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On Board Diagnostics (OBD) ICs

Our "OBD Interpreter" ICs are designed for use with vehicles that use the standard OBDII (On Board Diagnostics) protocols. Most modern vehicles use the CAN (ISO15765-4) protocol, but yours may not. If you are unsure of what protocol your vehicle uses, see the 'obd help' section.

Our ELM327 is the only product that supports all of the standard OBDII protocols, but you may not need that many. To help you decide which chip to buy, we offer the following chart:

  the ELM320 the ELM322 the ELM323 the ELM325 the ELM327 the ELM328 the ELM329
  SAE J1850-PWM X       X    
  SAE J1850-VPW   X     X    
  ISO 9141-2     X   X    
  ISO 14230-4 (slow)     X   X    
  ISO 14230-4 (fast)     X   X    
  ISO 15765-4 (CAN)         X   X
  SAE J2411 (SWCAN)         X   X
  KW1281 (SAE J2818)              
  SAE J1939 (250kbps)          X   X
  SAE J1939 (500kbps)         X   X
  SAE J1708 (J1587)       X      
  SAE J1708 (J1922)       X      

Note that we have also included a couple of non-OBDII protocols that we are often asked about.

OBD Interpreters

ELM320 - OBD (PWM) to RS232 Interpreter (v2.0)

The ELM320 allows you to talk to your 41.6KHz J1850 PWM protocol vehicle through a standard RS232 serial connection, using only simple ASCII commands. This data protocol was commonly used in many Ford Motor Company vehicles (but is now being replaced by CAN).

The data sheet shows how to connect this IC into a low cost circuit which provides all the functionality of a scan tool that cost considerably more. Once built, a simple terminal application, and perhaps a USB to RS232 converter are all that are needed to 'talk' to your vehicle. You need only send a few simple keyboard commands (ascii characters) and all the data formatting, error checking, bus arbitration, etc. is then handled by the ELM320 for you.

If you presently use one of our v1.x ICs, you will be pleased to know that this version (v2.0) is pin-compatible with your IC (the only difference is that linefeeds are now on by default). If your IC is mounted in a socket, you can simply unplug the old IC and plug in the new.

  ELM320P (8 pin PDIP): $14.50
  ELM320SM (8 pin SOIC): $14.50

ELM322 - OBD (VPW) to RS232 Interpreter (v2.0)

Similar to the ELM320, the ELM322 is for connecting to an OBDII equipped vehicle which uses the 10.4KHz J1850 VPW format. This standard is typically used in General Motors Corporation and some (Daimler) Chrysler vehicles.

As with all of our OBD ICs, the user need only issue the desired commands through an RS232 serial connection and the data formatting, error checking, bus arbitration, etc. on the vehicle side is taken care of by the ELM322. This allows experimenters to inexpensively create their own scan tool.

If you presently use one of our v1.x ICs, you will be pleased to know that this version (v2.0) is pin-compatible with the old, so you can simply replace your IC if you want to upgrade.

  ELM322P (8 pin PDIP): $14.50
  ELM322SM (8 pin SOIC): $14.50

ELM323 - OBD (ISO) to RS232 Interpreter (v2.0)

The ELM323 supports the ISO 9141-2 and ISO 14230-4 standards that are used by many vehicles throughout the world.

The ELM323 transparently converts between a 10.4KHz ISO data stream and standard ASCII characters, allowing trouble codes and operating parameters to be easily retrieved without the need for special software. No knowledge of data formatting, error checking, bus initiation etc. is needed either, as the ELM323 handles all of it for you.

The present version of the ELM323 (v2.0) provides several programmable features that the previous versions did not offer. It allows programmable header bytes, adjustable timeouts, the ability to report in the packed data mode, and offers a special monitoring mode as well. This is in addition to all of the capabilities that the v1.x ICs offered - the full seven byte command structure, two line (K and L) initiation, software selectable linefeeds and character echoing, and the visual feedback provided by the four LED outputs.

If you currently use one of our v1.x ICs, you will be pleased to know that this version (v2.0) is pin-compatible with the old, so you can simply replace your present IC with one of these, and immediately begin enjoying these new features.

  ELM323P (14 pin PDIP): $15.50
  ELM323SM (14 pin SOIC): $15.50

ELM325 - J1708 Interpreter (v1.0)

This protocol converter integrated circuit is for use with heavy duty vehicles that use the J1708 standard with J1587 or J1922. Although these protocols are being phased out (they're being replaced by J1939), there are still a very large number of vehicles that use them.

The ELM325 is a very capable product, as you would expect. You can monitor the data bus, selectively filter what you see, send messages, and retrieve replies, as well as adjust timing, priorities, output formatting, etc. all through a very easy to use ascii interface.

In use, the ELM325 is almost identical to our popular ELM327 and ELM329 products. A simple terminal program will get you going, and because it's ascii-based, custom interfaces are easy to create.

The ELM325 is a 14 pin CMOS integrated circuit that only requires a handful of components to make a complete interface tool. The output is serial, which allows you to connect to USB, RS232, Bluetooth, ethernet, Wi_Fi, other processors, etc. Have a look at our data sheet for a discussion on a couple of these (see the Example Applications section).

  ELM325P (14 pin PDIP): $15.50
  ELM325SM (14 pin SOIC): $15.50

ELM327 OBD to RS232 Interpreters

Version History

Elm Electronics has been producing the multi-protocol ELM327 integrated circuit since 2005. We have updated the product several times in response to your requests, and as a result have produced many versions of the IC over the years.

We are often asked just what the differences are between the versions, and so provide information on our 'obd help' page, and in the ELM327 data sheet. In addition, we also provide these two files ('ELM327 AT Commands' and 'Programmable Parameters') that summarize some of the programming differences.

Basically, you will find that the:

- Version 1.3a IC is a full-featured device that meets the needs of 90% of all users

- Version 1.4b update adds a reduced power (sleep) mode, and J1939 refinements

- The latest version (2.1) is faster, and has more features than any other version

ELM327 - OBD to RS232 Interpreter (v1.3a)
(a full featured IC at a lower price)

This integrated circuit has been the industry standard for many years. It provides support for all of the mandated OBDII protocols:

- SAE J1850 PWM

- SAE J1850 VPW

- ISO 9141-2

- ISO 14230-4 (KWP), and

- ISO 15765-4 (CAN)

in addition to variations on the above, and SAE J1939, etc.

You will find that it is very easy to use, and that there's a lot of support for it on the web (both construction ideas and software).

The ELM327 v1.3a has been replaced by the v2.1, but remains available because of customer requests.

  327P_V13 (ELM327 v1.3a in 28 pin PDIP): $17.00
  327SM_V13 (ELM327 v1.3a in 28 pin SOIC): $17.00

ELM327 - OBD to RS232 Interpreter (v1.4b)
(still available due to customer requests)

The main difference between the v1.3a and v1.4b chips is that the v1.4b offers the ability to go to a low power 'sleep' type mode. This is great for installations where it is preferred to keep the ELM327 connected to the vehicle (fleet applications, etc.).

There are also several improvements to protocol support which advanced users may find useful (control of the CAN silent mode, 4800 baud ISO/KWP, etc.).

Please note:
The ELM327 v1.4b is a mature product that has been replaced by the v2.1. We continue to offer this version for our customers that still need it, but we advise you to seriously consider using the v2.1 for any new designs.

  327P_V14 (ELM327 v1.4b in 28 pin PDIP): $21.00
  327SM_V14 (ELM327 v1.4b in 28 pin SOIC): $21.00

ELM327 - OBD to RS232 Interpreter (v2.1)
(our 'latest and greatest' version)

The latest version of our ELM327 integrated circuit provides all that the v1.3a and v1.4b products do, and also has:

- a 512 byte RS232 transmit buffer

- many improvements for speed and reliability

- an Activity Monitor, for going to low power and waking

- many new Programmable Parameters and AT commands

- frequency matching to prevent false CAN sends while searching

- the ability to process Response Pending replies

and many, many more improvements. If you were considering buying the v1.4b, then you will like the new v2.1 IC much better.

  ELM327P (28 pin PDIP): $21.00
  ELM327SM (28 pin SOIC): $21.00

ELM327L - OBD to RS232 Interpreter (v2.1)
(low voltage capable ELM327)

The new ELM327L integrated circuit is exactly the same as the ELM327 v2.1 integrated circuit, except that it:

- operates with supplies of 2.0V to 5.5V

- comes in three package sizes

- has a 2048 byte RS232 transmit buffer

- needs a capacitor on pin 6

If you need a smaller ELM327 IC, or one that works over a wider supply voltage range, this is it.

  ELM327LP (28 pin PDIP): $23.50
  ELM327LSM (28 pin SOIC): $23.50
  ELM327LSS (28 pin SSOP): $23.50

Please note that Elm Electronics only makes integrated circuits!

some Elm integrated circuits

You must build them into a circuit in order to use them.

If you want a 'ready-made' circuit (ie one with Bluetooth, USB, WiFi, etc.) then you will have to buy that from others. Some vendors do use 'cloned' integrated circuits, so if you want a genuine Elm device, be sure to ask the vendor what they use, and obtain their assurance that you can get a refund if you are not completely satisfied.

ELM329 - CAN Interpreter (v2.1)

The ELM329 is our CAN-only device that provides more CAN support than our popular ELM327. The ELM329:

- Supports ISO 15765, and SAE J1939

- Also has five user controllable protocols

- Supports CAN periodic (wakeup) messages

- Has a CAN Monitor for automatically switching to low power mode

- Provides single wire CAN transceiver controls

- Has general purpose inputs and an output

- Can send an arbitrary CAN message at any time

- Provides an 'active' LED

This latest version adds features that users have requested, improves code speed significantly over the previous chip, and adds new filtering for what we call 'CAN input frequency matching'.

The ELM329 maintains very good software and pin compatibility with the ELM327, so you will find the transition to this IC to be straight forward. Download a data sheet for all the information.

  ELM329P (28 pin PDIP): $21.00
  ELM329SM (28 pin SOIC): $21.00

OBD Software Development

ELM328 - OBD Device Identifier Test IC (v1.4)

The ELM328 IC is electrically identical to the ELM327 except that it offers one new AT command which can be used to reset the @2 Device Identifier lock. This provides code developers with a means to repeatedly test code which writes to the @2 device identifier, without requiring a new IC each time.

The ELM328 supports all of the ELM327 v1.4 AT Commands, but it does not transmit OBD messages - it is only for code development use, and is not intended for use in scan tools.

  ELM328P (28 pin PDIP): $28.00
  ELM328SM (28 pin SOIC): $28.00