![]() ![]() You have no problem connecting everything to a good chassis ground. Now in the real world and especially on cars with little electronics such as your Mondeo you usually find that signal and chassis ground are just connected directly together somewhere in the loom.ĬAN bus data is resilient enough to use chassis ground as a reference. This is because you cannot guarantee it is designed to carry significant current. Only use signal ground as a reference when monitoring data, for sensors or diagnostics. So Signal ground and chassis ground always end up connected to the battery negative terminal but the signal ground is just isolated from any noise. Usually signal ground comes from the Engine ECU, diagnostic gateway or nearest ecu/module, signal ground always ends up to ground through either a cleverly designed ground plain in the ECU/Module or through a number of 0Ω resistors or connected at a point far away from any noise. Signal Ground Pin 5: Is designed to provide a 'clean' ground isolated from any noise from devices such as radios, alternators and poorly designed switching regulators.Chassis Ground Pin 4: Is exactly that, connected directly to the chassis or battery negative terminal.The difference between chassis and signal ground is: You are over thinking things, just connect your devices (OBD & Pi) to a good chassis ground: I am going to remove that connector and connect the pins I need to the car via the Quadlock connector. The adapter is connected to the computer via USB. The one I mean is the "in" connector to an adapter for interpreting the bus computationally. More clarification: the car has an OBD-II port under the steering wheel. I find it hard to believe they are just the same. Since I only have one "ground" on the Quadlock, which I assume is battery minus, connected to the chassis, what should I do?īoth 4 & 5 to ground or ignore OBD-II pin 5?Ĭlarification: I am not going to use the car OBD-II port, only the Quadlock connector.Įdit: what I am really wondering is why the OBD-II standard has both chassis and signal ground. I think I understand linguistically what that means, but am not sure why you need both. On 4 it says "chassis ground" and on 5 "signal ground". The Quadlock connector to the stereo apparently includes CAN bus, so I am thinking I will get a USB OBD-II adapter and just solder the relevant pins. Am planning to install a carputer (Raspberry Pi) in a 2005 Ford Mondeo, replacing the car stereo. ![]()
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