'96 850 check engine AFTER air pump replacement?!

Here is the situation with my '96 850 wagon, 5sp:

Check Engine light came on.

Local Volvo mechanic said they read the code and the air pump has gone
bad. Said the car is fine to drive, but I would have to replace air
pump a few weeks before the emissions test to give the computer time to
clear all the codes. They reset the check engine light.

After a few weeks it came on again.

Had the airpump replaced for about $500 (d'oh!) right before long road
trip.

During trip (a few days later) the check engine light came on AGAIN!

I'd hate to think I spent that kind of money and the problem isn't
fixed! I have noticed that my exhaust pipe seems bigger (has a tip?)
and is angled downward more than other 850 wagons around town.

**Any ideas/comments?**
If not the air pump, what else could it be?
Any chance the mechanic can put my old air pump in and refund some of
the $500?

 

Sometimes repairs that change the operating conditions will turn the check
engine light on for a while until the ECU relearns how to work. I had that
happen on my company truck after it had its first tune-up... at 150K miles!
Time to take it back to the mechanic to see what codes are showing up now.
In the meantime, it's safe to keep driving as long as you don't do any hard
prolonged acceleration, like charging up long hills on the freeway.

Mike

 

The air pump is a system, consisting of a solenoid valve, shut off
valve, air pump, relay, vacuum hoses and air hoses. If the shutoff
valve is seized or not receiving vacuum because of a solenoid valve or
vacuum hose problem, or the relay doesn't work, or the fuse is dead,
then the light will come back on.
More info: http://www.volvospeed.com/Repair/airpump1.htm

And of course the light may be on for a totally different reason.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

That is EXACTLY what happened. I took it back and they said the
solenoid was bad and it cost around $70 to replace that. Now the car
drives well and no check engine light.

-Atif