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Using D-Shift with an OBD Splitter / Y-Cable

We’ve designed the D-Shift Sequential Shift Light to operate as passively as practical, and with smart active / passive OBD functionality, to maximize compatibility when you are using an OBD splitter or y-cable with another OBD device. How well that works will depend somewhat on the other OBD device that’s in use and what it’s doing.

For example, if you also have an OBD dongle, such as our DauntlessOBD or another, you might want to use a track day app or a dashboard gauges app while driving on the track and also using your shift light.

First, many mid 2000s to late 2010 cars often have manufacturer CAN data visible via the OBD port that we know how to decode to get the RPM reading, which allows us to operate entirely passively and eliminate our need to send OBD requests at all. That’s our best option when available, as it gets us fast data with minimal lag, and does not impact any other OBD devices you may be using. Newer vehicles, and all VW/Audi/Porsche, tend to have a gateway that excludes this data from being visible to us via the port (although it can usually be obtained via a Direct Wire installation). When this manufacturer CAN data is not available or understood, we automatically fall back to using OBD requests to get the RPM reading.

When we’re the only device sending OBD requests, this typically works very well. But when there’s another OBD device in use (eg when using an OBD splitter or Y-cable), there is a potential for interference, and we’ve developed some logic to help with that. If the other device is not actively talking to OBD modules, then we’ll operate as normal. When we do detect that another device is talking to OBD modules, then our default Auto Passive Mode will make us go silent to avoid interfering until a little while after we stop detecting those communications.

In that case, we would be passively observing the OBD data that the other device is requesting, and getting our RPM reading by decoding the OBD responses containing RPM data. The catch here is that the other device needs to be actively requesting RPM data, doing it in a standardized OBD way, and doing it as often as possible. Our shift light performance would be dependent on what that other OBD device is doing. Typically, we’d want the RPM data to be requested at least 5 times a second, but preferably closer to 10 for best performance.

We have found that many OBD dongles for your phone are often not very fast, especially the cheap ones that have flooded that market, and would of course recommend our own DauntlessOBD, which was designed with performance in mind.

The D-Shift mobile app also gives you options to disable OBD Queries entirely (forces passive mode), and even to disable Auto Passive Mode (forces active mode).