It does not read the cat heating up.. the delay shift is there for the purpose of HEATING the cat as rapidly as possible if the collant temp is low.

The code is monitored by the rpm and ECT sensor.

If one were to warm the car first or hold the car in lower gear for first start, the code will never come on regarldess of the vac element being bad b/c the delay SOV signal will not be called for by the ECU....
..which is why guys 'BB" the SOV feed vac line.....

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A Dalton