Assembly Line Diagnostic Link or ALDL is a proprietary on-board diagnostics system. Multiple scanner software programs are available. 'Engh Motors - Makers of GMTDScan, the PC OBDI/ALDL scan tools for 1994-1995 GM 6.5TD trucks'. 3 Things Needed There are basically 3 things you need to record diagnostic data from a GM based On Board Diagnostic 1 ( OBD1 ) system on your 1982 - 1995 era car. 1 - A PC computer, preferably a laptop, to collect, log, and analyze the OBD data. 2 - An ALDL cable to interface your PC computer to the ALDL OBDI diagnostic port on your car. 3 - A software program running on your PC to capture the. GM 8192/160 Baud ALDL Interface GM 8192/160 Baud ALDL Interface NEW! We'll soon describe an alternative, possibly cheaper, two transistor circuit. We'll have 160 and 8192 baud software soon too (but see below for a range of free software available now). • A simple hardware interface between GM's 5 Volt and a PC's serial port is described here. This same hardware can be used for earlier 5 Volt and 12 Volt streams. But use if you only need to look at ALDL data. ALDL 8192 baud Hardware There have been a number of designs published (none by GM) to enable the GM proprietory ALDL data stream to be tapped into. Our design uses a MAX232 (or MAX233) because this is the simplest way to do it. We also avoid using a separate power supply by powering the MAX chip from the PC's serial port (DTR and RTS signals must be set to +ve). This circuit can also be used to read older ECU's 160 baud ALDL signals. Here's our circuit using the MAX232 (or MAX232A). Vehicle signals are on the left, PC signals on the right, with DB9 (and DB25 in brackets) pin assignments shown (pin N on DB9 is N/9, etc.). Note that the 3.3 uF capacitors (C1-C4) may be reduced to 1 uF if these are readily at hand, or to 0.1 uF if you use the MAX232 A. If you use a MAX233, which has a different pinout to the MAX232, you don't need to use any of the capacitors C1-C4, but the regulator still requires C5 and C6. More information is available, or you can download the data sheets for their. As well, get the from Natsemi, and the from Fairchild. Early ECUs produced a fixed 8192 ALDL data stream when the user placed a 10k ohm resistor between ALDL connector pins A and B. Later ECUs added internal receive circuitry (the chip). Nonton drakorindo doctors. For enhanced capabilities, and their firmware was upgraded too. Software can be used to enable the 8192 ALDL data stream from these later ECUs. ![]() The 8192 baud Rx and Tx data to/from the PC is combined with a diode and resistor (D3, R1) before being sent to the ECU. The 160 baud data is sent to the PC and appears as a toggling CTS signal. Thus no mechanical switching is required to select either 160 or 8192 baud data streams. The diagnostic sense resistor R3 may not be required for later ECUs where software controls the ALDL data. The power supply uses two signal lines (RTS and DTR) from the PC to provide a positive voltage for the MAX chip. The two diodes (D1 and D2) are used to ensure power is available even if only one signal line is positive. Capacitor C6 ensures the low power 78L05 regulator is stable in operation. Capacitor C5 provides decoupling and filtering from the PC. C1 through C4 are the charge pump and inverter capacitors - their orientation (assuming you use tantalum types) should be double checked. OBD Diagnostics Products: GM OBD1 Cables Low Cost ALDL OBD1 Cables - $59.95 12-Pin Version 16-Pin Version 3 Things Needed There are basically 3 things you need to record diagnostic data from a GM based On Board Diagnostic 1 ( OBD1 ) system on your 1982 - 1995 era car. 1 - A PC computer, preferably a laptop, to collect, log, and analyze the OBD data. 2 - An ALDL cable to interface your PC computer to the ALDL OBDI diagnostic port on your car. 3 - A software program running on your PC to capture the OBD data. Why This Setup? What is the reason for having the above setup for yourself? Mainly, you now have a powerful tool to analyze your cars OBD data yourself, better even than the specialized scanning tools only dealerships and big shops had in the distant past. With your own setup, if your Service Engine Soon ( SES ) light comes on you can look at detailed OBD data for yourself to see what trouble codes have been set and the conditions they were set under, possibly saving you money in repair costs by knowing what is or isn't wrong with your car. For many, it is quite interesting to be able to see your car's sensor systems working in real time, and even having the potential to upgrade performance through PROM reprogramming of your cars ECM/PCM (not for the beginner). The ALDL Cable Let's look at the ALDL (Assembly Line Diagnostic Link) OBD1 interface cable first, since we sell low cost ALDL OBD1 interface cables.
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