I've had this happen to me several times and the fault code is for the Pulsed Secondary Air Injection system. I believe the system only runs a full test when the ECU thinks it will not actually be used. Most times mine came on out on the highway after I had been traveling for about 10 minutes at speeds over 50 or so and the engine and CAT were fully warmed up. My short 10 minute/6 mile commute to work didn't usually activate the Check Engine Light.

First time was a rotted control line connector at the Air check Valve, (Side of engine with hose from pump and control line over the top of the engine.)

Another time self induced by me moving hoses around on the driver's side by the solenoid valve.

Last time I needed a new check valve. (Pump could't deliver any air because the valve wasn't opening.) When you present a small vacuum to the control port you should actuate the vlave and not be able to pull air through the port. You can test this by just sucking on it with your mouth. (You'll get a little nasty condensation if it is bad from the vacuum pulling exhaust into the top chamber and the control line.) When the pump runs and the valve opens you can feel a real vacuum at the inlet to the Air pump. When it is bad you only feel pulsing with no real vacuum there.

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'96 965, 16' wheels, Michelin Pilot Sports, rear 18mm bar + Koni, 201 HP cams, 133K. Put 200K on '85 745 TD.

The operation of the the air injection system occurs for about a minute and a half right after starting a cold engine. It pumps air into the exhaust system to start up the chemical reation in the cat a bit faster, then it shuts off never to be used again until the next cold start. But....the system gets tested occasionally during driving when you are at idle (if the idle period is long enough) the pump starts up and the ECU checks the O2 sensor(s) to see if there is a change in O2 content. If the idle period is too short the test will abort to be done later. I believe the 410 code is set when it fails to detect this change in O2 content. I think the most likely cause is the vacume supply to injection valve. Check the vacume lines and elbows from the solonoid valve on left fender to the injection valve on the exhaust side. Also check the vacume supply to the solonoid valve. You can also check for presence of vacume at the valve by pulling off the vacume line during the time the air pump is running after start up. All the above assumes the air pump is starting up OK and I think it is otherwise there would be a different code.
I am not sure if CEL comes on as soon as the initial fault is detected. It may take several reoccuring failures before it decides something is wrong.
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David Hunter