2009 chevy express 2500 code p0171
December 19th, 2023, 12:18 PM
#31
December 19th, 2023, 3:53 PM
#32
If your goal is to pass emissions testing, then I don't think they're going to look kindly on it, and you'll probably get a fine in the thousands of dollars, since modifying emissions systems is against federal law.
December 20th, 2023, 11:43 AM
#33
CF Veteran
This screen indicates the drive cycle monitors that have completed or not completed. The ones highlighted in green with a check mark are the ones that have completed - the ones in gray with the “cut circle” are monitors that do not apply - the ones in orange with an X are the monitors that have not completed yet.
Generally speaking, EVAP system monitors require at least 2 drive cycles to complete. This is because the PCM has to monitor the fuel tank pressure after shut down for a given amount of time before it can assess the integrity of the EVAP system.
Drive the van as you normally would for 2 days and then recheck the EVAP monitor status.
Most Monitors will reset and require drive cycles with every battery disconnect.
In most cases, no. The O2 sensors only report the amount of oxygen in the exhaust stream and are rarely the cause of these codes.
Possible causes include:
1) Intake vacuum leaks. Verify all external vacuum hoses/components aren’t leaking. The easiest way to do this is to warm the engine up to temperature, observe the short term fuel trim (STFT) at idle, then disconnect and plug all external vacuum ports on the manifold and recheck STFT. If external hoses/components are OK, there will be no noticeable change in the STFT - however if one or more component is leaking, the STFT will decrease relative to its original reading (example - with all vacuum connections in place, STFT may read +15% - but with them all disconnected and plugged, it reads less than +5%).
If there’s no change with disconnecting the vacuum hoses, monitor STFT while spraying carb cleaner around the intake manifold gaskets. If the gasket is leaking, STFT will momentarily go negative (example - STFT changes from +15% to -10%). Replace the intake gaskets, including the TB, and check for cracks in the intake manifold while it’s off.
2) Leaks at the exhaust manifolds and/or manifold to pipe flanges. Broken exhaust manifold bolts are a very common problem on these engines. If it’s not audible, a visual inspection is usually enough to see which bolts are broken as the heads will be missing. If the bolts are all in place, looks for soot tracking around the head to manifold ports (heat shield removal may be needed).
3) A worn fuel pump or fuel supply restriction causing low pressure and/or volume. Pressure should be 50-60 PSI key on engine off and hold for at least a few minutes - it should maintain approximately 55 PSI with the engine running. The pump should be able to flow at least 1 pint in 30 seconds to provide adequate volume. If pressure or volume is low, replace the pump, inline filter (if equipped) and flush the fuel lines with compressed air.
Generally speaking, EVAP system monitors require at least 2 drive cycles to complete. This is because the PCM has to monitor the fuel tank pressure after shut down for a given amount of time before it can assess the integrity of the EVAP system.
Drive the van as you normally would for 2 days and then recheck the EVAP monitor status.
Most Monitors will reset and require drive cycles with every battery disconnect.
Possible causes include:
1) Intake vacuum leaks. Verify all external vacuum hoses/components aren’t leaking. The easiest way to do this is to warm the engine up to temperature, observe the short term fuel trim (STFT) at idle, then disconnect and plug all external vacuum ports on the manifold and recheck STFT. If external hoses/components are OK, there will be no noticeable change in the STFT - however if one or more component is leaking, the STFT will decrease relative to its original reading (example - with all vacuum connections in place, STFT may read +15% - but with them all disconnected and plugged, it reads less than +5%).
If there’s no change with disconnecting the vacuum hoses, monitor STFT while spraying carb cleaner around the intake manifold gaskets. If the gasket is leaking, STFT will momentarily go negative (example - STFT changes from +15% to -10%). Replace the intake gaskets, including the TB, and check for cracks in the intake manifold while it’s off.
2) Leaks at the exhaust manifolds and/or manifold to pipe flanges. Broken exhaust manifold bolts are a very common problem on these engines. If it’s not audible, a visual inspection is usually enough to see which bolts are broken as the heads will be missing. If the bolts are all in place, looks for soot tracking around the head to manifold ports (heat shield removal may be needed).
3) A worn fuel pump or fuel supply restriction causing low pressure and/or volume. Pressure should be 50-60 PSI key on engine off and hold for at least a few minutes - it should maintain approximately 55 PSI with the engine running. The pump should be able to flow at least 1 pint in 30 seconds to provide adequate volume. If pressure or volume is low, replace the pump, inline filter (if equipped) and flush the fuel lines with compressed air.
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mountainmanjoe (December 20th, 2023)
December 20th, 2023, 4:24 PM
#34
I install the spacers on the o2 sensors let's see if the codes p0171 and p0174 goes away if it doesn't then I'm screwed
December 20th, 2023, 6:52 PM
#35
This screen indicates the drive cycle monitors that have completed or not completed. The ones highlighted in green with a check mark are the ones that have completed - the ones in gray with the “cut circle” are monitors that do not apply - the ones in orange with an X are the monitors that have not completed yet.
Generally speaking, EVAP system monitors require at least 2 drive cycles to complete. This is because the PCM has to monitor the fuel tank pressure after shut down for a given amount of time before it can assess the integrity of the EVAP system.
Drive the van as you normally would for 2 days and then recheck the EVAP monitor status.
Most Monitors will reset and require drive cycles with every battery disconnect.
In most cases, no. The O2 sensors only report the amount of oxygen in the exhaust stream and are rarely the cause of these codes.
Possible causes include:
1) Intake vacuum leaks. Verify all external vacuum hoses/components aren’t leaking. The easiest way to do this is to warm the engine up to temperature, observe the short term fuel trim (STFT) at idle, then disconnect and plug all external vacuum ports on the manifold and recheck STFT. If external hoses/components are OK, there will be no noticeable change in the STFT - however if one or more component is leaking, the STFT will decrease relative to its original reading (example - with all vacuum connections in place, STFT may read +15% - but with them all disconnected and plugged, it reads less than +5%).
If there’s no change with disconnecting the vacuum hoses, monitor STFT while spraying carb cleaner around the intake manifold gaskets. If the gasket is leaking, STFT will momentarily go negative (example - STFT changes from +15% to -10%). Replace the intake gaskets, including the TB, and check for cracks in the intake manifold while it’s off.
2) Leaks at the exhaust manifolds and/or manifold to pipe flanges. Broken exhaust manifold bolts are a very common problem on these engines. If it’s not audible, a visual inspection is usually enough to see which bolts are broken as the heads will be missing. If the bolts are all in place, looks for soot tracking around the head to manifold ports (heat shield removal may be needed).
3) A worn fuel pump or fuel supply restriction causing low pressure and/or volume. Pressure should be 50-60 PSI key on engine off and hold for at least a few minutes - it should maintain approximately 55 PSI with the engine running. The pump should be able to flow at least 1 pint in 30 seconds to provide adequate volume. If pressure or volume is low, replace the pump, inline filter (if equipped) and flush the fuel lines with compressed air.
Generally speaking, EVAP system monitors require at least 2 drive cycles to complete. This is because the PCM has to monitor the fuel tank pressure after shut down for a given amount of time before it can assess the integrity of the EVAP system.
Drive the van as you normally would for 2 days and then recheck the EVAP monitor status.
Most Monitors will reset and require drive cycles with every battery disconnect.
In most cases, no. The O2 sensors only report the amount of oxygen in the exhaust stream and are rarely the cause of these codes.
Possible causes include:
1) Intake vacuum leaks. Verify all external vacuum hoses/components aren’t leaking. The easiest way to do this is to warm the engine up to temperature, observe the short term fuel trim (STFT) at idle, then disconnect and plug all external vacuum ports on the manifold and recheck STFT. If external hoses/components are OK, there will be no noticeable change in the STFT - however if one or more component is leaking, the STFT will decrease relative to its original reading (example - with all vacuum connections in place, STFT may read +15% - but with them all disconnected and plugged, it reads less than +5%).
If there’s no change with disconnecting the vacuum hoses, monitor STFT while spraying carb cleaner around the intake manifold gaskets. If the gasket is leaking, STFT will momentarily go negative (example - STFT changes from +15% to -10%). Replace the intake gaskets, including the TB, and check for cracks in the intake manifold while it’s off.
2) Leaks at the exhaust manifolds and/or manifold to pipe flanges. Broken exhaust manifold bolts are a very common problem on these engines. If it’s not audible, a visual inspection is usually enough to see which bolts are broken as the heads will be missing. If the bolts are all in place, looks for soot tracking around the head to manifold ports (heat shield removal may be needed).
3) A worn fuel pump or fuel supply restriction causing low pressure and/or volume. Pressure should be 50-60 PSI key on engine off and hold for at least a few minutes - it should maintain approximately 55 PSI with the engine running. The pump should be able to flow at least 1 pint in 30 seconds to provide adequate volume. If pressure or volume is low, replace the pump, inline filter (if equipped) and flush the fuel lines with compressed air.
December 20th, 2023, 7:46 PM
#36
CF Veteran
I’ve seen a few manifold bolts loosen up and fall out, but typically the heads break off and the shaft remains in the head.
Broken/missing exhaust bolts will only cause codes on the corresponding bank - if there’s no bolt problems on the other bank, the reason for lean codes on both banks is still likely an intake leak or fuel pressure issue.
December 21st, 2023, 11:18 AM
#38
December 21st, 2023, 12:02 PM
#39
CF Veteran
On these engines, intake and exhaust leaks are the most common problems, followed closely by weak fuel supply and/or incorrect fuel (E15 or higher ethanol blends when the engine isn’t rated for it).
If you want to resolve these codes, you need to methodically analyze the related components for proper operation to determine the cause. If you’re unable to do so, take the van to a shop you can trust.
Speaking for myself, I can help guide you through the diagnosis, but only if you’re willing to follow the advice/directions given, and at this point, you have tests that can be done to bring you closer to the answer. If there’s anything about my instructions you don’t understand, by all means, ask for clarification.
December 21st, 2023, 1:05 PM
#40
The new codes are set because the sensor element isn’t properly inserted into the exhaust stream and so it’s unable to function properly. O2 sensor spacers are intended for use on vehicles that have had the emissions controls deleted - they won’t solve any problems on stock systems.
On these engines, intake and exhaust leaks are the most common problems, followed closely by weak fuel supply and/or incorrect fuel (E15 or higher ethanol blends when the engine isn’t rated for it).
If you want to resolve these codes, you need to methodically analyze the related components for proper operation to determine the cause. If you’re unable to do so, take the van to a shop you can trust.
Speaking for myself, I can help guide you through the diagnosis, but only if you’re willing to follow the advice/directions given, and at this point, you have tests that can be done to bring you closer to the answer. If there’s anything about my instructions you don’t understand, by all means, ask for clarification.
On these engines, intake and exhaust leaks are the most common problems, followed closely by weak fuel supply and/or incorrect fuel (E15 or higher ethanol blends when the engine isn’t rated for it).
If you want to resolve these codes, you need to methodically analyze the related components for proper operation to determine the cause. If you’re unable to do so, take the van to a shop you can trust.
Speaking for myself, I can help guide you through the diagnosis, but only if you’re willing to follow the advice/directions given, and at this point, you have tests that can be done to bring you closer to the answer. If there’s anything about my instructions you don’t understand, by all means, ask for clarification.
The following users liked this post:
Triaged (December 21st, 2023)