Xref: utzoo sci.electronics:19511 rec.autos.tech:23515 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!rphroy!albert.cs.gmr.com!rhaar From: rhaar@albert.cs.gmr.com (Robert L. Haar CS50) Newsgroups: sci.electronics,rec.autos.tech Subject: Re: Hacking Car ECUs Message-ID: <51335@rphroy.UUCP> Date: 22 Apr 91 14:23:32 GMT References: <47590@ut-emx.uucp> <1991Apr14.224844.3126@coral.bucknell.edu> <02~_0R|@warwick.ac.uk> <1991Apr22.131521.2622@ux1.cso.uiuc.edu> Sender: news@rphroy.UUCP Reply-To: rhaar@albert.cs.gmr.com (Robert L. Haar CS50) Followup-To: sci.electronics Lines: 83 Nntp-Posting-Host: albert.cs.gmr.com In article <1991Apr22.131521.2622@ux1.cso.uiuc.edu>, tmkk@uiuc.edu (Scott Coleman) writes: |> |> In article <47590@ut-emx.uucp> lusky@ccwf.cc.utexas.edu (Jonathan R. Lusky) writes: |> > All of the programmable ECM's I've seen have an rs-232 port and are intended |> >to be used with a pc-compatible laptop. |> |> That's interesting - does the same hold true for the computers found in |> most cars these days, or are there general exceptions (i.e. Fords have the |> RS232 port, GM cars don't)? In general, the answer is no. Many original equipment engine controllers have serial ports for diagnostics, but, as far as I know, none are RS232. And they won't do what you want anyway, since they don't allow modifying the code - that is in ROM. A couple of related notes: It is not terribly hard to get better performance (at least in some limited operating range), but the ususal tradeoff is much higher emissions. For this reason, both the EPA and California's ARB are likely to crack down on modified ECM's and will require vehicle manufacturers to take steps to prevent "tampering" with the ECM software some time in the future. (note - ECM is GM talk fro engine control module. Other companies use names like ECU.) The diagnostic datalink (car talk for serial communications line) in most cars uses proprietary protocols and the message formats etc. can vary from one year or car line to another. Many of these are widely known, but may still be considered proprietary information by the manufacturers. Many vehicle diagnostic tool vendors sell equipment called scan tools that plug into the diagnostic datalink and monitor or interrogate the ECM. Even Sears sells them. Some of the more sophisticated ones are PC based. The Society of Automotive Engineers (SAE) has been working for several years on standardizing communications between vehicle modules and with off-board test/diagnostic equipment. One particular effort is called Class B communications. This is aimed at medium speed communications between micro-based modules and includes communications with external equipment such as service diagnostic and manufacturers test equipment. This protocol is maturing well and receiving good acceptance within the industry. It is in SAE document J1850, and is often called the J1850 datalink. J1850 is nothing like RS232. It is a CSMA/CD protocol with non-destructive, bitwise contention that can operate at 10K bps (single wire) or 40K bps (dual wire). C.A.R.B. is writing J1850 in regulations, requiring its use for emissions testing starting in 1995. EPA is likely to fool suit. If there is sufficient interest, I can put together some articles on these communcations protocols. Let me know. Most of the traffic on this group has been more like "which tires should I use" or "how do I know if my brakes are worn out?" These are valid topics, but I am not sure that there are enough interest people to justify my time in writing about more narrow-interest topics. Bob Haar InterNet : rhaar@gmr.com Computer Science Dept., G.M. Research Laboratories DISCLAIMER: Unless indicated otherwise, everything in this note is personal opinion, not an official statement of General Motors Corp.