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Code P0172 keeps showing up on my 04 Jeep Grd.Cher.Spec.Edition. The repair book has no answers. Maybe the group here will have better answers. Is there a sensor that need replacement..?? Thanks Ray.

Per previous sujestions, I have replaced the E3 spark plugs with the recomened originals..Have also replaced some sensors, like TPS, Oxygen sensors and others.. Had the PCM reprogramed as recomended a while back..

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Is the code for bank 1 to rich fuel air mix
The above link can help to fix the problem

Posted on Dec 09, 2016

  • Ray Ramos
    Ray Ramos Dec 10, 2016

    Sorry its a 4.0L,,, Thanks for your answer, it helps a lot...


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4.0L or 4.7L engine???????????????????????????
ILL NOT POST THE 50 causes, and guessing endlessly.
i guess getting car serviced is (off the table?) why?
the service manual does not teach diagnosis.!
only lame how to find open wires, endless...
its for service people that are ASE trained on this.
if you read books , real books , on this you will discover that there is a method for this. DIAGNOSIS
No engine stated, are we to guess engines here?
the sensor is for rich,
WJ jeep ,is the real name if in USA, are you?
yes many books show a list of parts that can be bad, causing a wrong reading from a new 02 sensor (100% ok)
what are they?
do you know what closed loop means (o2) and trim?
if not, it be real hard to learn diagnosis,
P0172 is a USA federal coded, invented by us, in 1996 by fed law.
it is universal in meaning, this one code P0 means fed codes.
P1 means factory only codes. p2, p3 same.
lean /rich
if you under stand closed loop servo systems, the FSM
seemingly confusing word become clear
the PCM goes rich, with O2 reading say 0v, lean.
that is how closed loop works on all EFI cars with 02
what that one fact you can see, that exhaust leaks,
they suck air between puTTS, and is 20 % oxygen same as you breath every day at sealevel
this 20 % oxygen hits the 02 tip and it SLAMS to 0v
0v is gross lean
the ECU then sees that goes rich and sets 172s.
there are other causes, "diagnosis"
what are they,
well do you have P03xx errors? misfire.
if one cylinder misfires each miss, sends what, a slug of oxygent to the 02,. and the 02 will see that, and the ECU goes richer.
the ECM can in fact make it worse.
so good spark is #1 here, as is full engine compression
not 50 psi,
1 leaking injector can cause gross misfire.
and air slugs. and 02 going nuts.
there are lots of tests. Ill not post all test, here.
but there many to find the cause,
but Id be all over exhaust leaks.
got 2 or 4 oxygen sensors
not telling me this makes answers wrong or obtuse.

are you using a real scan tool, $150 or a cheap useless $20 code reader?
the real scan tool does live data
what is long term fuel trim, if V6 both banks.
what is any other DTCs , pending
the 172 code has a Freeze frame this set of facts shows
other key readings during said failure, is see you didnt look here first. as you must.
and the live data on all sensors, at idle.
are the IN BAND (means reading correctly) (take a class on EFI?)(
if in band , I bet the 02 bank what ever, bank, front sensor reads
0v all day or reads wrong.
our scan tool I can plot o2 live data in a graph (voltage over time)
it must swing in the correct way. (im not teaching you that)
i have a real scope so i can see them all even on a 1993.
other than a simple exhaust leak
it can be misfire.
even in pendings. (push pendings on scan tool)
IF true there are 50 causes of misfire.
Ill list a few....
bad engine, say and intake valve on the bad bank
bad spark , or marginal, or gapped wrong.
injectors bad, sticking clogged or leaking. (simple tests with gauge)
vacuum bouncing, a simple test. and if true makes all EFI goes nuts...
fuel pressure wrong , out of spec. the FPR can fail here.
my guess you did not read chapter 25?
in the REAL BOOK

Posted on Dec 10, 2016

  • 2 more comments 
  • _-__-___-_
    _-__-___-_ Dec 10, 2016

    why post no engine stated, do you work not knowing this basic fact?
    the above is my best attempt at NOT GUE$$ING
    modern cars are complex, and have complex systems, guessing really does not work.
    take a 2 year ASE school and learn it.
    unless super lucky. (the luck if the Irish?)
    I give you a 1 in 50 chance.
    blind guessing.?
    have you driven it at least 50 miles
    then scan it for the other errors. DTCs's
    or pending DTC./ we need them all.....

    how many miles on car. and engine.???
    when was last full tuneup.
    did you gap the plugs as the service manual tells, not damaging them.
    E3 are not factory authroized plugs
    why use this BS plug."AS seen ON TV"
    here ill quote jeep for you.
    ZFR5N (NGK #) I-6 (inline 6)
    RC12MCC4 , NON HO V8
    NOT MAGIC 'Tv; Plugs
    the books also shows you how not to damage
    the most expensive HO sparkplugs
    read that yet?/ its all in the book by jeep.

    use NGK plugs, and only OEM spec type.
    I persnally do not like CHumpions.

    the I-6 4L has coil rail , is that you?

  • _-__-___-_
    _-__-___-_ Dec 10, 2016

    ok read all your long posts.
    seems it's for fords too
    so I can not figure out what you drive.
    with ford F150 mixed in....
    i do see 1 post of the many with 4.0L I6 engine. this it?
    I see you posted DTC 206 one time.
    injector 6 controls, means the coil in the injector reads wrong. (its and electromag, injector, with internal coil )
    is this fixed?
    or was that the F150 ford.?

  • _-__-___-_
    _-__-___-_ Dec 10, 2016

    if and I6, 4.0l is car california car
    with that splint bank exhaust and 3 oxygen sensors.
    B1S1 (this is cal split systems)
    and B1s2 (rear cat )

    the fed car, (not cal)
    has only ON B1 sensor front. BANK 1.
    no split.
    this too matters. if I6.

  • Anonymous Dec 11, 2016

    no miles on your engine? 50k 500k ?
    no miles since a full tuneup?
    no scan tool data, running.(live data stream)
    just 1 dtc,
    this one 1 DTC will not tell you much.
    in fact tells you what a 1985 jeep tells you
    you smell the unburned fuel, and go, shes rich.
    172 same deal. just the ecu told you and the CAT eat up all that stink.
    why not take the car to any ASE shop
    google ASE shop by zip./



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