Mercedes-Benz B250 Electric Won’t Start or Drive

Electric Mercedes-Benz vehicles such as B250e may show a malfunction visit workshop error message on the dashboard and other messages such as “Stop Switch Engine Off.” In most cases, the vehicle may power up but not drive. It is important to read the fault codes with a full system scanner. A common fault code is P1C0300 – a vehicle side isolation fault in the high voltage onboard electrical system may be present if you scan the vehicle with the YOUCANIC full system scanner.

When the hybrid vehicle detects an isolation breakdown between the high-voltage battery and the 12-volt system, it triggers an error code. This can occur due to various factors, such as ruptured or leaking cells, damaged high-voltage cabling insulation that has come into contact with low-voltage systems, condensation, or non-isolated equipment. It may also be due to an intentionally non-isolated design. It’s important to note that this error code can indicate an unsafe condition in the battery pack. While investigating the error, care must be taken to avoid the risk of short circuits and personal injury from electric shock. Even a simple touch of a cell could result in an electric shock. While this error typically indicates a genuine issue, there are also some situations where a false positive can occur.

Symptoms

• The vehicle won’t start or drive.
• Visit Workshop Message on Instrument Cluster
• Stop Switch Engine Off error
• Without restarting, consult the workshop.
• The vehicle won’t go into Drive

Causes

• Weak 12-volt battery
• Defective DC/DC converter
• Damaged high voltage (orange) cable insulation
• Defective hybrid battery
• Faulty battery heater

Troubleshooting

Step 1: A full system scan can provide a comprehensive overview of any issues or malfunctions within the vehicle’s systems and subsystems. This can include faults in the engine, transmission, brake system, airbag system, or any other electronic control unit. Scanning the vehicle’s systems can identify and address any hidden issues before they cause major problems or failures.

It’s important to note that running a full system scan requires a compatible diagnostic tool or scanner specifically designed to work with the make and model of the vehicle in question. These tools are designed to communicate with the vehicle’s onboard diagnostic system (OBD) and retrieve any codes or information that may be stored within the system. Once the scan is complete, the diagnostic tool or scanner will display any fault codes that have been identified. These codes can pinpoint the root cause of the issue, making it easier for mechanics or technicians to make the necessary repairs.

Step 2: To begin troubleshooting an isolation fault, the first step is to determine whether the system is intended to be isolated and whether other isolation detection circuits are connected simultaneously. If the overall system is intentionally designed to be non-isolated, then the isolation fault detection should be disabled. It’s also important to note that other isolation fault detection circuits operating on the same battery pack may interfere with each other, potentially leading to false readings. Therefore, checking for any such circuits and disabling them if necessary is crucial to ensure accurate fault detection and resolution.

Step 3: Measure the resistance. Typically good insulation is over 1M ohm, while a reading below 1M ohm may indicate a dead short. It’s important to note that external factors can affect the exact numbers, so some variation is to be expected.

Step 4: If the isolation is found to be degraded only when the system is cold, the cause could be condensation. When cold, water can condense on cables, battery terminals, or other exposed connections, creating a path for current to flow to the chassis or low-voltage system. In addition, conductors and cells may expand and contract with temperature changes, potentially causing them to come into contact with other parts and degrade isolation. Therefore, inspecting all exposed connections and components carefully and addressing any identified issues to restore proper isolation and prevent any safety hazards.

Step 5: If the isolation is found to be degraded according to the shortest wave value, an effective troubleshooting step is to attempt to isolate various systems while monitoring the shortest wave measurement. For example, disconnecting or fully isolating a battery charger from the battery pack may improve the isolation number. If such a system is identified, it’s important to investigate the cause of isolation breakdown or replace the defective system. However, taking appropriate precautions is crucial to prevent personal injury and to short of cells. A cell may be shorted to the chassis, causing it to be electrically ‘hot,’ Simply touching a cell and the chassis may result in electric shock. If safe, disconnect any device with extra capacitance to the ground, such as chargers, inverters, DC/DC converters, or cabling with excessive parasitic capacitance.

Step 6: If the shortest wave measurement continues to show degraded isolation even after performing the above steps, it’s important to investigate isolation faults within the battery pack. Such faults can be caused by various factors, such as leaked electrolytes, liquids shorting to the chassis, battery terminals shorted to the chassis, chafed wiring, conductive debris, or other causes. It’s important to note that inspecting the battery pack can be hazardous, and care must be taken to avoid personal injury and prevent shorting of cells. When inspecting the battery pack, it’s essential to be mindful that a cell may be shorted to the chassis, causing it to become electrically ‘hot.’ Therefore, any work should be carried out cautiously and with the appropriate safety measures.

Conclusion

To diagnose the underlying cause of why an electrical Mercedes-Benz won’t start is to start by reading the fault codes using a full system scanner. Possessing significant troubleshooting skills and expertise is essential, as this diagnostic trouble code can be triggered by various underlying issues that may not be readily apparent. It’s worth noting that if you’ve identified an additional issue that may have contributed to this fault in your vehicle and it’s not listed here, we welcome you to share it in the comments section below. Your input could be helpful to others experiencing similar issues with their vehicle.