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Car problem..O2 sensor and bad mileage

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,437
1,017
My own world inside my head
No No No, your not doing a voltage drop because of heat build up... Your doing it because an Ohms meter uses an extremly minimal amount of power...... Lets say you have a connection your tyring to test... you check the resistance, and you get .12 ohms.... In the auto world, thats a good connection.... BUT... lets say that connection has 30 strands, and 29 have severed.... the amount of power the Ohms meter uses will still give you a solid read for ohms.... But as soon as you load the circuit, it cant carry the power. So you check voltage from each side of it...... What your actually reading is a backfeed of power<you dont want any> So the higher the voltage, the worse the connection..... Remember Ohms you have to isolate, then read... on alot of these automotive connections its nearly impossible to actually isolate what your testing.... Other problem, alot of sensors/solenoids will ground out in default off.... This is were you can run in to major problems trying to test ground connections.... Youll backfeed your resistance reading into another circuit, even if the circuit is bad, it can read good.....A Voltage drop test reads what a connection is doing on a live circuit.... So you have to remember to power up the circuit your testing.........Works wonders.


Not trying to say Ohms readings arent usefull, but when looking for reall application reisstnace, you want the voltage drop
 

Westy

the teste
Nov 22, 2002
54,235
20,018
Sleazattle
No No No, your not doing a voltage drop because of heat build up... Your doing it because an Ohms meter uses an extremly minimal amount of power...... Lets say you have a connection your tyring to test... you check the resistance, and you get .12 ohms.... In the auto world, thats a good connection.... BUT... lets say that connection has 30 strands, and 29 have severed.... the amount of power the Ohms meter uses will still give you a solid read for ohms.... But as soon as you load the circuit, it cant carry the power. So you check voltage from each side of it...... What your actually reading is a backfeed of power<you dont want any> So the higher the voltage, the worse the connection..... Remember Ohms you have to isolate, then read... on alot of these automotive connections its nearly impossible to actually isolate what your testing.... Other problem, alot of sensors/solenoids will ground out in default off.... This is were you can run in to major problems trying to test ground connections.... Youll backfeed your resistance reading into another circuit, even if the circuit is bad, it can read good.....A Voltage drop test reads what a connection is doing on a live circuit.... So you have to remember to power up the circuit your testing.........Works wonders.


Not trying to say Ohms readings arent usefull, but when looking for reall application reisstnace, you want the voltage drop
Sorry. V=IR. The resistance will functionally be the same between the working load and the load used by a resistance meter. If a wire is near broken the one strand will increase the resistance but it will under all realistic load conditions. Typically the effective length of the wire with only one working strand is so short it has very little impact on the resistance whether it is pulling .0001 amps or 2.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,437
1,017
My own world inside my head
To help explain how toa bit more on a voltage drop... I dropped some mad skills in the paint program



Ok Diagram shows a battery, chassis style ground, a switch, a motor, multiple junctions<shown as a box with a letter near it>and points at which to test

To test Junction A, youl put Postivie lead on test point 1, Neg on test point 2.. if its good, youll read zero or near zero on a volts scale, if its broken completly, youll read battery voltalge

To test the switch, itll be test point two, for positive, test point three for negative

Junction B will be Pos on three, Neg on four

Motor, Pos on four, neg on five....<remember circuit needs to be running for a voltage drop.... If the motor is good, and running, Youll read zero or near zero... If it has an open condition, youll read battery voltage

Junction C..Pos on five, neg on six

Junction D Pos on six, neg on seven



That should give you the general idea of a voltage drop test..........., andd why its so accurate
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,437
1,017
My own world inside my head
Ok, just went through mitchel. Your system WILLNOT RELEARN THE O2 WHEN RESETTING WITHA GENERIC SCANNER.

When you reset without the generic scanner, there is a Much different procedure to the process.

First step is to loosen and retighten all ground locations, this makes sure the vehicle is getting good grounds. Next step is to clear the codes with the scanner you have.

Start the vehicle and bring it to operating tempurature, make sure there are no codes at this time. This is the strange part when nt using the Nissan tool......it will not relearn new values untill you do this step.

Stop the engine, unplug the Mass air flow sensor... start the engine and allow it to idle for about 30 seconds. Ensure that the code for MAF ciruit comes on..... plug the sensor back in witht he engine running....... Clear codes again...WITH ENGINE RUNNING...... shut it off, restart, and let idel for at least ten minutes then go for a drive.





Hope that helps out, it was pretty clear that this code isnt being set for a poor O2, but a ground problem.
 

SkaredShtles

Michael Bolton
Sep 21, 2003
65,379
12,533
In a van.... down by the river
Ok, just went through mitchel. Your system WILLNOT RELEARN THE O2 WHEN RESETTING WITHA GENERIC SCANNER.

When you reset without the generic scanner, there is a Much different procedure to the process.

First step is to loosen and retighten all ground locations, this makes sure the vehicle is getting good grounds. Next step is to clear the codes with the scanner you have.

Start the vehicle and bring it to operating tempurature, make sure there are no codes at this time. This is the strange part when nt using the Nissan tool......it will not relearn new values untill you do this step.

Stop the engine, unplug the Mass air flow sensor... start the engine and allow it to idle for about 30 seconds. Ensure that the code for MAF ciruit comes on..... plug the sensor back in witht he engine running....... Clear codes again...WITH ENGINE RUNNING...... shut it off, restart, and let idel for at least ten minutes then go for a drive.





Hope that helps out, it was pretty clear that this code isnt being set for a poor O2, but a ground problem.
After all that... I'm betting this would work better for loco:

 

ultraNoob

Yoshinoya Destroyer
Jan 20, 2007
4,504
1
Hills of Paradise
My $0.02 after reading the thread.

Situation:
- SES on, DTC P1163 Fuel Trim Inactive Per Ignition Bank 1 High
- marked drop in fuel mileage
- Oxygen Sensors B1S1 & B2S1 replaced (both sensors before primary cats right and left side respectively)

Assumptions:
- all ground points checked, cleaned and verified
- battery voltage is between 12.6V-13.4V
- aux ground attached from neg battery termial to intake manifold (for good measure)
- 12v power and ground for O2 Sensor heater exist
- continuity from O2 sensor signal wire to ecu harness exists

Analysis:

First off, if there were any intake vacuum leaks or exhaust leaks localized to a specific cylinder, other DTC would be present (e.g. P0302 misfire cyl 2, cyl 3, etc...)

Secondly, Dirty is right when he says that there are more than just O2 sensors that dictate your fuel mileage. I can't even begin to count how many times I've worked on vehicles where the existing codes are P0171 System too lean bank 1 and P0174 System too lean bank 2, and the customer or other shops immediately replace the O2 sensors.

Your situation where the service engine soon "SES" light (aka check engine light) is illuminated, only one DTC exists, and there is a drop in fuel mileage could point to problems other than your O2 sensors.

Let's first look at your freeze frame data. Freeze frame data is a recorded list of component outputs and measured data at the time the DTC was set. For your situation, I'd be interested in the following pieces of data:
- engine speed (RPM)
- engine load (%)
- vehicle speed (mph)
- ambient temp (degF)
- MAF reading (V or g/ms)
- Long Term Fuel Trim Bank 1 (LTFT 1 %)
- Long Term Fuel Trim Bank 2 (LTFT 2 %)

Properly working oxygen sensors have one major function; send a signal to the ecu. That signal can range from 0.05v to 0.95v. Although most sensors nominally send out a signal between 0.1v and 0.9v. It is up to the ECU to regulate the A/F ratio which in turn causes the O2 sensor signal to rise or fall within the specified range. The ECU collects this data and creates an average. This average is then compared to the "ideal" average and a long term fuel trim is calculated.

A perfect fuel trim is 0% + 5%. 0% fuel trim means that the engine is consuming an air (oxygen) to fuel ratio of 14.7:1. When the amount of incoming oxygen varies due to altitude, ambient temp, or load the ECU reads the O2 sensors, and along with other data from sensors such as the throttle position sensor, engine coolant temp sensor, etc.. and moves to adjust the air fuel ratio to once again achieve a 14.7:1 ratio. A positve long term fuel trim percentage means that the ecu is opening the fuel injectors x% longer than normal, while a negative LTFT means that the ecu is opening the fuel injectors x% shorter than normal.

Code 1163 is a fuel trim malfunction, meaning that the ecu is unable to properly regulate the air fuel ratio. Common causes can be:
- insufficient battery voltage
- insufficient ground to ecu
- insufficient ground to sensor (02, tps, ect, maf)
- insufficient power to sensor (02, tps, ect, maf)
- sensor failure
- ecu failure
- contaminated or ill fitting harness connections
- insufficient/excessive fuel pressure
- insufficient ignition voltage
- intake vacuum leaks
- localized exhaust leaks
- failed wiring insulation (common on most hight mileage nissan vehicles)
- there are other possible causes, but from my experience, these are the most common

If the DTC is still present, write down all the freeze frame data and let us know. More information is needed to provide an educated guess. Good luck.
 

loco-gringo

Crusading Clamp Monkey
Sep 27, 2006
8,887
14
Deep in the heart of TEXAS
Thank you all for all of your input. Very good advice. The mechanic has been super willing to listen to tidbits, but I've worked on some stuff myself. I confess to not knowing how to check for ground faults, but I tried. I did reset the ECM with the steps Dirty told me to do and I have driven about 35 highway miles and the O2 sensor has not tripped again. Perhaps the codes hadn't been cleared right at the shop. I doubt I'm that lucky, but we'll see. I'll drive it a few days and check the mileage. Perhaps this is all it takes. Heaven knows I could use some good luck on this thing right now.

Thanks again for the help.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,437
1,017
My own world inside my head
Sherm has a nice list there, thats all teh stuff I am always looking at with about every runability job I have.....

Sherm, You are SOooo right about teh 171 and 174.... Sooo many times I have a custoemr that went to autozone for a free checl, then they go home with three bills of O2 sensors... only to come to me to see it didnt work......I find that those tow are almost never the o2's, but a vacuum leak.... if its a ford< I know Im pigeon holing a bit> first thing I look at is the PCV line, specially seeing how much those little bastiges fail.... Nine times of ten, Ill find it with a big hole in it.

I think the big thing for loco's that stands out for me is the drop in milage. With what I got from Mitchell today, and a couple tsb's for his model, figured a proper PCM reset was in order.

Curious form here to see how it goes. If its still an issue I do think its going to be the milage that is the true indicator as to whats happening... Any more thoughts on it?

For me If it were at the shop, I would of course start with all the simple basic checks....But I would check FP, check for vacuum leaks, do an inj leakdown test, probably get an alternator wave for good measure.
 

ultraNoob

Yoshinoya Destroyer
Jan 20, 2007
4,504
1
Hills of Paradise
Sherm, You are SOooo right about teh 171 and 174.... Sooo many times I have a custoemr that went to autozone for a free checl, then they go home with three bills of O2 sensors... only to come to me to see it didnt work......I find that those tow are almost never the o2's, but a vacuum leak.... if its a ford< I know Im pigeon holing a bit> first thing I look at is the PCV line, specially seeing how much those little bastiges fail.... Nine times of ten, Ill find it with a big hole in it.

Most common thing I'm seeing especially on fords is the evap hose directly off of the intake manifold. After about 100k, those things just disintegrate.
 

ultraNoob

Yoshinoya Destroyer
Jan 20, 2007
4,504
1
Hills of Paradise
Oh yea. Forgot to mention that I drive a 2000 Xterra with 272k. Ran into a bad fuel mileage problem last year. Turned out to be an over active fan clutch. Swapped it and BAM! Back to normal.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,437
1,017
My own world inside my head
Oh yea. Forgot to mention that I drive a 2000 Xterra with 272k. Ran into a bad fuel mileage problem last year. Turned out to be an over active fan clutch. Swapped it and BAM! Back to normal.
Dude speaking of locked up fan clutches.... Why does it always seem things like this come in waves..... Ive done at least half a dozen in the last week... Couple fords, couple chevy's, couple imports..... strange I say...Strange....... Oh yeah, gotta love how ford and chevy decided to take away the thermal bi metal spring, and add an electronic engagement system...........Love it on the fords, hate it on the chevy's....
 

RICHARD

Chimp
Feb 17, 2010
1
0
i think you should drive your car in between 40 to 50 km per hour which will make your engine smooth and also it will produce less smoke
and if you are not satisfied with then you should just check www.iSuck wchich will be more helpful for you and you will more help!!!!
 

jdcamb

Tool Time!
Feb 17, 2002
19,799
8,383
Nowhere Man!
i think you should drive your car in between 40 to 50 km per hour which will make your engine smooth and also it will produce less smoke
and if you are not satisfied with then you should just check www.iSuck wchich will be more helpful for you and you will more help!!!!
Boy I thought SS was smart but this guy knows his chit!.....
 

loco-gringo

Crusading Clamp Monkey
Sep 27, 2006
8,887
14
Deep in the heart of TEXAS
i think you should drive your car in between 40 to 50 km per hour which will make your engine smooth and also it will produce less smoke
and if you are not satisfied with then you should just check www.iSuck wchich will be more helpful for you and you will more help!!!!
Do you think I'm Canadian??? I'm in Texas. We use miles here. The car doesn't smoke. I don't hate freedom. Besides...wouldn't this yield better kilometerage, not mileage???
 

loco-gringo

Crusading Clamp Monkey
Sep 27, 2006
8,887
14
Deep in the heart of TEXAS
Turns out the first shop might have replaced the wrong O2 sensor. They replaced bank 1 sensor 2 this time and I think they were replacing bank 2 sensor 1 before. We'll see. $360 this time, so I'm hopeful I'm done spending.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,437
1,017
My own world inside my head
Turns out the first shop might have replaced the wrong O2 sensor. They replaced bank 1 sensor 2 this time and I think they were replacing bank 2 sensor 1 before. We'll see. $360 this time, so I'm hopeful I'm done spending.
Ummmm.... make sure you take the bill back to the first shop, and get your money back.... Anyone that does any type of Diag should know that a downstream<sensor two> does nothing for fuel trim, or the ability to control it, the downstream o2's only job is to moniter tha catalytic converter.
 

loco-gringo

Crusading Clamp Monkey
Sep 27, 2006
8,887
14
Deep in the heart of TEXAS
Ummmm.... make sure you take the bill back to the first shop, and get your money back.... Anyone that does any type of Diag should know that a downstream<sensor two> does nothing for fuel trim, or the ability to control it, the downstream o2's only job is to moniter tha catalytic converter.
I hate to be the one to say I'll just suck it up, but the first shop has done enough favors that for $200, I'm not going to buck the system. I trust few people, and while a mistake appears to have been made, I trust them. That's worth $200 to me.