Computerized vehicle failure diagnostics

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Introduction

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Jimnys, as most other vehicles built in the 21st century, have several computers which control or monitor various vehicle's systems (like the engine and engine peripherals, ABS, 4WD, instrument panel, etc.).


As the Jimnys 3 have been in production for 20 years (1998 - 2018), Suzuki used a few different computers as well as communication protocols and interfaces throughout the years.

The details about communication protocol(s) with computer(s) in Jimnys 4 are currently unknown - add them here if you know!

Whenever a "sophisticated" issue with the vehicle occurs, using computerized diagnostics to determine the failure code is usually essential to determine the what is actually the problem.


General info on computer diagnostics protocols

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Read this article on general Wikipedia to educate yourself about various computer diagnostics protocols used in the automotive industry.


  • If you are too lazy to educate yourself, you should at least know that there are two main public and manufacturer independent communication standards for vehicle on-board diagnostics - OBD1 and OBD2.
  • OBD1 was used in the 1990s and early 2000s, while OBD2 (slowly) became used in the early to mid 2000s, and is still used today as the predominant public communication standard for computerized vehicle failure diagnostics.


  • In Europe legislation required the presence of EOBD ("European OBD") communication interface (mostly compatible with OBD2) from 2001 for all new petrol engined passenger vehicles and from 2004 for all diesel engined passenger vehicles.
    • Japan adopted EOBD in 2004, Australia adopted EOBD in 2006 and India should have adopted it in 2013 (needs verification).
  • Before those dates, European market (and probably other markets too) did not have any legal requirements regarding computerized vehicle failure diagnostics.
    • Therefore, the situation in these markets in that era varied from one manufacturer to another.
      • Some manufacturers used OBD1, some used OBD2, others used proprietary protocols, or even no vehicle computers at all.


  • A limitation of EOBD/OBD2 is that it is primarily intended for monitoring emissions functions. Only PIDs that are specified by J1979 are permitted. Although the number of PIDs has been greatly increased over the years it is not possible to add additional, important functions, such as Desired Idle or Injector Pulse Width.
  • To provide ‘dealer level’ diagnostics manufacturers add their own ‘proprietary’ diagnostics, for example Suzuki vehicles using KWP2000 use a protocol known as KWP/SDL which utilises Modes 22 and 23 of the KWP2000 specification. Because most diagnostic tools/software only support EOBD/OBD2 mandated protocols a proprietary tool is usually required to access this data.
  • Suzuki vehicles supplied for regions that do not mandate EOBD/OBD2 only implement the more comprehensive ‘proprietary’ interface.

Diagnostics communication protocols in Jimnys

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Overview

  • Before around 2001, Suzuki's proprietary protocol was called SDL (Serial Data Link).
  • Since around 2001, Suzuki uses a new proprietary protocol called SDL/KWP (KWP part stands for KWP2000 technology).
  • The official, and super-uber-duber expensive factory Suzuki diagnostics scan tools (the Tech1, Tech2, SDT, etc.) use one (or both) of these proprietary protocols.
    • The specifications of Suzuki's proprietary protocols of course have not been made public, but are available to aftermarket scan tool manufacturers with an annual license fee being charged.


Basic diagnostics

  • The most basic / crude form of computerized diagnostic fitted to a Suzuki vehicle flashes fault codes (in a quasi "Morse code" style) on the Check Engine Light in the instrument panel when the a certain "physical" input signal (indicating "I want to see trouble codes") to the ECU is given.
    • The input signal is usually given by inserting a fuse in the 'Diag' slot in the fuse box (mainly used on earlier models) or by shorting some pins by on the communications connector.
      • This will probably be the only diagnostic method for you if you have an early Jimny (1998 - cca 2001), or unless you pay more for the factory scan tool than your Jimny is worth.
  • The ECU, when invoked like this, will flag fault codes which are mainly dealing with gross errors.
    • The displayed fault codes are then cycled through showing multiple codes where they have been recorded, include some historic stored codes.
  • This crude diagnostic method works on all Jimnys 3. Someone should try and report if it works on a Jimny 4.


Generic computerized diagnostics

  • A standard cheap computerized diagnostic solution is to use any ELM327-compatible OBD2 vehicle diagnostics protocol reader device together with any of a multitude of generic OBD2 code reading programs (made for Windows, Mac OS, Android, iOS or some other operating system).
  • Beware that this generic hardware + software equipment will provide you only the basic generic OBD2-level access to the vehicle ECU, because of Suzuki's intentional restriction.
    • Read more about this limitation in the previous overview subchapter of this chapter.
    • This essentially means that some errors or engine working parameters might not be presented in proper detail or that some errors and engine working parameters might not be reported at all.
      • A possible example: Where a generic OBD2 protocol would report just a "Glow plug circuit failure" code (so any of the four glow plugs could be defective, or even either of their power supplies could be defective instead), a proper Suzuki equipment would report "Glow plug no. 3 defective" or "Glow plug no. 2 control resistor malfunction".


SZ Viewer program

  • A very smart and philanthropic Russian programmer made a program called SZ Viewer.
    • The program is specifically designed to communicate with computers in Suzuki's vehicles which use Suzuki's proprietary SDL-KWP and SDL-CAN communication protocols.
    • What's even better, it does not require an exotic hardware vehicle diagnostics communication dongle to operate.
      • SZ Viewer requires the use of a (relatively cheap) ELM327 v1.4+ compatible hardware transponder (with Bluetooth or Wi-Fi communication).
    • The program works on Android operating system, and it is normally available from Google Play Store.
  • SZ Viewer is completely free to install and use, but it really deserves some donation to the programmer.


  • In practice, SZ Viewer can read most (and perhaps even all?) Suzuki-specific diagnostic trouble codes from Suzuki vehicles' computers which otherwise require the use of original Suzuki's diagnostic tools.
    • Generic / ordinary hardware and software DTC scan tools can read only the limited/coarse "public" subset of OBD2 trouble codes which Suzuki enabled just to comply with legal requirements (as explained in the previous chapter).
  • If you did not get it yet - this free program + a cheap transponder enable you to have probably around 80% of diagnostic functionality of a super-duper expensive original Suzuki scan tool when diagnosing errors in a Jimny 3.
    • It is not currently known if SZ Viewer works with Jimny 4 - someone should try and report.


The rest of this article is to be written soon ...


References

Part of this article was written based on the sources below:



Page last edited on 11/06/2019 by user Rhinoman