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Trigger your car’s self-diagnostic fault codes SELF DIAGNOSTICS PLUG by Julian Edgar F or many years cars have logged any faults that occur in their engine management system. The most advanced systems record not only the fault, but also engine operating conditions at the time the fault occurred. These systems normally need a dedicated data reader (eg a manufacturer’s own service tool) to read them. But nearly every car has a simpler way of accessing these codes. By linking two pins in the diagnostics plug, most cars can be made to flash their diagnostic codes on the dashboard Check Engine light. For example, two short flashes followed by four longer flashes might indicate the fault code number ‘24’, and finding out what ‘24’ means is as simple as looking up a service manual. Even basic manuals have these codes listed. Cars sold or built in the United States after January 1, 1996, use what’s called an OBDII diagnostics system. 14  Silicon Chip ‘OBD’ stands for Onboard Diagnostics and represents a standard that allows certain engine data to be downloaded, including fault codes. (Well it’s kind of a standard – see the ‘OBD – Oh Bloody Difficult?’ breakout box.) The influence of the huge US market is such that many cars sold in other countries also have an OBDII socket The plug inserted into an OBDII port. In this car the socket is located under the steering column. www.siliconchip.com.au The OBDII plug comes with the pins and shell separate. In this application only two pins need to be used. Here the wire link between the two pins can be clearly seen. The connections to the pins can be made by soldering or crimping The plug inserted into an OBDII port. In this car the socket is located under the steering column. fitted. Many of the pins in the OBDII socket aren’t used by the standard, so most manufacturers also mount in the same plug the pins that can be bridged to trigger the trouble codes. So, easy, huh? Just dive under the dash, find the OBDII plug, check in a workshop manual which pins need to be bridged and….. er…. Yes, it’s not much fun trying to insert the end of an unbent paper clip into the socket pins while lying upside-down under the dash, is it? In fact, it would be damn easy to bridge the wrong pins and potentially cause all sorts of catastrophic damage… And that’s where this very simple idea comes in. Jaycar Electronics has recently started selling an OBDII compatible plug. Which means that rather than fiddling with a wire link, all that you need to do is permanently wire the connection in place inside the plug, and when you want to trigger the fault codes, simply plug it into the socket. As mentioned, the last one is pretty easy – even basic workshop manuals list the fault codes, and the factory workshop manual will normally go into pages of detail on each code. Good factory workshop manuals will also help you out with the second requirement – knowing which pins to bridge to trigger the self-diagnostics. These manuals are available at the Whoa! But let’s take a step back. For this system of easily triggering fault codes to work on your car you need three things: • A car with on an OBDII socket • Access to the information about which pins need to be connected to trigger the fault codes • Information about what those fault codes mean The OBDII connector is a 16-pin design which uses these pin placements. www.siliconchip.com.au “OBD” – Oh Bloody Difficult? Of course the primary function of the OBDII socket is to allow the transfer of data. In fact, commercially available readers exist that can display live engine operating information – in addition to fault codes – on a Windows CE or Palm handheld, or a PC. We’ve also seen kits for the adaptors that will take the data out of the OBDII port and allow you to display it in all kinds of great ways. So why aren’t we covering just such a project here? There are two main reasons. Firstly, there is not just one OBDII standard, but rather there are four different standards. Many of the readers can work with only one standard, although it must be said, just a few will cope with all four. But for us here in Australia, the major difficulty is that many of our cars don’t have OBDII compatibility. We can just imagine how happy you’d all be if we covered a kit and when you built it, you found it wouldn’t work with your car, despite the fact that it had an OBDII port. And despite the fact, even, that it had ‘OBDII’ written on it and it said in the manual that it was OBDII compatible... It is a fact of life that many of the cars sold in Australia aren’t fully compatible with the OBDII standard. It’s not required that cars sold here are OBDII compliant and many manufacturers don’t bother doing so. In the case of the author’s 1998 Lexus LS400, for example, despite the factory workshop manual clearly claiming that the car was OBDII compliant, and despite the fact that it had OBDII written on the cover of the (OBDII) socket, a commercial OBDII data reader fails to work with the car. Why? The software inside the ECU is not compatible with OBDII! In fact, in our experience there is a range of Australian-delivered cars that transmit at least some OBDII data (late model Holden, Subaru, Mazda, Honda, Porsche) and also a range of cars that do not (Falcon, Peugeot, Lexus). That’s the total sample that so far we’ve looked at – many more cars will be in one category or the other. There is simply no way of telling whether the car is OBDII compliant without plugging in a data reader and seeing if it works. That Mazda supports it and the Ford Falcon does not is even more confusing, since the companies now share much of their engine management technology. Note also that service departments have no idea which of their cars are OBDII compliant and which aren’t. They just plug in their factory service tool and away they go. In the future it may be that more cars in Australia will become OBDII compliant (although there is a mooted OBDIII standard which might throw another spanner in the works). If OBDII – or a similar standard – is mandated in Australia, we will then be very interested in doing a data reader project. Because when the OBDII data stream is actually working, it’s fascinating stuff indeed. December 2003  15 ing wire between them and inserting them into the right holes from the rear of the plug (the pins will click into place only if inserted with the correct orientation). Make sure that you view the plug from the rear when selecting the correct pins, as all workshop manuals show the view looking into the socket! Using It In most cars the Check Engine light will flash out the fault codes. However, in the case of the Lexus shown here, the actual fault code number is displayed. service departments of car dealers and also, in many cases, in the libraries at TAFE colleges where automotives is taught. But the first step is to see if your car has an OBDII socket. As mentioned, that will only be the case if the car was made after January 1, 1996. The socket is legally required to be located inside the cabin, and must be able to be accessed without tools. (In practical terms, a small screwdriver may be needed to lift an interior trim panel.) Start off by looking under the dash, behind the ashtray, under the glovebox, under the trim panel beneath the handbrake and in similar places. The 16-pin socket has a characteristic shape (wider at the top than the bottom) and may be protected by a push-on cover. Once you’ve found it, see if you can get the info on the pins that need to be bridged – perhaps start with the service department of the local new car dealer. Building It As one of the simplest projects we’ve ever covered, this part shouldn’t take you long. The Jaycar plug (PP0720) is provided with the pins and plug body - you need to insert the pins into the plug to form the assembled item. To put the plug together it’s just a case of separating two pins from the strip to which they’re tied, soldering or crimping a short insulated bridg- In the case of the author’s Lexus LS400, the workshop manual indicates that fault code triggering will occur if pins 13 and 4 are bridged. In this car the codes are displayed in numeric form on the multifunction LCD dash display – no flashes need to be counted. So after the plug was wired it was just a case of plugging it into the OBDII socket and then following the workshop manual’s instructions to display the fault codes on the dashboard display. After you’ve finished doing the fault diagnosis, it’s easy to keep the plug in the glovebox. SC The 1999 Hyundai Accent Don’t think that you’ll find an OBDII connector in just expensive cars. The 1999 Hyundai Accent has an OBDII socket with its pins having the following functions: Pin 1 – TCM Pin 4 – Ground Pin 7 – Engine Pin 8 – ABS Pin 12 – Airbag Pin 14 – Vehicle Speed Pin 15 – L-wire Pin 16 – Battery + This is straight out of the workshop manual – no, we don’t know what ‘TCM’ is either. But we do know from the manual that triggering the fault codes requires these steps: 16  Silicon Chip (1). Turn on ignition (do not start car) (2). Ground the L-wire in the data link connector for 2.5 – 7 seconds (3). If no fault is present, ‘4444’ will be flashed on the Malfunction Indicator Light (MIL is another name for Check Engine Light) (4). Each codes repeats until the L-wire is again grounded, whereupon the next code appears (5). ‘3333’ indicates the end of code outputs So for the Excel, Pin 15 needs to be wired to Pin 4 in the OBD plug. Then just insert the plug for about five seconds to start the fault diagnosis process, with up to 21 fault codes then available. Auterra (www.auterraweb.com) make an excellent general-purpose OBDII reader that works with Palm OS devices. Here the ignition timing advance and airflow meter mass flow are being read live from a Holden Astra Turbo on a Treo 270 smartphone. However, many Australian-delivered cars are not OBDII compatible, despite often having an OBDII port. www.siliconchip.com.au