1995 Volvo 940

Computer problem
1995 Volvo 940 4 cyl Two Wheel Drive Automatic 185000 miles

A steady check engine light is on, but the car suffers no performance issues. It has been on for about 4 months.

It did not come on until Volvo dealer repaired my non-functioning heater. Two days later the check engine light comes on. Took it back a couple of weeks later. EGR was replaced, the light came on 2 or 3 days later. After reading everything I could. I think the light came on a couple of days later is that the battery was disconnected and cleared the check engine light.

I have replaced various things such as air filter, spark plugs and wires and gas cap. Light is still on. I now want to take more control. I would like know how I can identify where the OBD 1 unit is located and what is looks like. Then I need to figure out how to use it. Any help appreciated.
April 23, 2009.

I thought the check engine light was just timed with the odometer or something - when it comes on I push the little button behind the rubber stopper in the instrument cluster (behind the clear plastic window where the speedometer etc. Live).

Jun 3, 2009.