P0420 and p0172
Thread Starter
Joined: 03-04-2017
Posts: 2
From: LA
P0420 and p0172
My friend bought a car from a carlot and sometimes on start up it would smoke from the back. Pulled up codes p0420 and p0172 when I open oil cap is smiling from crankcase. Now she just called me back and says car won't start. It's didn't run hot. Temperature was fine when I monitored it. Any help on fixing this would be appreciated. Thanks in advance
Platinum Member
Joined: 04-09-2006
Posts: 7,043
From: Vancouver, BC, Canada
Posting the year, mileage and engine would really help.
The code breakdown from https://www.chevyhhr.net/forums/prob...010-hhr-14259/ is as follows:
P0420 Catalyst System Low Efficiency
P0172 Fuel Trim System Rich
the p0420 is likely a result of the p0172. Check this page for diagnosing the p0172:
https://www.obd-codes.com/p0172
My first step would be to clean the MAF sensor using proper MAF Cleaner (not the cleaners the above link mentions). Here is a video that might help
the MAF is located on the intake tube just above the throttle body, and is easily accessed and removed for cleaning. Just to not touch the internal parts with your hands and make sure you reconnect it properly.
The code breakdown from https://www.chevyhhr.net/forums/prob...010-hhr-14259/ is as follows:
P0420 Catalyst System Low Efficiency
P0172 Fuel Trim System Rich
the p0420 is likely a result of the p0172. Check this page for diagnosing the p0172:
https://www.obd-codes.com/p0172
My first step would be to clean the MAF sensor using proper MAF Cleaner (not the cleaners the above link mentions). Here is a video that might help
the MAF is located on the intake tube just above the throttle body, and is easily accessed and removed for cleaning. Just to not touch the internal parts with your hands and make sure you reconnect it properly.
Platinum Member
Joined: 04-09-2006
Posts: 7,043
From: Vancouver, BC, Canada
some of the other items the OBD link suggests, can also be done easily at the same time:
•Inspect all vacuum and PCV hoses, replace if necessary
•Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
•Inspect fuel lines for cracks, leaks, or pinches
•Check the fuel pressure at the fuel rail
•Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
•Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)
•Inspect all vacuum and PCV hoses, replace if necessary
•Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
•Inspect fuel lines for cracks, leaks, or pinches
•Check the fuel pressure at the fuel rail
•Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
•Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)
Thread Starter
Joined: 03-04-2017
Posts: 2
From: LA
some of the other items the OBD link suggests, can also be done easily at the same time:
•Inspect all vacuum and PCV hoses, replace if necessary
•Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
•Inspect fuel lines for cracks, leaks, or pinches
•Check the fuel pressure at the fuel rail
•Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
•Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)
•Inspect all vacuum and PCV hoses, replace if necessary
•Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
•Inspect fuel lines for cracks, leaks, or pinches
•Check the fuel pressure at the fuel rail
•Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
•Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)
Administrator
Joined: 10-13-2011
Posts: 40,082
From: Welland,Ont Canada
P0172 is mostly caused by an exhaust leak ahead of the 1st O2 sensor, like a cracked or broken flex pipe.
P0420 is most likely related to that issue , it is the 2nd O2 sensor setting that code , it might be oil and condensation sucks into the intake and gumming up the catalytic converter.
P0420 is most likely related to that issue , it is the 2nd O2 sensor setting that code , it might be oil and condensation sucks into the intake and gumming up the catalytic converter.
Moderator
Joined: 01-23-2009
Posts: 26,532
From: Fredericksburg,VA
90% of the time the P0420 does mean a bad catalytic converter. You may be the lucky one.
However fix the P0172 first.
What did auto correct correct? Smoking?
Excessive burning of oil is the leading cause of dead catalytic converters. Can also cause a fouled MAF, which could case the P0172.
However fix the P0172 first.
What did auto correct correct? Smoking?
Excessive burning of oil is the leading cause of dead catalytic converters. Can also cause a fouled MAF, which could case the P0172.
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