Suzuki ECU Diagnostics Explained

Updated 10th September 2013


Suzuki (and Geo badged Suzuki) ECU diagnostics can be categorised into two very broad types, usually refered to as 'OBD1' and 'OBD2'. Prior to the adoption of OBD2 some countries had a mandatory requirement for On Board Diagnostics, others didn't. Most manufacturers did fit diagnostic interfaces and these were usually proprietary. The majority of Suzuki ECUs from 1991 onwards were fitted with a diagnostic link, a notable exception being the Swift GTi models.

The terms 'OBD1' and 'OBD2' are actually very specific to the US but have achieved common usage worldwide. In the US OBD2 was mandated from 1996 onwards, in Europe legislation required the adoption of EOBD (mostly compatible with OBD2) from 2001 for new petrol engined passenger vehicles through to 2004 for existing models of diesel engined passenger vehicles. Japan adopted EOBD in 2004, Australia adopted EOBD in 2006 and India is currently scheduled to adopt it in 2013. Of course manufacturers were free to adopt OBD2 or EOBD before the mandated dates so legislation dates only mean that vehicles introduced after those dates will meet the relevant specification, before those dates they may be OBD2, EOBD or proprietary. The primary interface on Suzuki ECUs is a proprietary format (generally still referred to as OBD1) and where an OBD2 or EOBD interface is also fitted, to meet legislative requirement, it is limited to the legal minimum. The official, and hugely expensive, factory scan tools, the Tech1, Tech2 and SDT use this propritary/OBD1 interface. The Suzuki specifications have not been made public but are available to aftermarket scan tool manufacturers with an annual licence fee being charged. OBD1 on OBD2 ECUs


The Check Engine Light Method
The most basic form of diagnostic interface fitted to a Suzuki flashes fault codes on the Check Engine Light when the interface is activated. Activating the interface requires the insertion of a jumper in the monitor coupler or the insertion of a fuse in the 'Diag' slot in the fuse box. The later method is mainly used on earlier models. The ECU flags fault codes mainly in response to gross errors, ie sensors outputs at supply voltage or grounded. The fault codes cover only emissions related performance and only current faults can be displayed.

The Check Engine Light method is covered in more detail here

The Serial Data Link (SDL)
From 1991 onwards the majority of Suzuki ECUs have a serial link that can communicate with a hand held scanner or a diagnostic interface. The Serial Data Link allows live data to be examined, current and historic fault codes to be examined and various actuators such as the EGR to be remotely operated for test purposes. From 1991 until approx. 2001 in OBD1 markets a wholely proprietary Suzuki interface was used, originally using a 12-pin ALDL type connector and then from 1996 onwards a 16-pin J1962 (OBD2) connector. It should be noted that the wiring to the ALDL connector was not the same as used by GM models; the serial link was wired to pin 9 on the J1962 connector which the specification reserves for manufacturer's assignment. The RhinoPower SDL interface is compatible with this protocol.

The SDL is covered in more detail

From some time around 2001 Suzuki started to use a different proprietary protocol for their factory scan tools, they call this protocol SDL/KWP. SDL/KWP was implemented worldwide and for markets where OBD2 was not mandated this was the only protocol available. OBD2/EOBD models have SDL/KWP as the primary interface and OBD2/EOBD as the 'public' interface'. As the name suggests this protocol uses the KWP2000 protocol and uses pin 7 as specified by the J1962 specification, however there is no support for the OBD2 modes specified by J1979. Although the ECU will correctly respond to an 'OBD2' request with a not supported message many OBD2 scan tools incorrectly report 'cannot connect' or 'no data' rather than 'not supported'. If an ELM tool is available then a terminal emulator programme such as Hyperterminal can be used to check the response to a Mode 1, PID0 (0100) request, a 0x7F response means that it is an OBD1 ECU. RhinoPower Ltd is working on a scan tool and software that will be compatible with KWP/SDL and OBD2 protocols using pin 7.
The Factory Service Manual for some models states the protocol to be ISO9141-2, this is because KWP2000 is a software protocol, it uses the ISO9141-2 hardware interface.

Other Protocols
Some Suzukis that use an engine and electronics bought in from another supplier may use a protocol proprietary to the engine supplier. Some Suzuki models with FIAT diesel engines are known to use a FIAT version of the KWP specification.


The use of the expression 'OBD2 specification' is commonplace but it must be noted that 'OBD2' refers to a specific piece of US legislation and that there are a large number of different specifications that are implemented by thge OBD2 legislation. The original intention to have a common protocol was a dismal failure and the OBD2 legislation allowed several different protocols to be used with KWP2000 being added later. EOBD is to all intents and purposes the original OBD2 protocols plus KWP2000 so I will just call everything OBD2. In 2001 an international standard for on board diagnostics, ISO15031, was introduced and most markets are now adopting CANBus as the only allowed hardware protocol so some standardisation is finally happening. OBD2 Suzuki ECUs generally use ISO9141-2 up to 2001 and KWP2000 from 2001 until the introduction of CANbus from around 2006.
Nearly all of these Suzuki ECUs also have a proprietary interface/OBD1 interface that gives extended diagnostic capabilities and for non-engine related ECUs such as airbags and ABS. To access all functions a professional scan tool is required, however for most emission related functions a generic tool such as the ELMScan will suffice.
Information on the specifics of the OBD2 protocols is widely available on many sites on the internet however the specifications were originally only available for a fee and hence a lot of the information published is based on hearsay. Older copies of the specifications have now been released by the US government. As an automotive designer I do have access to the latest specs. but the terms of the licence prevent me from reproducing them.

The are available through the forum and have some schematics, code disassemblies and other specific details which can be of use when fault finding at PCB level. I also have a good deal of information about the various ICs and other components that can be very difficult to find. A lot of this is not yet published so feel free to ask on the . Please note that the forum is not there to assist with general running problems, a Factory Service Manual is the best source for that sort of information.