Hope this helps.
I'd be sure they looked at the service bulletin:
#04-06-04-037: Check Engine Light On, DTC P0410 Set, Water in AIR Pump (Replace AIR Pump, Install New Hose and Shield) - (May 27, 2004)
Subject: Check Engine Light On, DTC P0410 Set, Water in AIR Pump (Replace AIR Pump, Install New Hose and Shield)
Models: 2000-2002 Buick Regal
2000-2002 Chevrolet Impala, Monte Carlo
2000-2002 Oldsmobile Intrigue
2000-2002 Pontiac Grand Prix
with 3.5L or 3.8L Engine (VINs H, K - RPOs LX5, L36)
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Condition
Some owners may comment on the check engine light being illuminated. Upon investigation, the technician may find a DTC P0410 indicating that there is a concern in the secondary air injection system. When removing the air pump, the technician may also note evidence of water intrusion in the secondary air injection pump.
Cause
Water may have collected in the AIR pump and frozen or corroded the pump.
Correction
Replace the Secondary Air Injection Pump and install a new hose, shield and cleaner using the following procedure:
Some more info:
Secondary Air Injection System Description
The secondary air injection (AIR) system helps reduce exhaust emissions. The system forces fresh filtered air into the exhaust stream in order to accelerate catalyst operation.
The system includes the following:
• AIR pump--The AIR pump supplies filtered air through the secondary air injection system into the exhaust stream. The control module provides ground for the pump relay. Battery voltage is then applied to the pump. The filter is the only serviceable part of the pump.
• AIR vacuum control solenoid--The AIR vacuum control solenoid controls the AIR shut-off valve. When the AIR system is enabled, the control module provides a ground to the solenoid. Enabling the solenoid, allows engine vacuum to be applied to the AIR shut-off valve.
• AIR shut-off valve--The AIR shut-off valve is vacuum operated. When the AIR system is enabled, vacuum is applied to the valve.
• Check valves--The check valves prevent back flow of exhaust gases into the AIR system.
• Plumbing--The plumbing carries the air from the pump to the exhaust stream. The plumbing includes the hoses, pipes and clamps. The plumbing can be tested for leaks using a soapy water solution. With the AIR pump running, bubbles will form if a leak exists.
Results of Incorrect Operation
If no air, or oxygen, flow enters the exhaust stream, the start up emission levels will rise. The control module can detect a system flow problem using the pre-catalyst heated oxygen sensor (HO2S) and short term fuel trim (FT). If a system flow problem is present the HO2S voltage will not indicate an expected lean condition, short term FT will not increase and a DTC will set.
If incorrect voltage is present on the vacuum control solenoid or the pump relay control circuits the device will not operate. This will be detected by the control module and a diagnostic trouble code (DTC) will set.
The following DTCs can set if a secondary air injection fault is detected:
• DTC P0410--A system flow problem has been detected.
• DTC P0412--A vacuum control solenoid control circuit problem has been detected.
• DTC P0418-- A pump relay control circuit problem has been detected.