Ronjo C.

Hi All,

I'm new here but a regular on a few other car forums. For the most part, my 2007 ML320 CDI has been flawless and the few little questions I've had the search feature has solved everything for me perfectly! This one, I've tried google and searching every Mercedes and Jeep CRD forum I can find. Nothing yet! So here's my question to you guys: Up until a few weeks ago, I could put the key in the ignition position (engine off) and use my OBD2 scanner. Recently, I had an error that my device couldn't connect. That's odd. I turned on the engine and instantly I could connect. Turn off the engine, back into the ignition position and suddenly no connection again. Engine on, no issues.

What on earth could be causing this? I'm planning to do a tune on the car soon and there's no way I can tune with the engine running. Any thoughts would be greatly appreciated.

Thanks All,

RonJo

mbdiesel12

I can't explain why it worked with the key completely out. The OBD2 protocol calls for power to be supplied to the scanner. Usually you turn the ignition to the "accessory" position to connect so the scanner can begin identifying the specific protocol the vehicle is using and begin downloading information. If you start the car, it can then read "real time" data from the vehicle.

Without turning the key to a "power on" position (ie-position 2 or accessory) I can't understand how it ever connected unless your ignition is supplying power to something as soon as the key is inserted. Some vehicles supply power as soon as the key is inserted to power the anti-theft system. I know Porsche does that. Maybe you have a fuse blown or something.

Try turning the ignition to accessory mode without starting the engine and see what happens.

Ronjo C.

Sorry if I wasn't clear. Let me rephrase, key in, accessory position previously worked fine. Now, key in, accessory position does not. Key in, engine running, scanner works fine. Turn off the engine and put it into accessory position and it doesn't work again.

I tried it in my Audi TT-S and it works in the accessory position and the engine on. I also tried it on the Volvo XC60 that I have access to and it works in both the accessory position and the engine running.

mbdiesel12

Try jiggling the key in the accessory position to see if it connects. Maybe your ignition lock is starting to get loose. Do other functions work in accessory position?

mbdiesel12

Check your battery to make sure you have 12V with the engine off. Some scan tools won't operate with much less than 12v at the connector port. Also, let the vehicle cycle through its start up and chime process before you plug in the scan tool.

The connector port can be checked for 12v by a knowledgeable person. If you have no voltage at the connector you may have a blown accessory fuse somewhere.

Micah / AF1 Rac

mbdiesel12

If you're comfortable using a multimeter you can test for 12v at the OBDii port. Pin #4 is a chassis ground and pin#16 is 12v positive.
The pins are numbered as follows:

Top row, left to right are pin #'s 1-8
Bottom row, left to right are pin #';s 9-16

You should see 12v when testing between ground pin #4 and the positive pin #16.

Caution: Make sure you test the correct pins and don't short anything in the process. Don't test if you're not comfortable.

Do a Google of the OBD port pin locations as a guide.

Note: Pin #5 is called a ground but it is used as a communication ground. Use the chassis ground, pin #4