Technical 15 www.aftermarketonline.net MAY 2026 network, you’d typically see around 2.6V on CAN high and about 2.4V on CAN low with the ignition switched on. However, these values may vary depending on the number of modules and network activity. If the voltages on both CAN high and CAN low are the same, it could indicate a short circuit (which should have been confirmed by your resistance check). If both voltages are at 0V, it might suggest a short to ground. If the voltages don’t look right, you could be dealing with an open circuit or a resistive short circuit. By using the multimeter for these checks, you can quickly identify basic issues such as open circuits, shorts, or abnormal resistances. Oscilloscope diagnosis When you’ve confirmed a network issue and the basics are covered, it’s time to bring out the oscilloscope. An oscilloscope provides a more in-depth analysis of the CAN Bus signals. Here’s what it helps you achieve: O Visualising CAN Bus signals: CAN Bus communication involves electrical signals transmitted as voltage levels on the CAN high and CAN low wires. An oscilloscope allows you to visually represent these voltage signals over time, which provides a clear and detailed view of how data is being transmitted and received on the network. O Identification of faults: An oscilloscope can help you spot anomalies in the CAN Bus signals. It can reveal issues like short circuits, open circuits, voltage spikes, or noise in the network. By examining the waveform, you can identify irregularities which are essential for troubleshooting network issues. O Detection of intermittent faults: Many CAN Bus problems are intermittent, occurring sporadically. The oscilloscope is invaluable for spotting these and helping to pinpoint the root causes. O Resistive fault detection: Sometimes, issues are related to resistive faults, such as high resistance in connectors or wires. An oscilloscope can reveal voltage drops or fluctuations that may indicate resistive problems in the network. O Differentiating high-speed and lowspeed networks: CAN Bus networks can operate at different speeds. An oscilloscope enables you to distinguish between high-speed and low-speed networks by analysing the waveform characteristics. This information is vital for diagnosing the correct part of the network. An oscilloscope is a powerful diagnostic tool for CAN Bus issues, offering real-time visibility into the network’s electrical signals. It helps you identify problems, locate faults, and ensure that the CAN Bus communication adheres to the required standards. Find and isolate CAN Bus faults Diagnosing a network issue is a process of elimination. Start by revisiting any available evidence, such as previous repair history, accident damage, or other work on the vehicle. This information can provide valuable clues for where to begin the diagnosis. If no specific leads are available, you may have to methodically test the network from one end of the car to the other, prioritising the easiest access points. The first step in the diagnostic process is to individually disconnect modules from the CAN bus network. This straightforward procedure can help identify if a specific module is responsible for the issue. It’s a relatively simple test, though some modules might be challenging to access. If the problem persists even after disconnecting modules, it indicates a problem with the wiring. The next step involves locating connectors in the wiring loom, ideally a midpoint in the network, and disconnecting them to determine if the fault lies on one side of the car or the other. In cases where there aren’t any connectors, you might need to trace, cut, and repair wires. Some vehicles use splice points and non-standard joints that can be challenging to locate, so having the workshop data and wiring diagrams available is very important. Sometimes the most complex issues have surprisingly simple solutions. Always start by checking the basics, like fuses and connectors, as these can often be the source of CAN Bus problems. And don’t forget to document your findings, as this can help you track down and resolve issues more efficiently. www.mechanicmindset.com Understanding the network map is essential for CAN bus diagnostics. Always start by checking the basics
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