My warning lights (brakes, ABS, transmission mode arrow, traction control, and check engine light) come on periodically. Not all at once, but between one and three at a time. Sometimes when they are on, the speedometer drops to zero and then mysteriously comes back on. Turning off the car will sometimes correct the warning lights being on. Some times they just go off by themselves. Once in a while it causes the acceleration to bog down. Occasionally, everything is fine and there are no warning lights on. Any ideas on what it might be?

Hawk,

I had similar issues with my 1998 S70 T5. Initially, the dealer tried to reset it assuming that it was a computer glitch.

I went to a certified Volvo mechanic and after he drove it, we found out that the issue was genuine. The culprit was the air pump and the ABS module. Not cheap though but my service was cheaper than going to Volvo dealer.

You ought to have it checked. It could be the ABS module or something more serious. He did tell me that if the ABS module is left like that for a long time, the odometer might mess up.

true, in some cases if its left alone too long it can mess up the odometer. sometimes the ABS pump( thing the module is bolted to) can leak causing the module to fail. doesnt happen very often but when it does, it can be pretty expensive.

Hawk, I'm a Service Advisor at a west coast Volvo dealer and I can tell you that 9.5 times out of 10 that is a Brake Control Module. The speedo drops out because the wheel speed sensor info is routed through that module to the speedo.

Most people call it the ABS computer. This will cause all of the lights mentioned to come on and all of the problems to happen. Go to a shop and have them pull codes for you there should be a perm. code in one of those modules.