QuestionHi Tino,
My question is related to the one you were asked on 11/19/2006 regarding codes P0491 and P0492.
I also had the service light on and the descriptions for the 2 codes were: Secondary Air Injection System Bnk1 and Bnk2.
Do you know what parts I need to have replaced (ie. Smog Pump or one of the 2 Oxygen Sensors at the manifold or the 2 Oxygen Sensors near the catalytic converter)? Since all of these parts are expensive, it would be nice to know that I don't have to replace everything.
Thanks very much.
AnswerHi Sanjeev,
Once you get fault codes, it does not automatically mean that you have to replace parts. The FC's simply mean that you have problems in the circuits mentioned(in your case the secondary air systems in banks 1 & 2). You still have to diagnose the cause of the problem before you replace parts if needed.
Sometimes you do not even need to replace anything(like when you just cut a vacuum hose with a loose end provided it still reaches its destination, or you just plug a connector that got loose).
Your problem is with the secondary air pump system(the system in general since it involves both banks). At cold engine startup, the pump runs for about a minute to provide extra air into the exhaust system so that unburned gases gets burned off in the catalytic converter as part of the emissions system.
The general overview of the system is this:
1) the pump is turned on by the engine computer (DME) at cold startup
2) the DME switches on the pump relay (usually found behind the glove box) which turns on the pump. The DME does its work properly when the 5 fuses in the main electronic box are not blown(the fuses are housed in a small box of 5 fuses). The small fuse box in turn is housed inside the big black box either on the left or right side of the engine compartment.
3) if the pump does not turn on at cold startup then there may not be power at the connector to the pump or the pump itself is bad (or the pump may turn slower due to low voltage supply or due to a bad pump motor); you can feel and hear the pump running it is at the right somewhat front area of the engine compartment
4) when running, the pump provides the air output thru a hose to a valve which is switched on by a vacuum switch solenoid (thru a small vacuum hose), usually the hose gets wornout and can no longer switch on the valve, sometimes the solenoid switch goes bad (this is at the left side rear end of the engine), sometimes the valve itself goes bad (you can test this by removing the valve, looking for free movement and functional testing by supplying vacuum to it)
5) when the valve is working properly, then the air supplied by the pump goes into the exhaust manifold and then the catalytic converter
6) the oxygen sensors before and after the catalytic converter monitors the situation during the brief span that the pump works (at cold startup) and then gives an OK or stores a fault as needed.
So you see, it is not a simple matter. But with the above data you can diagnose the problem and find out for yourself what the car needs. It can be a fuse, relay, valve, solenoid switch, vacuum hose, or pump. But definitely not 02 sensors.
Tino
