Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
It is on the front frame rail, left side. Here is a picture of it. P0410 code?
Not too bad, (about one hour) but you will want to get the pump from the dealer as well as the hose kit for it. There has been a service bulletin for that. Let me give it to you.
Bulletin No.: 02-06-04-024G
Date: June 05, 2006
with 3.5L V6, 4.0L or 4.6L V8 Engine (VINs H, C, Y, 9 - RPOs LX5, L47, LD8, L37)
This bulletin is being revised to update the model year for Cadillac DeVille, parts usage information and enhance the bulletin content. Please discard Corporate Bulletin Number 02-06-04-024F (Section 6 - Engine).
Some customers may comment on the "Service Engine Soon" (U.S.) or "Check Engine Soon" (Canada) malfunction indicator lamp (MIL) being illuminated. Technicians may find these additional conditions:
This condition may be due to water being ingested at the secondary air injection reaction (AIR) pump inlet hose, causing the pump to short out or seize up.
Refer to SI for diagnostic information on DTC P0410.
If the diagnostic information above indicates a faulty AIR pump, follow the correction procedure below.
Aurora and DeVille
Install the new Secondary Air Injection Pump Outlet Pipe/Hose Assembly to the new Air Pump before installing to the vehicle. This will allow the housing on the hose/pipe assembly to fasten to the pump without damage to one of the holding fasteners.
Route the new AIR pump inlet hose between the left inner and out fenders as shown above.
Note: Secure the new AIR pump inlet hose and filter into the opening on the inner fender as shown above. If the filter is not properly secure to the inner fender repeat Non-Function Air pump may occur from ingesting water.
Note: A new Secondary AIR Pump and Inlet Hose Assembly (Kit), P/N 19515548 (2001-2003 SLS/STS) and 19515549 (2004 SLS or STS only), is now available and must be installed if the AIR pump is replaced. Non replacement and rerouting of the AIR pump Inlet hose when servicing the AIR pump may result in a repeat Non-Function AIR pump from ingesting water.
Note: It is critical that the new AIR inlet hose filter opening is facing downward when installed on the vehicle. If improperly installed Non-Function AIR pump may occur due to ingesting water into the pump.
Note: A new Secondary AIR Pump, P/N 25770944, and Inlet AIR Pump Filter Kit, P/N 15783306, are now available and must be installed if the AIR pump is replaced. Non-replacement and re-routing of the AIR pump Inlet hose and filter when servicing the AIR pump may result in a repeat non4unction AIR pump from water ingestion.