1990 740 - SRS light on, dash fan not working - intermittent

GSmith · Post by **GSmith** » 16 Apr 2009, 19:52

Gee, it's a busy Volvo day for me...

Since last night, the SRS light sometimes comes on when I start the car, and sometimes not. When the light is on, however, the dashboard fan doesn't work (I might assume other things like the radio or the cigarette lighter don't work as well, but they're not currently hooked up).

So, could something for the airbag and the dashboard fan be on the same fuse that only gets power sometimes????????

DeRail · Post by **DeRail** » 17 Apr 2009, 11:00

Was going to post in here last night about a similar problem I'm having with the '88 760. The SRS light will come on sometimes when starting the car sometimes not. Today when it came on, I tested my blower and sure enough it was not functioning. The SRS was flashing at an irregular pace while waiting at a traffic light (indicating to me a loose connection, maybe). After I stopped for a few minutes at the light, the SRS light went off and stayed off and my blower was working again. Any ideas on how to fix this?

btw- radio was working while all of this was happening, didn't try the ciggy lighter

edit: just ran an errand, radio wouldn't turn on... pulled radio, amp and airbag fuses, and reseated... so far so good. Anything else I should look into?

Post by **billofdurham** » 17 Apr 2009, 12:31

Oh boy, a twofer.

There is no direct link between the SRS light and the heater fan on either car.

On the 740 fuse 6 (30 amp) is for the heater fan for the ECC sytem. Fuse 16 (15 amp) is for the heater fan A/C.

On the 760 fuse 28 (30 amp) is for the heater fan ECC. Fuse 19 (15 amp) is for the ECC, door mirrors, rear wash/wipe, power seats and the cigar lighter.

I am wondering if you are both experiencing bad electrical contacts in the ignition switch which can play havoc with the electrics.

On both cars the SRS light should behave as in the attached:

700 SRS warning light..pdf: (73.74 KiB) Downloaded 911 times

It is possible to do a self diagnosis on the SRS system without special tools - well nearly without special tools - you will need a length of wire and 2 spade connectors.

700 SRS diagnosis and testing1..pdf: (1.05 MiB) Downloaded 745 times

700 SRS diagnosis and testing2..pdf: (1.15 MiB) Downloaded 695 times

700 SRS fault codes2..pdf: (1.31 MiB) Downloaded 640 times

If you do these checks take heed of the warnings. They can be done by enterprising home mechanics, which does include both of you!

Bill.

DeRail · Post by **DeRail** » 17 Apr 2009, 15:32

Let me rig up one of these bad boys and see what I get...

Will this diagnostic work if the SRS light goes out in the middle of my drive? In other words, is the crash sensor able to clear the code while driving? Had to go out again a little while ago and the light came back on. It sounded like the amp dropped for a split second, there was some sort of tick from the console area (could have been vent flaps I suppose) and the light disappeared and didn't come on the rest of the way home.

Thinking about it, I've owned the car over a year and it still has the fuses that came with it. I'm probably going to replace them, and run some contact cleaner in the fusebox.

Let me see what I can dig up,
Thanks!
Darrell

Post by **billofdurham** » 17 Apr 2009, 16:09

The crash sensor shouldn't clear the codes or else it has wasted its time storing them.

Bill.

DeRail · Post by **DeRail** » 17 Apr 2009, 17:05

billofdurham wrote:The crash sensor shouldn't clear the codes or else it has wasted its time storing them.

Bill.

Very true,

I gave the SRS test a whirl. I got slightly different results than what is posted from your workshop manual (I'm assuming thats where it's from?) I did not get a light after removing the wire from the cig lighter housing, however, a few seconds after removing the wire, a single light flashes. From your table, this would indicate a "Fault in crash sensor".

Hopefully Mr.crash sensor hasn't given up the ghost
Where does that live in the car, anyway, so that I can check connections, etc.?

Thanks!
Darrell

Post by **billofdurham** » 18 Apr 2009, 12:01

Mr. Crash Sensor is lurking in the dark under the driver's seat. He only awakens when the driver upsets him.

Work on the SRS needs a delicate touch and there are several dos and don'ts that need to be observed. I post this as a warning:

700 SRS service.pdf: (1.77 MiB) Downloaded 589 times

Bill.

DeRail · Post by **DeRail** » 18 Apr 2009, 12:20

Bill, thanks for the tips... I'm guessing that ensuring "all connections are tight" as indicated by the 1 flash of the SRS light, must be done at the yellow and orange connectors? Initially, I was thinking of reseating connector on crash sensor, but as I read in your pdf, THIS SHOULD NOT BE DONE. Or, is it that reseating the harness can only be done after disconnecting the orange and yellow wires? And is reseating the harness on the sensor the usual culprit in this case?

You also mentioned an ignition electrical short, is there any good way for diagnosing this?

Sorry for all the questions, I just want to be safe, and others reading this as well.

GSmith · Post by **GSmith** » 18 Apr 2009, 13:12

My SRS light has stayed off today so far - I've noticed in my one week of ownership of the car that it's possible to turn the ignition key too far when starting and it doesn't spring back to run position (this causes the starter to remain engaged until you manually turn the key back). I'm thinking that mine is all electrical with the ignition.

Anyone else ever have that problem?

Post by **billofdurham** » 18 Apr 2009, 15:49

Or, is it that reseating the harness can only be done after disconnecting the orange and yellow wires?

Before doing any work at the crash sensor you must disconnect and shield the battery negative cable. To shield it wrap it in non-conductive material and move it as far from the battery terminal as possible. At this point go and get a cup of coffee or whatever your preferred beverage is and take 5 - 10 minutes to drink it. Now disconnect the orange and yellow connectors and check the harness for security at the crash sensor. Now proceed as in the .pdf.

You also mentioned an ignition electrical short, is there any good way for diagnosing this?

It isn't so much a short as wear in the electrical portion of the switch which intermittently makes some items 'miss out' on the power. There really is no way of diagnosing this but next time you have problems with the fan, or anything else that should have kicked in at start up, try wiggling the key to see if the missing units come to life. If they do there is a problem with the electrical part of the switch. They are easy to change and are readily available.

I've noticed in my one week of ownership of the car that it's possible to turn the ignition key too far when starting and it doesn't spring back to run position

Try a small squirt of oil in the ignition lock which is the most used and least lubricated lock on the car. It may be that the moving parts in the lock itself are sticking. I always use a silicone based oil for locks.

Bill.