Experiencing difficulty starting your Mercedes-Benz Sprinter can be frustrating, especially when diagnostic tools like Xentry point to synchronization faults. This article delves into a common scenario where Sprinter owners face starting problems, often intertwined with error messages related to Xentry connectivity and sensor synchronization, specifically focusing on the CAM (Camshaft Position) and Crank (Crankshaft Position) sensors. We’ll explore potential causes, diagnostic steps, and how to interpret sensor readings to get your Sprinter back on the road.
One frequently reported symptom involves issues with the CAM sensor signal. A technician or DIY mechanic might observe that while the CAM sensor readings appear normal when disconnected, the signal voltage inexplicably drops to zero once the electrical connector is plugged in, before cranking the engine. This behavior can be perplexing. In a properly functioning system, the reference and signal wires of a Hall-effect sensor (like many CAM and Crank sensors) should maintain a voltage, often around 5V, even with the connector plugged in. The signal wire is then modulated, typically pulled low in a square wave pattern (0-5V), as the sensor detects the rotating camshaft or crankshaft during engine operation.
If your Xentry diagnostic system reports a “synchronization faulty” error KOEO (Key On Engine Off), but indicates “synchronization RUNNING, then OK” during cranking, this strongly suggests a problem related to either the CAM or Crank sensor signals, or their interpretation by the Engine Control Unit (ECU). The fact that starting fluid allows the engine to briefly start can be a crucial clue. Starting fluid bypasses the normal fuel injection system. If the engine starts with starting fluid, it indicates that the engine can run, and the issue might be related to fuel delivery or ignition timing, which are often dependent on accurate CAM and Crank sensor signals. These sensors are vital for the ECU to determine engine position and speed, essential for correct fuel injection and ignition timing.
To diagnose a potential CAM sensor issue, especially when observing a voltage drop upon connection, consider these steps:
- Verify Power and Ground: Ensure the sensor is receiving proper power and ground. Use a multimeter to check for 5V reference voltage and a solid ground at the sensor connector with the key ON.
- Inspect Wiring: Carefully examine the wiring harness leading to the CAM sensor for any signs of damage, corrosion, or shorts. A short to ground on the signal wire could explain the voltage drop when connected.
- Sensor Function Test: As demonstrated in many online resources, including videos on testing Hall-effect sensors with a voltmeter, you can simulate sensor operation by passing a metallic object near the sensor head while it’s connected and powered (but removed from its installed position). A properly functioning Hall-effect sensor should switch the signal voltage as it detects the metal. If your CAM sensor behaves as described in the original observation – restoring to 5V when removed and dropping to 0V when metal is brought close – it might indicate the sensor itself is reacting, but something is wrong in its installed environment.
Regarding the Crank sensor, particularly a 2-wire sensor, troubleshooting involves different techniques compared to a 3-wire Hall-effect sensor. Two-wire crank sensors are typically inductive sensors. To test a 2-wire crank sensor with a Digital Multimeter (DMM):
- Resistance Check: Measure the resistance across the two sensor terminals. A healthy inductive sensor should have a specific resistance value within the manufacturer’s specifications. An open circuit or short circuit would indicate a faulty sensor.
- AC Voltage Output (Cranking): While cranking the engine, use the DMM in AC voltage mode to measure the voltage output from the sensor. As the crankshaft rotates, the sensor should generate a small AC voltage signal. No voltage or a very weak signal can indicate a faulty sensor or an issue with the trigger wheel on the crankshaft.
Another point raised in the original observation is the Engine Coolant Temperature (ECT) sensor reading. Xentry specifying a coolant temperature above 60 degrees Celsius for starting, while the actual reading is 31 degrees Celsius, could be significant. While an ECT sensor reading of 85 degrees Celsius later indicates the sensor can reach higher temperatures and might not be completely faulty, an inaccurate cold start reading could contribute to starting issues. The ECU uses ECT sensor data to adjust fuel enrichment during cold starts. If the ECU believes the engine is warmer than it actually is, it might not provide enough fuel for a successful cold start.
In conclusion, troubleshooting Sprinter starting problems often requires a systematic approach. Focusing on Xentry diagnostic codes, sensor signal analysis (especially CAM and Crank sensors), and considering factors like ECT sensor readings are crucial steps. The observation of the CAM sensor signal dropping upon connection is a key symptom that warrants careful investigation of wiring, sensor functionality, and potential mechanical issues within the engine that might be affecting sensor operation. If you’ve exhausted DIY diagnostic steps, seeking professional help from a technician experienced with Mercedes-Benz Sprinter diagnostics and Xentry systems is highly recommended.
