OBD2 Won't Communicate - Can't Smog

[speedyspaghetti]

Hey everyone,

So I just bought a 2003 Z4 3.0 with 39k miles and I'm currently trying to track down an OBD communication issue so I can smog/register the car in California. The previous owner said he didn't have time to do the smog check, so I figured whatever, its $60, and lo and behold, here we are. The car itself actually runs and drives great - engine feels super healthy, transmission is smooth, no limp mode, no CEL while driving, etc. The issue only showed up when I went to get it smogged and the smog machine could not establish communication with the car at all.

My generic scanner (ANCEL AD310) also powers on and cycles through protocols (ISO, CAN, etc.) but eventually just says linking failed.

Here is what I have checked so far:

• OBD port power good
• Pin 16 = ~12.2V
• Grounds good
• Pins 4 and 5 both good
• Battery disconnected/reset performed
• Radio fuses pulled
• Head unit fully disconnected
• Soft top fuses pulled
• Amp was already unplugged by previous owner/mechanic due to parasitic draw issue
• Previous owner had GM5 replaced at some point
• Convertible top partially works
• Found standing water in battery compartment area during test drive - dried that up and cleaned minor corrosion from battery terminals. Battery voltage is good.
• Amp definitely appears to have had water exposure/corrosion at some point
• Drains were likely clogged

The biggest clue I've found so far is that pin 7 (K-line) only shows around 1.5V and slowly drops toward ~0.9V with ignition on. Pulling the radio/top fuses and disconnecting the head unit did not change this.

I ordered a Foxwell NT530 BMW scanner which should arrive tomorrow so hopefully that can at least tell me whether any modules communicate.

What else should I be checking? Has anyone else resolved this?

Thanks for any help!

 

[NZ00Z3]

You likely have a faulty module pulling he K-line bus down towards ground. K-Line should be 11.5V or there abouts when communicating.

Which module is faulty? Well, you will have to disconnect each one, one by one and test until you find it.

 

[vroomvroomman]

I had this issue too, as a matter of fact I still do! What works for me is while it's attempting to connect, turn the car off and on (pos 0 - pos 2 and back) around one or two times, and then it magically seems to connect. Not sure if this is also the case for you, but it's worth a try.

I have to do it every time with my foxwell scanner, though my Carly seems to not need that anymore. I also have a generic scanner which also sometimes needs that restart cycle. Super weird..

Edit: Seems I did not read correctly, this post is for a Z4, not a Z3, my bad.