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-   -   Z4 SRS Code 38 swinging voltrage test (

Trapper 01-28-2013 06:09 AM

SRS Code 38 swinging voltrage test
Hi Guys,

I need your help. Here is the background info. I had my passenger seat out of my car to repair the seat tilt mechanism. Never put the key in the ignition while the seat was out. Reinstalled the seat and check dash lights - no air bag issue:thumbup:.

A few days later I was installing a battery tender because the car will be stored for the winter. The ignition was off but I was listening to the stereo as I was installing the lugs onto the battery terminal posts the radio cut out very briefly but came back on. I guess as I was attaching the battery tender lug I momentarily disconnected the battery. The radio kept playing so I was relieved I didn't have to worry about radio codes. The next time I started the car I noticed the air bag light (red) was on. So I bought a B800 SRS scan reset tool.

The SRS gave me a table 01 code 38 Control Unit Fault - Swinging Voltage Test.

I figured it would be a simple reset because I disconnected the battery but I am unable to reset it :dunno:. One thing to mention is I did have the battery tender going when I did the scan and attempted reset. Not sure if that is affecting things. Also The car never left the garage between reinstalling the seat and hooking up the battery tender.

I searched this forum and the web without any luck.

Any suggestions?

Blacklane 01-28-2013 04:26 PM

SRS codes don't clear with a battery power cycle; you need an SRS reset tool. There are some BMW SRS reset tools on e-bay for about $35 US.

I honestly don't know anything about that test, but the name implies that it is a system start-up test that looks for a stable power supply voltage. It could have been triggered by the system starting with only the battery maintainer and no battery to stabilize the voltage.

Good Luck.

Trapper 01-29-2013 05:19 AM

I have a B800 reset tool thats what I used to read the code and try to reset the code. The battery tender was not plugged when I was hooking it up to the battery. So the only "swing" in voltage would have been when the lug came loose from the battery post for a split second.

Is it worth trying to disconnect the battery for 20 minutes then reconnect the battery and try a reset or will I get into bigger problems?

I have read other posts where guys get airbag light activated when they change batteries or their battery dies. They just reset the airbag with a SRS tool. That's why I bought one.

Blacklane 01-29-2013 05:29 AM

Are you saying that you cannot reset the SRS code with the reset tool?
If a code is cleared and comes back on the next start-up cycle, then the fault still exists and needs to be fixed.
If the code will not clear, then it probably means a bad SRS control module.

Trapper 01-29-2013 05:40 AM

Yes that's my point. I tried to reset the code using my B800 tool but could not get it reset. Since I got the code when I disconnected the battery for a split second. I figured it would be a simple reset.

I guess my question is where should I start looking to trouble shoot the swinging voltage fault?

Blacklane 01-29-2013 05:47 AM

Could be a bad reset tool.

pokeybritches 01-29-2013 12:01 PM

I got an airbag light despite never touching the ignition when I pulled my passenger seat out. I should have disconnected the battery. I don't know much about your reset tool, but I would confirm that it works with the Z4. Many don't. I won't be reunited with my car for another few months, but I'll pull the code when I am and pass on an update.

There are a few threads over on zpost regarding software.

Edit - just found this:

Amazon Link

"Didn't work on my 2003 BMW Z4, despite advertisement to the contrary. Took car to dealer for reset with dealer computer. Car reset fine, no problem. I had simply removed the passenger seat to do a little maintenance and the SRS light was latched on."

Trapper 01-30-2013 06:31 AM

Thanks Pokeybritches,

I look for to hearing back from you on the codes. I read the reviews on Amazon before I bought the unit and I did find the reviews mixed and decided for the money I would give it a try.

This weekend when I am back in town I will try disconnecting the battery tender and the battery for twenty minutes. I will check the battery voltage to see what state it is in, then reconnect the battery and see if I can reset the fault.

pokeybritches 01-30-2013 02:26 PM

Disconnecting the battery won't reset the light. It has to be reset by the dealer or with a very specific tool. I think software + USB/OBD2 cable is your best option.

Hornedfrog1969 01-31-2013 08:34 AM

the B800 SRS is the "very specific tool" you are refering to. The aribag light can only be reset through the port under the hood and not the OBD connector.

The tool description says it is compatible with the Z4. Perhaps the battery tender is the source of you issues.

pokeybritches 01-31-2013 01:03 PM


Originally Posted by Hornedfrog1969 (Post 7350615)
the B800 SRS is the "very specific tool" you are refering to. The aribag light can only be reset through the port under the hood and not the OBD connector.

I'm aware that the Z4 is listed as a model that the tool works with, but if you read the reviews, someone posted that they bought it and the tool would not reset the light on his 2003 Z4 (what I quoted). The tool may be able to reset the light, but others haven't had success with it on the Z4. If the OP is able to reset it, I might buy one myself :) My reasoning for removing the passenger seat was measure resistance changes in the weight sensor with and without passenger. I've created a circuit that replaces the weight sensor in the passenger seat, allowing the user to manually turn on or off the side airbags and avoid an airbag light when using aftermarket seats. It would be nice to be able to see if it works without fear of having to go back to the dealer again to fix the light.

My point (and I think we both agree with it) is that a general code reader will not reset the light, and neither will unplugging the battery for 20 minutes. The airbag light is a different beast, and the non-Ebay reset tools I've seen for sale run upwards of $600. There is software available for $30 or so that will fix the light. Despite what the manufacturer claims, I would be inclined to question the tool's ability to reset the light before moving to the conclusion that a problem is persistent.

Where do you go from here?

1. Find someone that has gotten the tool to work on the Z4. If they have, then you have an ongoing problem that needs attention.

2. Go to an independent mechanic that has an airbag reset tool and see if they are able to reset it.

3. Go by the dealer. Ask them how many times the fault has appeared, and ask them to reset the light. Don't have them do any additional work for you. I've had my airbag fault light come on 3 times - once after the driver's door was taken apart by a body shop to fix a window regulator; again after I jump-started the car; and finally after I took out the passenger seat. With the jump-starting incident, the dealer recommended thousands of dollars in parts and labor. I asked how many times the fault had appeared, and the SA said only once. I told him I'd take my chances, and it never reappeared until I took out the passenger seat several years later.

4. Check Zpost and buy the software and USB cable they recommend.

Hornedfrog1969 01-31-2013 01:44 PM

I had considered that there may be a difference in how well this device works with a Z4 versus a Z3. I can tell you that it works great with a Z3. I have turned off my Airbag light twice after removing the seats as well as three other people cars who had the light on. If it is discovered that it in does not work on the Z4 as advertised, then he should get his money back.

pokeybritches 02-01-2013 05:52 AM

Good info! I agree.

OP - maybe I misread the post before, but are you trying to reset the light with the battery tender still connected? I would definitely disconnect it and try the reset.

How do you have the battery tender connected? Directly to the battery, or via the jump terminal under the hood?

Trapper 02-11-2013 10:47 AM

Sorry for the late reply I was away on vacation:drink:

I have the battery tender connected directly to the battery. That's how this whole thing started as I loosened then removed the nut on the negative post to put on the battery tender lug I temperarily lost connection between battery and cable.

I did try resetting it with the battery tender disconnected and still no luck. One thing I noticed is that my battery voltage was only 12.5 volts after I unplugged the tender. I would have expected the voltage to be higher.

Also, I was using the tool connected to the OBD port however will try resetting using the connection under the hood as Hornedfrog mentioned.

PhoenixBlue 03-25-2013 09:30 AM

Hey Trapper, Did you ever get this tool to work with your Z4? Am curious as I'm thinking of purchasing it as well!

Trapper 03-25-2013 10:16 AM

I have been researching this issue for a while now and read in a post somewhere last week that someone have the same issue while attaching a battery tender. In this other guys case he took it to the BMW dealer and found the problem was some dirt got in between the battery post and the connector causing the swinging voltage code.

So I had a Eureka moment thinking I had the same problem. So this past weekend I took apart and cleaned both battery posts and connectors with emery cloth, removed any residue with a clean rag then reattached and tightened the crap out of them.

Hooked up my Air bag scan and tried to reset's still there:mad:

I am dropping the car off tonight to get some service done (tranny spill n fill, diff fluid changed) and will ask the technician to see if they can clear the code. Once I hear back from them then I will know if my tool is a piece of crap or I have a fault somewhere that I did not fix so in that case maybe my tool is okay.

Will let you know next week when I get the car back.

PhoenixBlue 03-25-2013 12:03 PM

Thanks for the update, Trapper! Hope the dealership will be able to help with this weird issue - perhaps you could get them to test with a new/different battery as well?

Trapper 04-18-2013 09:49 AM

Just getting feedback from my mechanic regarding the SRS code now. He said there where two codes (1) swinging voltage due to letting the battery get too low and (2) passenger seat belt fault which I created when I removed the passenger seat without first disconnecting the battery. He had no problem clearing the codes.

So I guess the $40 I spent on the B800 scanning tool was a waste of cash and a lesson learned.

PhoenixBlue 04-18-2013 10:37 AM

Agreed. I just returned mine as well.

I found someone with a professional scanning tool to read the code and clear it. He only charged me $40 :D

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