dedicated to controlling each injector. A problem within this circuit (e.g., a faulty transistor) might cause one injector to receive an excessively high voltage. This is likely a sophisticated internal ECU issue.
* Ground Issues: A poor ground connection anywhere in the circuit can cause voltage anomalies. The ground connection for the fuel injectors needs to be meticulously checked for corrosion or loose connections.
* Incorrectly Calibrated or Faulty Fuel Pressure Sensor: While not directly causing the high voltage, an inaccurate fuel pressure reading can lead the ECU to compensate by sending a higher voltage to the injector.
Troubleshooting Steps (in order of ease):
1. Visual Inspection: Carefully examine the wiring harness leading to the affected injector. Look for any visible damage, corrosion, or loose connections.
2. Connection Checks: Disconnect and reconnect the injector connector. Clean any corrosion from the connector pins.
3. Voltage Measurement at the Injector Connector: Using a multimeter, measure the voltage at the injector connector *with the ignition on but the engine off*. Compare it to the voltage at other injectors. A significant difference points to a problem with that specific injector or its wiring.
4. Resistance Check (Injector): With the injector connector disconnected, measure the resistance across the injector terminals. This helps determine if the injector coil is shorted or open. Compare the reading to the specifications for that particular injector.
5. Advanced Diagnostics: If the above steps don't reveal the problem, advanced diagnostics with a BMW-specific scan tool are necessary. This will allow you to see live data from the ECU, including injector pulse width and voltage, and potentially pinpoint the fault.
Important Note: Working with automotive electrical systems can be dangerous. If you are not comfortable performing these checks, consult a qualified mechanic or BMW specialist. Incorrect diagnosis and repair attempts can lead to further damage.
