FAULTY ELM 327 INTERFACES DE-MYSTIFIED (READ HERE)

[ruda30]

Hi,

A lot of people are having problems with some chinese ELM interfaces that cannot connect to CAN network even if they support all ELM 1.3 commands properly. There was one user here who bought 5 of these cheap interfaces with no luck and finally bought an expensive one....
I also have one of these "faulty" units and decided to play with it and see what is wrong.
Well, it seems that the problem is electrical and is not very hard to fix.
The problem is actually in the CAN termination method used in these interfaces - they use one 120 Ohm resistor connected between CAN-L and CAN-H.
According to the ELM327 datasheet the proper termination is to use 100 Ohm resistor on each of the 2 lines connected to ground through a 560 pF capacitor (see the picture below).
So i just got two 100 Ohm resistors and two capacitors of 560 pF and fixed my interface as shows below. And it WORKS flawlessly now.
The procedure is very simple:
1. Get two resistors of 100 Ohm and 2 capacitors of 560 pF.
2. Remove the single terminating 120 Ohm (or whatever) resistor from the interface
3. Solder the new termination circuit. I did it directly on the OBD connector as it was easier for me. I did it in a hurry just for the so don't blame for the soldering quality on the pictures.
4. Go to your car and enjoy....

NOTE: It is reported that most of the new interfaces now have this problem!
It was also reported by many users that the problem can be solved by simply removing the 120 Ohm termination resistor (which is connected between the two CAN lines, it is R14 on my photos but might be marked with different number on other interfaces) from the interface.

Please, someone with knowledge in the circuits to explain these better as I don't have time for more details.

PLEASE NOTE: This post is for interfaces that respond properly to all ELM commands in my "Test" which is in the Settings dialog (all commands should have response OK). If you have OK to all commands and can connect to engine, but cannot connect to anything on the CAN bus (like Body Computer, Dashboard, Service Reset) then this post may help you.

elmfix1.jpg

elmfix2.jpg

elmfix4.jpg

elmfix5.jpg

elmfix6.jpg

Yani

Ahoj prosimtě na jake piny mam pajet resistors a capacitor natom fotu to nejde vydět

[hunter555]

After fixing the wiring everything is working properly.

Big thanks!

[Alfaeddy]

Hello
I figured that there is a setting error.
Since my BT interface with the ID without CHX modifiktation functioning.

Greetings Eddy

[gotberg]

Hi all!
Just a tip if you are going to buy an interface, I just got mine from China and it works without any modifications.
http://www.aliexpress.com/snapshot/103129304.html
Fast shipping and the price USD 14,74 (fre shipping)

Thank You!

[pls]

@ pls

Your test your Inteface is very interesting,

Since the Comand ATZ and one ATI Elm 327 v1.4 is detected.
Until then have all my work area in the CAN interface

Could you ever set a picture of your board here?
Front and rear


Greetings Eddy

@Aflaeddy

I can send pictures but my interface has the same layout as in the post I replied to
(viewtopic.php?f=5&t=1493&sid=c9a1a9d51d ... t=10#p3808)

I have modified my interface so its 1-7-9-12 pins are shorted but before that it was also not working.

[Alfaeddy]

Hello

If your layout is the same, then it must also work!
I think it is a setting error!

Probably the FTDI driver is missing for the interface
http://www.ftdichip.com/Drivers/VCP.htm

If your ELM interface correctly identified in the Control Panel?
and set the correct com port?

I also thought of this picture FES / setting / interface / test
which is an interface with the resistor R04



Greetings Eddy

[pls]

@Aflaeddy

I can connect successfully with ECU and ABS, so, the driver is there and works fine, interface is identified and it is communicating over COM port. But I'm not able to access any of CAN modules. Scanning identifies only ECU and ABS. I have attached photos of my board.

I'm placing also again of interface test, that shows that there is communication with the interface:

Code: Select all

Scanning ...

ELM 327 interface found at port COM2, speed 38400bps
This interface is compatible with ELM 327 1.3! Should connect properly with all CAN modules.
Latency Too High!!!

Code: Select all

COMMAND: ATZ
RESPONSE: ATZ



ELM327 v1.4a

>

COMMAND: ATI
RESPONSE: ATI

ELM327 v1.4a

>

COMMAND: ATE0
RESPONSE: ATE0

OK

>

COMMAND: ATL0
RESPONSE: OK

>

COMMAND: ATH0
RESPONSE: OK

>

COMMAND: ATSPC
RESPONSE: OK

>

COMMAND: ATS0
RESPONSE: OK

>

COMMAND: ATCAF0
RESPONSE: OK

>

COMMAND: ATCFC0
RESPONSE: OK

>

COMMAND: ATCRA 7B0
RESPONSE: OK

>

COMMAND: ATSH 7B0
RESPONSE: OK

>

COMMAND: ATAT1
RESPONSE: OK

>

COMMAND: ATST41
RESPONSE: OK

>

COMMAND: ATBI
RESPONSE: 
ERR94

>

WARNING: This interface is not compatible with ELM 327 1.3! Will not connect to any CAN module.

[Alfaeddy]

@ pls

Very strange, in your board should be ok CAN connection
But after you have an error in TEST
Comand ATBI = ERR94

Unfortunately I can not tell you why this error occurs
Such an error I do not know.?
And I've had some interface

I suspect that your interface when resoldering broke ?

Really such a mistake I have not seen yet.

Greetings Eddy

[Mozella]

Here's another data point.

I recently purchased a cheap Ebay version of the ELM 327 interface. Like others who have reported earlier, I could see the ECU data for my 2007 Alfa Spider 2.2 JTS and it passed the test routine, but I could not access any CAN information. My circuit board is very similar to the picture posted by ruda30 near the bottom of page 13.

I removed the resistor labeled as R14 and now it works as I hoped.

By the way, this resister is on the "bottom" side, opposite from the LEDs. The label is printed in such a way that it might actually be RI 4 (R-"letter eye"-space-four) or R=Fourteen or even R-One-space-Four. In any case, removing it makes the CAN data available.

[eric.dervel]

Hi,
I am new here, and i never used this software. Before FES i use ,,TORQUE,, on android phone, but this is much better. But i have problem with the connection....
I can't connect my ELM327 Bluetooth adapter with the software on Fiat Bravo 2008 t-jet. I don't know am i doing something wrong or i need to remove some resistor (if so plese tell me which one). I am on Win 7 64bit. THANKS