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Land Rover Repair/OBD II Data link connector error to SMOG


QUESTION: Hello John,

I have a peculiar situation on my 2001 Range Rover HSE 4.6. I cannot get the vehicle to pass the CA smog certification, for reason that the vehicle cannot communicate with the CA state OBD II system.  Whereas any OBD2 system handheld or otherwise, including the dealership functions properly. But when I go to the sanctioned state SMOG stations the systems cannot communicate with my vehicle... a Data Link connector error condition.
Now I also noticed my Nav console display is blank (no menu), could this be related to the OBD2 fault.

ANSWER: I can't say what's wrong without seeing your car but I can say for sure that other Rovers talk to the CA smog systems.  The only suggestion I have before directing you to a Rover specialist is this:  Did you try more than one smog test station?  If two of them can't read your truck I think we can safely say the issue is in the truck itself.

The Nav or another system may be stuck and tying up the data link signal lines.  

We have fixed a number of problems like that over the years but there is no single cause to point you to.  Even corrosion at the connector is a possibility.

---------- FOLLOW-UP ----------

QUESTION: Thank you for the response.
Yes, I have visited an many as five smog stations and the state of CA SMOG referee, with each system displaying the same problem with the communication. Absent this data link issue, the car runs fine, no service engine light on the dash. I had visited the dealership diagnostic shop and they have the OBD2 was functioning properly there also. When you suggest that the Nav system may be stuck, hence tying up the data link signal line, where or how do I look for that to trace the connector for corrosion or the grounding .

What I would do is look at what devices are talking on that line (engine, brakes, SRS, nag, climate control)  I'd unplug them one at a time and see if the state inspection comms problem disappears.  I suspect it will.  

I know you were hoping for a more comprehensive answer, but the next step is going to be pretty time consuming.  Someone is going to have to get out the wiring diagram for the car, and then begin disconnecting each of the devices that talks on the OBD II comm lines one at a time.  After each disconnection, you'll have to try connecting to a machine like the state tester that has a problem, to see if the problem is cleared up

You hope for a quicker or more targeted answer but I'm afraid one does not exist.

What is probably happening is thisL  The generic OBD II scanners used in repair shops only connect to some of the circuits in the OBD II connector.  The state test system may be connecting to more, and the problem may lie in there.  If you had access to a factory level test system you could read all those things, but without it, you are left with sequential test as I describe.  Even with a factory test system you might still be left with manual testing to be sure

It's up to you to take it from here.  This is a free support forum where I try to give quick and (hopefully) correct suggestions to point owners toward solutions.  It's not meant to be me, diagnosing cars by remote control.

Best wishes

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John Elder Robison


I own J E Robison Service in Springfield, MA. We are Bosch Car Service for Land Rover, BMW, Mercedes, and other European lines. I can answer most questions about Land Rover service or repair. I'm known as a car enthusiast, machine aficianado, photographer, writer, and speaker. I've been around Land Rovers and British cars most of my life. Visit me at my car business, or my author website, Check out my autism and writing blog at or my photos on John Elder Robison


I have been a Land Rover service manager since Land Rover returned to North America in 1987. My company is a four-star Bosch Car Service facility, known nationwide for Land Rover service, overhaul, customization, and restoration. In addition to Land Rover our company services BMW, Jaguar, Mercedes-Benz, Rolls_Royce, and Bentley motorcars. We have factory-plus-level service capability for all makes. Visit my company online at > service > land rover Also visit my blog at


In the Land Rover world, my writing can be found in various print magazines and online at robisonservice.blogspot,com. In the wider publishing world, my work is published by 20 publishers in over 50 countries. Mt books Look Me in the Eye, Be Different and Raising Cubby have made US and international bestseller lists.

I am ASE certified, Bosch Trained, and trained by Omnitec/T4 and Autologic on their Land Rover test systems.

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