Removal (Federal)

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: The Intake Air Heater (IAH) relay is inside of the glow plug controller on vehicles equipped with federal emissions.

Disconnect the negative battery cables. Loosen the outlet duct clamp at the upper intake manifold. Remove the upper intake manifold cover from the outlet duct. Remove the upper intake manifold cover.
Using a flat bladed screwdriver, disengage the glow plug controller cover clips. Remove the glow plug controller cover. See Figure. Remove the glow plug controller nuts. Lift the glow plug controller off the studs.
Separate the IAH relay from the glow plug controller housing by inserting a small screwdriver between them while prying the relay assembly outward. See Fig 1. Slide the IAH relay outward to disengage it from the glow plug controller housing.
Using a flat bladed screwdriver, disengage the IAH relay clip. Remove the IAH relay.

Fig 1: Separating Glow Plug Or Intake Air Heater Relay Assembly (Federal)

Courtesy of GENERAL MOTORS CORP.