MGs/Rovers – Not 100% EOBD/OBD II Compliant

The ElmScan 5 tool I received a few days ago from scantool.net seemed a little strange. I attempted to connect it to my laptop and the car and communicate with it but I kept getting interface not found.
I tried hooking it up with hyper terminal to the virtual USB com port and as soon as I made a connection, the power LED on the scantool would go.
I found it quite strange that none of the other LEDs were even attempting to light. Doing some research, I discovered that when you plug the scantool into the ECU, that a LED sequence should occur to show correct operation of it.

I spoke to one of the main guys at scantool.net and he was quite surprised since each tool is tested fully before it leaves the warehouse (excellent QA from that company).

So the ElmScan was not getting power, but how is it that my other ‘fake’ ELM327 device gets power and my hand held fault code reader gets power. I was told by the guy I was talking to that the ElmScan uses pin 5 of the DLC connector as ground and pin 16 to get power. Doing more research into the pin outs, it appears Pin 16 is Battery power and Pins 4 & 5 are grounds, chassis ground and signal ground respectively. I had a +12 voltage across Pins 16 and 4 but nothing across 16 and 5. This clearly was the problem.

EOBD DLC Connector

EOBD DLC Connector

So then I got out my volt meter and investigated. I had a +12 voltage across Pins 16 and 4 but nothing across 16 and 5. This clearly was the problem.

Voltmeter used

Voltmeter used

The guy I was speaking to from Scantool.net kindly gave me a hint suggestion to short jumper 1 on the ElmScan. This means that it will take Pin 4 as the ground which is all my car will offer as ground. Opening the tool was surprizingly simple, no glue or anything. I took the circuit board out and grabbed a jumper from old computer parts and placed it on the create the short.

ElmScan 5 USB with JP1 set

ElmScan 5 USB with JP1 set

Alternatively if you don’t have a spare jumper, you can soldier the pins together with a piece of wire.

I hooked it up to my OBD connector on the car and it worked instantly. I loaded up the software and connected USB just to be sure and it connected fine. The tool was sending out 4 samples a second which isn’t too bad. When I revved the engine, the response time was satisfactory. As far as I know the more parameters that I add to request, the slower the response will be but I’ll have to investigate that over the next few weeks.

So in fact MGs/Rovers don’t seem to be 100% EOBD/OBD II compliant – only on a physical level though. Most scanning hardware would work but some don’t and the reason is that pin 5 is not used by MGs/Rovers.

Saturday, February 7th, 2009 ELM327 Interface, Onboard Diagnostics (OBD)

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