Question about 2006 Suzuki Forenza

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Engine light on code reads bad cat replaced it light returns reads ox senors replaced it light returns reads cat gone bad.

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Just remove the batt for 15 mins and check

Posted on Nov 08, 2013

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  • Suzuki Master
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The ECU (brain) has no idea at ALL what is broken!
it only knows 2 things, bad inputs. and failed tests.
nothing else. The brain is not AI (artificial intelligence)
Not even and expert system , yet.
that is the job of and ASE mechanic
to find the cause. and not GUE$$.

your failure to state the DTCs reported , sorry, is bad news to anyhelper, sorry!
420s. is , weak CAT test. but in most case it's not the CAT.
senors replaced? 1 or both.? B1S1 and B1S2?

Did you get o2 (oxy) DTC failures?, if yes, ignore all cat fails.!
if other codes/ DTC, that too, means ignore cat failure.
the CAT monitor (P042x) only is valid if the engine runs prefectly.
if not the CAT overheats or underheats( goes dead cold)\

the cat will over heat, (cel flash madly) for gross engine over fueling (1 example , bad fuel reg, and pressure at 60PSI)
the cat glows red hot , or near. and the test may fail.
case 2: the engine (AFR fuel) is grossly lean the CAT may go under temperature and drop off line.
we call this CAT no lit off, it has a minium working temperature.
as air leaks in front of the cat causes EFI to go very rich.
and leaks behind can make the rear 02 go nuts. and lie
and say, bad Cat.
all this is the domain of the ASE mech. he knows all stuff.
and never ever lets the ECU tell him what to do.;
it does tell him (suggests) a battery of test.
hope that helps,
post all stored, DTC,all pending and the full freeze frame data
and if cagey? the closed loop status hot idle.

Posted on Oct 14, 2013

  • 11 more comments 
  • _-__-___-_
    _-__-___-_ Oct 20, 2013

    btw2, my cat was filled to top with Antifreeze and engine oil, i drove it (new engine) for 50 long miles, and baked it dry, it woke up, and started working 100% , passing the P042x tests. proving there is always hope for the cat. I did this just to prove that fact. I had my EFI running first in closed loop at idle and light cruise. so that fact allowed the cat to bake dry, if EFI is in Limphome mode, none of this works. at all.

  • _-__-___-_
    _-__-___-_ Oct 23, 2013

    first get engine running perfect. the let cat bake dry, and self clean. if not getting smog checks most folks ignore, it, but if you have air leaks, near the 02 sensors that does make the engine run bad. check fuel trim and closed loop status for normal running of the 02 sensors. if they are all 100% good the cat is bad.

  • _-__-___-_
    _-__-___-_ Oct 24, 2013

    the ECU on some cars skip the P042x test, if other DTCs are stored, but the ECU can lul its self in to think all spark and EFI fueling is perfect and then run the P42x monitor. (bad luck) The CAT can be overloaded, (read the spec on cats. ) If the Engine is running real bad, do not look at P042x (its last to worry) if you have full power, no DTCs, no pendings, for misfire. and LTFT long fuel trim is good say -4% ,then it might be just and crack near B1S2 (rear o2sensor) or hell the wires fell off or or melted, or B1S2 migth be just bad. A new cat can cost $1000 installed you can buy a new PNP sensor for $50 and screw it in your self,(just plug it in) Some cats can in fact break up inside, causing huge back pressures, tesing this is easy with front 02 pulled and pressure gauge attached, max 2psi at 2500 rpm. it will be way less. dont let eager mech, throw on a cat , just to find out its not bad, the P042x means that the rear sensor reads wrong, NOTHING else.

  • _-__-___-_
    _-__-___-_ Oct 24, 2013

    gets it right !

  • _-__-___-_
    _-__-___-_ Oct 24, 2013

    h tt ps://w w

  • _-__-___-_
    _-__-___-_ Oct 24, 2013

    remove spaces in http and www , and read the whole page, its the best ive ever seen. He hits every spot.

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    post the DTCs ! i presume you have a scan tool , right and know how to push the reset button, right? and know that the cat tests P042x are useless if the O2 are bad, or you have air leaks. post ALL DTCs, thrown after you reset them then drive 20mile, and see if all Oxy monitors and cat monitor is complete, if not drive more over 50mph. when the monitors complete, and NO DTCS is stored, then you fixed it, and be advised, throwing parts at DTCs is a big waste of cash, you make parts stores rich ! why not diagnose the real cause. why not?

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    the ECU on your car never ever knows what is broken

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    the ecu only can report tests (monitors) that fail, not PARTS!

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    do you have a scan tool? if yes, report actual. DTCs all of them.

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    your scan tool has a reset DTCs (all) button see that?

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    did you know that a simple air leak can cause all this? not $1000 in parts. do you?

  • _-__-___-_
    _-__-___-_ Nov 08, 2013

    what DTC'S? post them all.



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