If it is any consolation we have had similar problems with our 99 V70 AWD. In our case the same symptoms you describe were diagnosed for me as a transmission problem, although we have had the oxygen sensor replaced twice as well. Keep in mind also that except when the "ABS" indicator is on the car drives normally and does not seem ready to stall, explode or spontaneously combust. When certain indicators come on the car does drive sluggishly.

I was told that a speedometer/odometer failing to work, ABS light, brake light, etc were the result of sensors within the transmission failing. So we have had extensive trans work done (at 70,000 miles) but are still experiencing problems.

Best of luck.

Had a lot of similiar problems with my 99v70. Finally fixed them all with an '04 Subaru Outback. Totally reliable, just as versatile. Much cheaper to own and operate. Never, not for a second have I missed the v70 and its totally ridiculous problems. If Volvo had any pride in workmanship they would buy back every one and destroy them.
My 96 850 is ten times the car the v70 will ever be.
Amen

Autozone will let you use an OBDII reader for free. Stores multiple codes and will clear the codes. At least you can then use the code and the internet to get a better understanding of the problem.

Thank you all for your help. Unfortuntely, I'm at the mechanics mercy. I also have a small leak from under the car near the passenger front seat side. It looks like antifreeze (???). It looks like the problem(s) could be a number of things- bad O2 sensor was replaced in the rear. Electrical problem? I'm wondering why some of those lights have appeared about three times in three weeks. Why would the odormeter reading disappear during that time (too bad it didn't lower the miles when it came back on!) Would you please clarify something for me - when the car is hooked up to the OBDII (or whatever you call it) what must be done to get the fault codes? Mechanic showed me the last time the rear O2 sensor bad. How are these codes cleared? Do you get a number of codes if there is more than one thing wrong? Do you get false results? I'm a single mom on a very limited budget and can't afford a new car......

jda2000 hit it right on the head.

You have at least two different problems.
You may want to start with the one that costs the least amount of money and that may have an effect on the other ones.
The ABS Control Unit.

Most likely your ABS Control Unit has failed. All of them will eventually fail after they reach 80,000 miles or 5 years.
Reading the ABS codes costs about $125.00 at the dealer and about 95% of the time, the diagnosis is a defective ABS Control Unit.

Here's information I have on this subject.
Vitor's ABS Web page
Click on the ABS / TRACS Link

there's a possibility the wrong sensor(s) were installed. happens alot, inside and outside the dealer. there's a bulletin detailing the new numbers and why they need to be done in pairs. the o2s breathe through the wiring itself to pick up reference oxygen and the new sensors do the job themselves or need an adapter harness, the bulletin details why or why not. good luck, chuck.

Stop throwing money away with replacing electrical components, get involved with the repairs of your car, or you'll waste tons of money. With the help of this board you'll be pointed in the right direction, even if you don't do the repairs yourself.

Buy yourself an OBDII reader so you can read your own codes. Very unlikely for both O2 sensors to go bad, most likely a leaking vaccuum elbow, the other one that was not fixed.

ABS/TRACS light indicates you have a bad ABS module, common failure in your car. About $130 to have it fixed. Do a search on ABS module failures on this board.

It's your car still under warranty. If it is you're in luck. The ETS light on, indicates an ETS module failure, another common failure in your car. About $1200 repair at the dealer. The ETS module failure will give hesitation, stalling, no start problems and a CEL light on. The ABS module failure will not give you a CEL light on, you just don't have anti-lock brakes.
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'88 240, '92 745, '98 v70 John, Tampa Bay

I dont know what fault codes that were stored,but it sounds like the A.B.S. control module has an intermittant fault in it.That part sends the vehicle speed signal to all of the control modules that need it.If the vehicle speed signal is lost,the upshift arrow can come on because the T.C.M. needs that signal.There can also be codes stored in the engine control module because of this.