Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Help Secondary Air Injection P0491

Anyone familiar with this code? Looking this up it looks like an air pump. Anyone know where this is located on the dodge advenger? I just replaced my bulbs in my headlights and my check engine light. And on the next day?

It’s a 2010 Dodge Advenger 124k miles

You probably have a hose coming out of the air filter box. This hose should go to the air pump. Follow the hose…

Edit: Did you by chance have to remove the air filter box or attached hose(s) to get to the light bulbs? If yes, double check that the hoses are properly re-attached.

Here’s what the injector pump looks like.

The code indicates insufficient flow from the injector pump.

The first thing to check is item 6, injector pump inlet filter/check valve.


Secondary air is an electrically driven air pump that operates during the first two minutes of starting a cold engine. Right after start up, the computer sends extra fuel to the engine to keep it running while cold. The pump is turned on to inject extra air into the exhaust manifold to burn off the excess fuel. It also heats up the warm up catalytic converter really fast.

This is a two fault DTC (diagnostic trouble code) meaning it has to be detected twice in two consecutive drive cycles to turn on the check engine light (CEL or MIL). What the computer is actually monitoring is the O2 sensor. If the secondary air does not turn on or is blocked from the exhaust, the O2 sensor will read rich.

Since this just started after replacing your head lights and the secondary air pump is usually located behind or just under one of the head lights, I’d say you might have accidentally disconnected the wiring or removed a hose and not put it back. The pump itself is usually not the cause of the problem.