Code po492hc
Thread Starter
Intermediate
Joined: Jul 2004
Posts: 33
Likes: 0
From: HOUSTON TX
Code po492hc
I can't find this code on list. What is it? I just started getting a check engine light that goes out on its own after 3 or 4 starts then it comes back on. Dealer wants me to bring it in and won't tell me what code means. Thanks.
Melting Slicks
Joined: Jun 2004
Posts: 3,439
Likes: 6
From: Newark, DE
St. Jude Donor '06
From the 2004 service manual:
HTH!
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.
MIL = check engine light; Bank 1 = driver side; bank 2 = passenger sideHTH!
Melting Slicks
Joined: Jun 2004
Posts: 3,439
Likes: 6
From: Newark, DE
St. Jude Donor '06
There are several possibilities.
Air is injected into the exhaust port via the fitting on the exhaust manifold, upstream through a check valve, and eventually back to the AIR pump. It's not unusual for the check valves to sieze or rust shut, especially on cars that see a lot of short distance driving, where the engine doesn't get a chance to fully come up to temp and burn out condensation. Check the easy stuff first. Trace the plumbing back and look for evidence of any kinked hoses, loose connections, missing clamps or audible leaks. The AIR pump normally only runs for a short period of time at cold engine start-up, so that would be the time to check for leaks. A piece of hose can be used as a stethescope to help you pinpoint location. If you don't find anything conclusive, your check valve may be frozen in positon. If you feel lucky, you can try spraying some anti-seize or WD-40 in the hose toward the valve. Really soak it, and then let it sit overnight. Clear the codes, then restart the car and see if it comes back. Remember that it takes two consecutive ignition cycles with a failure before the CEL comes on.
If you still have a problem at this point, it's probably best to have a professional look at it. It can become expensive if you just guess and start shotgunning parts.
GL!
- excessive exhaust back-pressure
- upstream air leak between the AIR pump and where it eventually plumbs into the exhaust manifold
- bad O2 sensor
Air is injected into the exhaust port via the fitting on the exhaust manifold, upstream through a check valve, and eventually back to the AIR pump. It's not unusual for the check valves to sieze or rust shut, especially on cars that see a lot of short distance driving, where the engine doesn't get a chance to fully come up to temp and burn out condensation. Check the easy stuff first. Trace the plumbing back and look for evidence of any kinked hoses, loose connections, missing clamps or audible leaks. The AIR pump normally only runs for a short period of time at cold engine start-up, so that would be the time to check for leaks. A piece of hose can be used as a stethescope to help you pinpoint location. If you don't find anything conclusive, your check valve may be frozen in positon. If you feel lucky, you can try spraying some anti-seize or WD-40 in the hose toward the valve. Really soak it, and then let it sit overnight. Clear the codes, then restart the car and see if it comes back. Remember that it takes two consecutive ignition cycles with a failure before the CEL comes on.
If you still have a problem at this point, it's probably best to have a professional look at it. It can become expensive if you just guess and start shotgunning parts.
GL!
Burning Brakes
Joined: Dec 2003
Posts: 1,066
Likes: 9
From: Eddy Texas
There are several possibilities.
Air is injected into the exhaust port via the fitting on the exhaust manifold, upstream through a check valve, and eventually back to the AIR pump. It's not unusual for the check valves to sieze or rust shut, especially on cars that see a lot of short distance driving, where the engine doesn't get a chance to fully come up to temp and burn out condensation. Check the easy stuff first. Trace the plumbing back and look for evidence of any kinked hoses, loose connections, missing clamps or audible leaks. The AIR pump normally only runs for a short period of time at cold engine start-up, so that would be the time to check for leaks. A piece of hose can be used as a stethescope to help you pinpoint location. If you don't find anything conclusive, your check valve may be frozen in positon. If you feel lucky, you can try spraying some anti-seize or WD-40 in the hose toward the valve. Really soak it, and then let it sit overnight. Clear the codes, then restart the car and see if it comes back. Remember that it takes two consecutive ignition cycles with a failure before the CEL comes on.
If you still have a problem at this point, it's probably best to have a professional look at it. It can become expensive if you just guess and start shotgunning parts.
GL!
- excessive exhaust back-pressure
- upstream air leak between the AIR pump and where it eventually plumbs into the exhaust manifold
- bad O2 sensor
Air is injected into the exhaust port via the fitting on the exhaust manifold, upstream through a check valve, and eventually back to the AIR pump. It's not unusual for the check valves to sieze or rust shut, especially on cars that see a lot of short distance driving, where the engine doesn't get a chance to fully come up to temp and burn out condensation. Check the easy stuff first. Trace the plumbing back and look for evidence of any kinked hoses, loose connections, missing clamps or audible leaks. The AIR pump normally only runs for a short period of time at cold engine start-up, so that would be the time to check for leaks. A piece of hose can be used as a stethescope to help you pinpoint location. If you don't find anything conclusive, your check valve may be frozen in positon. If you feel lucky, you can try spraying some anti-seize or WD-40 in the hose toward the valve. Really soak it, and then let it sit overnight. Clear the codes, then restart the car and see if it comes back. Remember that it takes two consecutive ignition cycles with a failure before the CEL comes on.
If you still have a problem at this point, it's probably best to have a professional look at it. It can become expensive if you just guess and start shotgunning parts.
GL!
Had that code on my '04. It was a check valve. I have GMPP and my dealer just replaced both check valve for me.I would try cleaning them first.
Thread Starter
Intermediate
Joined: Jul 2004
Posts: 33
Likes: 0
From: HOUSTON TX
Burning Brakes
Joined: Dec 2003
Posts: 1,066
Likes: 9
From: Eddy Texas
If you don't find anything conclusive, your check valve may be frozen in positon. If you feel lucky, you can try spraying some anti-seize or WD-40 in the hose toward the valve. Really soak it, and then let it sit overnight. Clear the codes, then restart the car and see if it comes back. Remember that it takes two consecutive ignition cycles with a failure before the CEL comes on.
If you still have a problem at this point, it's probably best to have a professional look at it. It can become expensive if you just guess and start shotgunning parts.
GL!
If you still have a problem at this point, it's probably best to have a professional look at it. It can become expensive if you just guess and start shotgunning parts.
GL!
Sorry, don't have any pics to show the check valves, but there is one on each side. Pull the hose off and try to soak them. It' worth a try.
