I searched SRS-B00021A on here and didn’t find anything so I’m starting this thread so that we can go on the adventure of getting this issue resolved together and make life easier for the next person.
So diving into this code a little bit, I see from SRS-B00021A – Volvo Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis that it’s “Driver Frontal Stage 2 Deployment Control. General Electrical Failures. Circuit Resistance Below Threshold”. After doing some research (asking ChatGPT) I understand that “Stage 2” is a high power mode of deployment, so basically there are 2 sets of wires to the airbag, on startup the computer takes resistance on them and it sees the “Stage 2” wires have a short.
Now, on tsbsearch.com there is exactly 1 service bulletin which contains this code, that is TJ 22855 Volvo Technical Service Bulletin – the content of which can be found here: Volvo TSB TJ-22855 — 2010 XC60 | CarComplaints.com
This TSB says: VOLVO: AIRBAG SYSTEM SERVICE REQUIRED MESSAGE IN DIM, DTC SRS-B00021A. THE CONNECTOR FOR THE CLOCKSPRING DOES NOT DEPRESS AND DISENGAGE THE SHORT CIRCUIT BAR ENOUGH. *PE UPDATED 5/16/11. *PE UPDATED 5/17/11. *PE
As I said, the shop which did the pre-purchase quoted me for a new clockspring, but I wanted to have a stronger understanding of this issue before I go and buy a new clockspring and just try to swap it in.
- What is the “short circuit bar”? I know what one is in the general sense, but what and why does it exist in this car?
- Does the clockspring mechanically push on it? Is it a physical defect that it doesn’t push enough?
- If I buy a new-used clockspring, is there any guarantee it will push the short circuit bars any better than the old one?
After some more searching, I discovered this: PPT – AIRBAG AND PRETENSIONER CIRCUITS PowerPoint Presentation, free download – ID:6014463 nice little slide deck about how modern safety mechanisms work. Apparently the shorting bar is in fact part of the airbag connector clip which clips to the clockspring.
So I gather:
1. This problem is likely to be fixable simply by disassembling the steering wheel, unplugging the airbags, and plugging them back in (perhaps a bit more firmly)
2. There are likely 2 kinds of clocksprings, the ones from 2010 and earlier, which have the bug, and the ones from 2011 and newer which have been physically updated not to have it.
But my question remains: If there was a physical update to the clockspring, how can I buy The Cheapest Thing On Ebay which has that update?
If I had the software to be able to check what part numbers were used in what years, I would probably be able to look this up rather quickly, but what I was able to find from sleuthing around was:
- There’s a clockspring on ebay pulled from a 2010 Volvo XC70 (this car has the bug) and it has part number 31313818
- There are a number of other clocksprings available with part number 31313854, all are pulled from 2011 and 2012 cars which seem to be fine
- volvowholesaleparts.com shows part number 31343218 replaces 31313818 AND replaces 31313854.
Maybe someone with the Volvo authorized repair software can chime in and give the entire lineage of this part, but it seems that 31313854 has this specific issue fixed, but it too was superseded for other reasons.
So as far as I can tell, the situation is this:
1. It’s a physical defect, it is not an electronic issue, and not a wear issue
2. Therefore, any old replacement part from a wrecked car is just as good as any other, as long as it has the right part number
3. However, searching “volvo 31343218” on ebay pulls up $50 offers for new ones ($25 for used) so I might just buy a new one anyway.
My next steps will be to buy the new part, disassemble the steering column, compare the new and old parts with some photos, reassemble, an try to reset the code.