ELM327-compatible adapters - how to choose

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ELM327-compatible adapters - how to choose

Post by FORScan » Fri Mar 30, 2018 9:52 am

We are asked every day about adapter's choice. The problem is that there is no easy answer, as there is no ideal adapter that would fit best every specific case. In this article we have tried to address most important issues of the choice problem in most compact way.

Note: For professional work we would recommend to consider purchasing J2534 Passthru adapters that support Ford protocols. ELM327 family is recommended for amateur and semi-professional usage. This article reviews only ELM327 familty of adapters. J2534 Passthru devices will be addressed in a separate article.

1. Protocols

Table 1.1 - Ford protocols
OBDII name / Ford name OBDII jack pinsBus speedBus min. response timeHow to detect
SAE J1850 PWM / Ford SCP2, 1041600 bps20...40 msImage
ISO9141 / Ford ISO79600 bps150...250 msImage
CAN / Ford HS CAN6, 14500 Kbps0...20 msImage
/ Ford MS-CAN3, 11500 Kbps0...20 msImage
/ Ford UBP310400 bps150...250 msImage
Table 1.2 - Ford protocols by model generations
P - primary protocol (PCM)
S - auxiliary protocol (not mandatory for FORScan)
GenerationSAE J1850 PWMISO 9141CANFord MS CANFord UBPComment
Ford 1996 - 2003PS---
Mazda 1996 - 2003-P---Some models used SAE J1850 PWM as primary
Ford EU, Mazda 2004 - 2009-SPS-Some models used SAE J1850 PWM as primary
Ford NA 2004 - 2009-SPSS
Ford, Mazda 2010+--PS-HS2, HS3 through MS-CAN
Simplest and quite reliable way to find out what protocols are supported in your car is to make a photo of the OBDII jack. Examples:
Focus Mk2 - only HS-CAN and MS-CAN
OBD2_focus_connector_small.jpg (37.97 KiB) Viewed 5652 times
Mondeo Mk3 after restyling - J1850, ISO9141, HS-CAN, MS-CAN
OBD2_mondeo3_small.jpg (36.54 KiB) Viewed 5652 times
Table 1.3 - Ford protocols by adapters
ChipSAE J1850 PWMISO 9141CANFord MS CANFord UBPAdapter
ELM327 standardXXX--ELM327, Kiwi 3
ELM327 with HS/MS switchXXXX-ELM327 marked as Ford, Mazda compatible
STN 1170XXXX-ELS27 (old versions), Viaken STN1170
STN 2120XXXX-ELS27 (new version)
2. Performance

Two parameters are mainly important for performance:
Min. interface respone time (minimal response time or ping) - minimal possible time from the moment request to adapter is sent to the moment the response from adapter is received
Max.interface baud rate - max possible data transfer baud rate between computer and adapter

These parameters directly affect connection time, parameter (PIDs) reading frequence, overall programming time

Table 2.1 - Adapters' performance
response time
baud rate
ELM327 OHP HS/MS WiFiELM327 (clone)WiFi30-40 ms38400 bpsUnknown manufacturer - "good clone". Recommended only for iOS
Kiwi 3ELM327 compatibleBluetooth Low Energy40 ms-Can be used only with FORScan Lite for iOS
ELM327 HS/MS USBELM327 (original)USB0..2 ms500 Kbps
OBDLink SXSTN1100USB0..2 ms500 Kbps
OBDLink LXSTN1100Bluetooth--
OBDLink MX BTSTN1150Bluetooth8..20 ms115200 bps
OBDLink MX WiFiSTN1150WiFi-115200 bpsWiFi interface works unstable - it freezes and times out. Strongly not recommended!
ELS27 v3STN2120USB, Bluetooth0..2 ms USB,
20 ms BT
8 Mpbs USB
Viaken STN1170 USBSTN1170USB0..2 ms2 Mbps
Viaken STN1170 BTSTN1170Bluetooth20..30 ms38400 bpsMay freeze on some cars. Not recommended
Overall system performance can be easily estimated by adapter's performance and bus parameters as the following:

Overal min.response time = Min. adapter response time + Min.bus response time
Overal baud rate = MIN ( Adapter max. baud rate / 2, Bus baud rate)
Example 1: Ford Mondeo Mk3 PCM, bus J1850. Adapter ELM327 OHP HS/MS WiFi. According to the table 1.1, let's assume min. bus response time is 20 ms, bus baud rate is 41600 bps. According to the table 2.1 adapter's min response time is 40 ms, baud rate is 38400 bps.

Overal min.response time = 40 ms + 20 ms = 60 ms
Overal baud rate = MIN ( 38400 / 2, 41600) = MIN ( 19200, 41600) = 19200 bps.

Note: we divide interface baud rate by two because ELM327 family adapters exchange data in text format. So every machine byte is represented in 2 transferred bytes.

As we can see, the adapter significantly limits the overal system peformance in this example (in case of cars with CAN bus, like Mondeo Mk4 or Mk5, the test results would be much worse). Is that bad? Well, it depends on your goals. If reading DTC and some PIDs is the only objective you have, it is not too important. But if you plan to read PIDs in real-time (or as much close to it as possible) or perform programming (actual for CAN bus), then this adapter is a bad choice.

Example 2: Mazda 323 2001, bus ISO. Same adapter.

Overal min.response time = 40 ms + 250 ms = 290 ms
Overal baud rate = MIN ( 38400 / 2, 9600) = MIN ( 19200, 9600) = 9600 Kbps.

In this case the adapter is OK, because the bus itself is very slow. Reponse time is less than 20% higher than maximum possible for this car, and transfer speed is also limited by the bus.

Example 3: Ford Fusion 2015, bus CAN. Adapter ELS27 v3 USB. Let's assume CAN bus response time is 0 ms, and adapter has 2 ms of response time and 2 Mpbs baud rate.

Overal min.response time = 2 ms + 0 ms = 2 ms
Overal baud rate = MIN ( 2000000 / 2, 500000) = MIN ( 1000000, 500000) = 500 Kbps.

So in this case the response time is minimal, and baud rate is limtied by the CAN bus one.
3. Reliability

Two things are important for reliability:

- quality of the adapter. Not original adapters in general case have lower quality than original ones. We will create a dedicated article about so-called "clone problem".

- type of interface. The fact is that wireless interfaces used in ELM327 family of adapters are much less reliable than USB interface. And this problem is actual not only for "clones", but also for "original" adapters (OBDLink MX WiFi and Viaken VScan Bluetooth are most obvious examples).

So in general case we recommend to use USB for Windows version of FORScan, where it is possible. BT and WiFi devices are only recommended for mobile platforms (iOS and Android).

Also, important note about adapters with mechanical HS/MS switch: in addition to the fact it is not very convenient to switch it manually, it may be not possible to perform some operations with this type of adapter. If some operation requires a simultaneous access to both HS and MS (so FORScan needs to access some module(s) on HS CAN bus and, at the same time, other modules on MS-CAN bus), it cannot be normally executed using adapters with mechanical switch. Example: reading parameters (PIDs) in virtual module All, Module initialization subfunction in service functions "Remote keyless entry and Start".

4. Recommendations

Table 4.1 - recommendations on adapters
NO - not recommended for this platform
D - recommended for diagnostic: read PID, read/reset DTC, simple service functions
C - recommended for configuration: write configuration parameters to modules, complex service functions
P - recommended for programmign: complex configuration, firmware update (only for CAN )
AdapterFORScan for WindowsFORScan Lite for iOSFORScan Lite for Android
ELM327 OHP HS/MS WiFi (clone)NODNO
Kiwi 3NOD (if MS-CAN is not required)NO
OBDLink SXD, C, P (if MS-CAN is not required)NONO
OBDLink LXD (if MS-CAN is not required)NOD (if MS-CAN is not required)
ELS27 v3D, C, PNOD
Viaken STN1170 USBD, C, PNONO
5. Links to original adapters

All of these adapters were tested by us

5.1. ELM327 HS/MS USB: http://elm-327.eu/

Update 2018-05-11. Note: this company also sells standard ELM327 BT (without HS/MS switch) that may NOT work properly with some models as Bluetooth chip may freeze on requests that receive a lot of data (same problem as in Viaken BT described above).

5.2. Kiwi 3: https://www.plxdevices.com/ . Note: this adapter is only supported by FORScan Lite for IOS! FORScan for Windows and FORScan Lite for Android have no support for this adapter.

5.3 ELS27: http://els27.ru

5.4. OBDLink product line: https://www.scantool.net/

5.5. Viaken: https://viaken.pl/pl/polski-elm327-v3-f ... -2014.html

Note: actually, all what we write about Viaken adapter is related to older version (v1 or v2, in black case). We had no chance to test their v3 version yet.

6. Links to other adapters

6.1. Elm327 HS/MS OHP good clone: https://www.amazon.com/OHP-Forscan-comp ... Ford+Mazda

It not original, but there is no better alternative for FORScan Lite for iOS yet.

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Re: ELM327-compatible adapters - how to choose

Post by dickiefrank » Sun Jun 03, 2018 1:42 am

I'm getting a reading on the forscan when I try to link it to the truck...says "bad clone"...my connector does not have the toggle switch...am I to conclude that I need the one WITH that toggle switch?

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Re: ELM327-compatible adapters - how to choose

Post by Vladsky » Sun Jun 03, 2018 12:22 pm

dickiefrank wrote:I'm getting a reading on the forscan when I try to link it to the truck...says "bad clone"...my connector does not have the toggle switch...am I to conclude that I need the one WITH that toggle switch?
The proper adapter you need is already specified above.

Suggest you start reading, Dickie :lol:


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Joined: Sat Jun 09, 2018 2:41 am
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Re: ELM327-compatible adapters - how to choose

Post by nixoid » Sat Jun 09, 2018 4:13 am

Vladsky wrote:
dickiefrank wrote:I'm getting a reading on the forscan when I try to link it to the truck...says "bad clone"...my connector does not have the toggle switch...am I to conclude that I need the one WITH that toggle switch?
The proper adapter you need is already specified above.

Suggest you start reading, Dickie :lol:

I haven't looked at too many threads yet but every post I've seen from you has the voice of a troll. Instead of just telling people to read like they're stupid or lazy, try helping out. Not everyone can understand technical info as well as you.

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