I keep getting this check engine code about once a week. I've checked all the lists of codes I can find online and it's never listed. Any idea what this is, it always happens 10-12 minutes into my drive and only in the morning

 

Since your sig has zero information, I assume your car is 2001+ with that code. It is for the A.I.R. system.

**edit** looks like 2004 only...

 

DTC P0491 or P0492
Circuit Description
The secondary air injection (AIR) pump system is designed to lower exhaust emission levels on a start up. The AIR pump is timed to remain ON for approximately 1 minute or until Closed Loop is achieved.

The powertrain control module (PCM) commands the AIR pump relay ON by supplying a ground to the AIR pump relay control circuit. This action energizes the AIR pump, forcing fresh air into the exhaust stream. The PCM also commands the AIR solenoid ON which applies engine vacuum to the AIR shut-off valve. With vacuum applied to the AIR shut-off valve, airflow from the AIR pump flows through the pipes/hoses to the exhaust check valves, then enters into the exhaust stream. The air, oxygen, that is introduced into the exhaust system accelerates catalyst operation. When inactive, the check exhaust valves and the shut-off valve prevent air flow in either direction.

The PCM detects a system air flow condition by monitoring the heated oxygen sensors (HO2S) and Short Term Fuel Trim during normal Open Loop AIR system operation. This is a passive test. If the passive test indicates a pass, the PCM takes no further action. If the passive test fails or is inconclusive, the diagnostic will proceed with an intrusive or active test. The PCM will command the AIR system ON during Closed Loop operation under normal operating conditions. The active test will pass or fail based on the response from the HO2S. A lean HO2S response indicates that the AIR system is functioning normally. An increasing Short Term Fuel Trim value also indicates a normal functioning system. The AIR diagnostic consists of the passive test and the active tests. The AIR diagnostic requires failure of the passive and active tests on 2 consecutive key cycles to illuminate the malfunction indicator lamp (MIL) and stores a DTC. If the PCM detects that the HO2S and Short Term Fuel Trim did not respond as expected on one of the engine banks, DTC P0491 for bank 1 or DTC P0492 for bank 2 sets.

 

Wow, thanks for the info. I really don't know all that much about it, but I'm learning. What am I suppose to get fixed?

 

I never saw a resolution to this. Detailed message on why but not how/what to fix. Any further info out there?

 

There was a thread on here several months ago, complete with pictures. The gist of what I recall is removing a couple of hoses and cleaning with some carb cleaner.
I have the same code - hoping to find the info again.

 

Is this the thread you're thinking about?
http://forums.corvetteforum.com/c5-t...eck-valve.html

 

Yes thank you very much

 

This forum is awesome. A little carb cleaner , w d 40 and air and its's a go. I don't know how anybody owns a vette with out getting help from this website (other than give GM dealers the farm). My experience with owning 2 vette is that they are about like helicopters, work on them for 8 hrs for every hour you drive them

 

I TO HAVE THIS FAILURE. I PURCHASED AUTO ENGINUITY SO I COULD GET A BETTER UNDERSTANDING OF WHAT MIGHT BE GOING ON. SO FAR I OBSERVED THE PASSANGER BANK 02 SENSOR DOES NOT READ ANY OXYGEN DURING STARTUP WHERE THE DRIVERS SIDE DID. KNOWING THE DRIVER SIDE IS OK ELIMINATES THE AIR PUMP. SO TRYING TO CHECK THE SECONDARY CHECK VALVE MIGHT BE EASER THAN JUST REPLACEING 02 SENSOR. I WAS ABLE TO REMOVE THE HOSE BEHIND THE ENGINE BLOCK. YES TIGHT. TRIED TO REMOVE IT BUT IT WAS ON WAY TO TIGHT. BEEN ON FOR 10 YRS. SPRAYED OIL BUT I KNOW THATS NOT THE SOLUTION. THE DRIVERS SIDE WAS LEAKING JUST A LITTLE. GOOD TIME TO REPLACE BOTH. DISCONNECTED PASSENGER EXHAUST TUBE AND WAS ABLE TO MAKE A HOSE TO FIT ON THE END OF THE VALVE. BARELY WAS ABLE TO GET ANY AIR FLOW THROUGH IT. SO THIS CONFIRMED THE LOW AIR FAILURE FOR ME. ITS ONLY THE INTAKE REMOVAL TO DO SO THATS WHERE ILL BE GOING. I HOPE THIS SHEADS MORE LIGHT ON THE SUBJECT FOR U

 

i read the forum notes about this issue , (after failing Maryland Exhaust Emissions Inspection, or more accurately I have dual PLX OBD 2 monitors and I reset the Check Engine Light before Inspection, , anyway the Inspection Computer would not set up because they thought the battery had been disconnected recently, so they told me drive around for 2 weeks and come back. I knew that wasn't going to change anything because the issue was still present. So I did exactly like the forum said i.e. Disconnect the driver side rulbber tubing and spray a good amount of Carb cleaner towards the tubing that leads behind the heads to the passenger side then used a compressed air blast or 3 to get the Carb Cleaner moved down the tubing then did the Sam with a few blasts of WD40 followed by compressed air blasts. Then put the system back together. I drove a bit that day and then a few more outings and the Check Engine light didn't come back on. Went to a Emissions Inspection today and ... PASSED , thank God , 2 more years of 810HP C5 Z06 cruising 👍 , this forum is wonderful. I have gotten many great clues and info just with a quick forum search. Thank you very much.
Paul Matera, MD 2004 C5 Z06 , supercharged/nitrous injected 810 HP DAILY DRIVER named SALLY