P0171 and P0420 code problems
Senior Member
Joined: 03-29-2022
Posts: 1,240
From: Davison MI
i haven't had a chance to do anything with the HHR until after work today where i wanted to double check the fuel presure situation. So car has been sitting another week and this is what i did. Hooked up fuel gauge (really need to just buy one - they charge $160 at autozone to borrow one!)
Hooked up - gauge read about 32/34. Turned key on - stayed at that level... Decided to see if maybe it would start... Almost did... Presurre jumped to 58/60.... turned key off and watched gauge. Took about 5 min and slowly dropped down to 34.. from 58-50 was fairly quick... then much slower from 50 -34. Continued to monitor it for another 15 min and pressure stayed around 32/33. Is this the sign of a failing fuel pump?
Hooked up - gauge read about 32/34. Turned key on - stayed at that level... Decided to see if maybe it would start... Almost did... Presurre jumped to 58/60.... turned key off and watched gauge. Took about 5 min and slowly dropped down to 34.. from 58-50 was fairly quick... then much slower from 50 -34. Continued to monitor it for another 15 min and pressure stayed around 32/33. Is this the sign of a failing fuel pump?
Thread Starter
Senior Member
Joined: 08-09-2020
Posts: 118
From: tampa bay
i decided to recheck fuel pressure before returning the gauge yesterday and it went to 58~60 but still wouldn't turn over the engine.... shut it off and it stayed at about 55+. Tell me if I'm wrong, but wouldn't that indicate a different issue than the fuel pump? I think someone mentioned possibly bad/clogged fuel injectors? Could the starter be failing? I know part of my thinking is hopium in that the issue might be something topside that would allow me to fix the car while it is immobile and on the ground. It always seems that when you start replacing things on a neglected car (ie previously replaced ignition coil/ECM, sparkplugs, battery, etc), other things decide it's their turn to get attention and fail on you.
Moderator
Joined: 05-01-2014
Posts: 8,509
From: California
You're going to have to check your wording. Whether the engine "turns over" has nothing to do with fuel. I'm going to guess that you mean it cranks(which is turning over), but won't start.
But you've tested fuel pressure 3 times now, with 3 different results. I'm not sure which, if any, results are true. My understanding, you don't turn the key to "start" during the fuel pressure test. Perhaps this is what is causing such erratic results.
But you've tested fuel pressure 3 times now, with 3 different results. I'm not sure which, if any, results are true. My understanding, you don't turn the key to "start" during the fuel pressure test. Perhaps this is what is causing such erratic results.
Moderator
Joined: 01-23-2009
Posts: 26,484
From: Fredericksburg,VA
I am soooo confused.
What does the fuel pump have to do with the starter?
When did the car fail to start?
How can you have P0171 and P0420 when the motor is not running?
The fuel pump only runs for about 20 seconds if the motor does not start.
The fuel pump testing should be done key on motor off. You might need to cycle the key several times to get the pressure high.
P0171 rarely is a fuel pump problem. If there is a current P0420; the test does not run, the computer is in open loop; meaning that the #1 O2 sensor is not being used. The #1 O2 sensor controls the Air/Fuel mixture. P0171 is about how much correcting the computer is doing, not about how rich/lean the A/F mixture is.
Ignore any code marked "pending" or "historic" or "permanent"; the only ones that matter are "current".
The problem is the P0420 that you have been ignoring, it makes the ECM ignore any input from sensors and forces the computer to guess.
What does the fuel pump have to do with the starter?
When did the car fail to start?
How can you have P0171 and P0420 when the motor is not running?
The fuel pump only runs for about 20 seconds if the motor does not start.
The fuel pump testing should be done key on motor off. You might need to cycle the key several times to get the pressure high.
P0171 rarely is a fuel pump problem. If there is a current P0420; the test does not run, the computer is in open loop; meaning that the #1 O2 sensor is not being used. The #1 O2 sensor controls the Air/Fuel mixture. P0171 is about how much correcting the computer is doing, not about how rich/lean the A/F mixture is.
Ignore any code marked "pending" or "historic" or "permanent"; the only ones that matter are "current".
The problem is the P0420 that you have been ignoring, it makes the ECM ignore any input from sensors and forces the computer to guess.
Senior Member
Joined: 03-29-2022
Posts: 1,240
From: Davison MI
i decided to recheck fuel pressure before returning the gauge yesterday and it went to 58~60 but still wouldn't turn over the engine.... shut it off and it stayed at about 55+. Tell me if I'm wrong, but wouldn't that indicate a different issue than the fuel pump? I think someone mentioned possibly bad/clogged fuel injectors? Could the starter be failing? I know part of my thinking is hopium in that the issue might be something topside that would allow me to fix the car while it is immobile and on the ground. It always seems that when you start replacing things on a neglected car (ie previously replaced ignition coil/ECM, sparkplugs, battery, etc), other things decide it's their turn to get attention and fail on you.
It it don't crank there's no reason to worry about anything else.
Last edited by greg8453; Feb 7, 2023 at 02:45 PM.
Thread Starter
Senior Member
Joined: 08-09-2020
Posts: 118
From: tampa bay
i am soooo confused.>>>>> Me too
what does the fuel pump have to do with the starter? >>>>>Wondering if all this starter action is wearing it out causing a new problem - like how the battery died?
When did the car fail to start?>>>>>> Going back to first symptoms - day before car ran/started fine. Next morning it would start and very quickly stall out - did that 2 or 3 times then wouldn't even start, just the starter doing its thing.
How can you have p0171 and p0420 when the motor is not running?>>>>> That was the codes given on the scanner at that time - the 0420 had been there for a year or so off and on.the 0171 showed up about this time or fairly recently as i hadn't checked the codes for a week or so (cel is always on due to the 0420)
the fuel pump only runs for about 20 seconds if the motor does not start.
The fuel pump testing should be done key on motor off. You might need to cycle the key several times to get the pressure high. - >>>>THAT IS HOW I DID THE TEST- this last time i tested fuel pressure it went to 58 and maintained with attempted start but no run/turn over of engine.
P0171 rarely is a fuel pump problem. If there is a current p0420; the test does not run, the computer is in open loop; meaning that the #1 o2 sensor is not being used. The #1 o2 sensor controls the air/fuel mixture. P0171 is about how much correcting the computer is doing, not about how rich/lean the a/f mixture is.
Ignore any code marked "pending" or "historic" or "permanent"; the only ones that matter are "current">>>>>>. Because the car hasn't started since this first occurred, it is giving me no codes at all - also, when i had to get a new battery that wiped the computer memory.
The problem is the p0420 that you have been ignoring, it makes the ecm ignore any input from sensors and forces the computer to guess.
what does the fuel pump have to do with the starter? >>>>>Wondering if all this starter action is wearing it out causing a new problem - like how the battery died?
When did the car fail to start?>>>>>> Going back to first symptoms - day before car ran/started fine. Next morning it would start and very quickly stall out - did that 2 or 3 times then wouldn't even start, just the starter doing its thing.
How can you have p0171 and p0420 when the motor is not running?>>>>> That was the codes given on the scanner at that time - the 0420 had been there for a year or so off and on.the 0171 showed up about this time or fairly recently as i hadn't checked the codes for a week or so (cel is always on due to the 0420)
the fuel pump only runs for about 20 seconds if the motor does not start.
The fuel pump testing should be done key on motor off. You might need to cycle the key several times to get the pressure high. - >>>>THAT IS HOW I DID THE TEST- this last time i tested fuel pressure it went to 58 and maintained with attempted start but no run/turn over of engine.
P0171 rarely is a fuel pump problem. If there is a current p0420; the test does not run, the computer is in open loop; meaning that the #1 o2 sensor is not being used. The #1 o2 sensor controls the air/fuel mixture. P0171 is about how much correcting the computer is doing, not about how rich/lean the a/f mixture is.
Ignore any code marked "pending" or "historic" or "permanent"; the only ones that matter are "current">>>>>>. Because the car hasn't started since this first occurred, it is giving me no codes at all - also, when i had to get a new battery that wiped the computer memory.
The problem is the p0420 that you have been ignoring, it makes the ecm ignore any input from sensors and forces the computer to guess.
