Undiagnosed Emergency

2001 Volvo V70 XC, 5cyl. 150K miles, just serviced and safety inspected, including replacement of Airbag System control unit. Excellent condition and performance, until…
Undiagnosed night emergency – description:
Very cold weather. Nighttime – driving ~30mph in heavy-traffic on divided 4-lane.

  1. With no driver input, all exterior lighting went off – including headlights, parking, position, tail, brakes, and signals. No DRL or fog lights
  2. Managed to cross lanes to pull off out of traffic
  3. Parked on side of road, with engine and heater blower running – discovered that warning flashers still work on front/rear/side – and called to be picked up
  4. While waiting, I took inventory as follows:
    a. Systems OFF: all driving and position lights (see above), and audio system
    b. Systems ON: running engine, instrument panel, interior lighting, heater/blower, climate control panel, power seats, power locks, door chimes
    c. Warning lights/messages: “general warning” light, “check engine” light (was not on previously), and “Air Bag Service – URGENT” message
  5. My pick up arrived. I shut down engine, and then checked to see if it would restart. It did.
  6. All exterior lights and audio system came back on, but panel warning lights stayed on too.
  7. I then drove home without incident.

I now can’t be sure that driving is safe – either night or day (brake lights?) until this incident is diagnosed and corrected.
A mechanic I’ve respected for many years has tried for a week to test and diagnose the problem. No success.

Has your mechanic checked the alternator’s output?
When the diodes in an alternator are failing, it is not unusual to have very quirky electrical/electronic problems that may be transitory in nature.

All the circuits that went dead are controlled thru the Central Electronic Module.

If it happens again, I’d change the module.


If you had the airbag serviced it may be likely that the mechanic has loosened the connections leading into the under hood Fuse box… If he forgot to tighten those connections in that box you could see issues as you described. I would be looking for loose connections as a result of the Airbag swap…in order to prevent an accidental Airbag deploy the mechanic probably loosened some serious electrical connections to assure no deployment… Look into that fuse box under the hood and at all major electrical connections that are able to be loosened.


The first thing that I’d like to stress is…whenever a check engine light comes on…pull over, shut off the engine and check the oil. Because you had just had it serviced…the mechanic could have forgotten to tighten the oil drain causing you to lose all your oil. The short drive home then would have totally ruined your engine and you’d be paying 3,000 to 5,000 for a replacement.
Nothing else can do more harm to an engine than NO OIL!!!
If the oils good and the temp gauge is normal you may harm something, but it will not be catastrophic.

For your problem I’d think your mechanic has already checked…loose connectors, ground straps, and the back of the fuse panel looking for burn marks.

What codes did the mechanic find in the computer when he scanned it???


I like @Tester’s comment about the CEM module but I would check for a power input problem with it. Since things are working again it appears to be an intermittent problem like a bad wire connection would cause.