Well - I found the following from TSB 05.1-04.
ISSUE:The CHECK ENGINE MIL illuminates with no loss of power on 1995 MY vehicles within the VIN ranges listed below. Diagnosis with PDU indicates that DTC P0411 is stored in memory.At the end of the secondary air injection cycle, vacuum may become trapped in the hose from the air pump (AIRP) to the secondary air injection check valve (AIRC). The trapped vacuum will not allow the AIRP solenoid operated stop valve (integral with the AIRP) to open during the next air injection cycle. The ECM monitors no drift in the HO2S swings, which triggers the CHECK EN-GINE MIL.A revised air pump hose with a vacuum bleed is fitted to all AJ16 engines in production from VIN 734673 (Sedan [4.0L] Range).
Can someone with a US model take a look at the hose and see if it has a bleed nipple on it? I am not getting a code so I’m not experiencing this problem. Clearly if the valve is leaking there can be no trapped vacuum. But perhaps there will be when I change the valve?
I bought a NOS valve off Ebay for $44. I could not identify the GM version if in fact it exists. I’m suspecting it’s may be an SMP AV56.