Recently purchased a 96 FJ80 and it had been sitting for a while. Went to get a smog test and everything passed except the Cat monitor needs to reset due to insufficient mileage (according to my OBD scanner). My mechanic said to drive it for a while. After 250 miles the thing has not reset. Does anyone know the drive cycle for resetting? I have searched and cannot seem to find a valid link. Thanks
Driving cycle to reset Cat monitor for smog
- Thread starter Bigbarlo
- Start date
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NLXTACY
Wits' End
It all depends on the condition of the cat. I JUST went thru this on my CARB testing. It took 320 miles to get it to finally register. It shouldn’t take so long and is a clear indicator it needs to be replaced.
Attached in this thread, post#5.
It's a Lexus document.
OBDII Emissions - Catalyst Monitor Not Ready
It's a Lexus document.
OBDII Emissions - Catalyst Monitor Not Ready
Basically the "recommended" drive cycle is impossible to reproduce if you live in any sort of city. But do try to follow the recommended idle times. Follow the thread above ^^^ and get a torque app to see what your o2 sensors are actually doing.
It fixed my problem, but your situation might be different. I would try to diagnose before you start spending money on parts. Get the torque app (free) and look at the o2 sensor readings, take screenshots, and then ask @Bambusiero , since pretty much everything he said was spot on when I was going through this problem.
- Thread starter
- #7
Will do. Thanks
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Totally agree with @Heckraiser.
Observe the O2 waveforms for yourself 1st, before anything else.
Then scratch your head about what the heck it means.
Then diagnose the operational status of all your components.
Your chance of 1st time success will be very high, compared to groping around in the dark with just the MIL (Malfunction Indicator Light), or even the OBD2 error code.
Much was said in that other thread, no need to repeat. Study that.
But I will repeat this, for emphasis:
Any existing or pending MIL code will halt the readiness drive cycle.
You must be completely free of error conditions to make DTC progress.
Observe the O2 waveforms for yourself 1st, before anything else.
Then scratch your head about what the heck it means.
Then diagnose the operational status of all your components.
Your chance of 1st time success will be very high, compared to groping around in the dark with just the MIL (Malfunction Indicator Light), or even the OBD2 error code.
Much was said in that other thread, no need to repeat. Study that.
But I will repeat this, for emphasis:
Any existing or pending MIL code will halt the readiness drive cycle.
You must be completely free of error conditions to make DTC progress.
- Thread starter
- #9
Assuming the above waveforms represent "normal" steady state mid-throttle cruising, fully warmed up.
O2S1 is banging up and down, full scale - means 3 things.
1) The #1 (upstream) sensor wires are connected. Good.
2) The sensor is working OK, reacting to constantly varying gas stream chemistry. Good.
3) The ECU fuel injector control system is working - lean, rich, lean, rich, etc. Good.
O2S2 is pretty much flat line at the lean end, near zero volts. Not reacting to anything.
> He's dead Jim > replace O2 sensor #2.
After it's replaced, take another look. Compare before, after.
Should see an obvious difference with time spent around mid-scale.
But, whatever you see then will tell you about the catalyst function status.
O2S1 is banging up and down, full scale - means 3 things.
1) The #1 (upstream) sensor wires are connected. Good.
2) The sensor is working OK, reacting to constantly varying gas stream chemistry. Good.
3) The ECU fuel injector control system is working - lean, rich, lean, rich, etc. Good.
O2S2 is pretty much flat line at the lean end, near zero volts. Not reacting to anything.
> He's dead Jim > replace O2 sensor #2.
After it's replaced, take another look. Compare before, after.
Should see an obvious difference with time spent around mid-scale.
But, whatever you see then will tell you about the catalyst function status.
- Thread starter
- #11
Picking up the #2 tomorrow. Thanks again for your help.
I know this is a month old already, but came across it in a search..
@Bambusiero , the advice you gave here is incorrect. The post 02 IS suppose to have a near flat line close to zero volts. This means it is working and the cats are doing their job. By the catalysts converting the gases, there will no longer be a fluctuation in rich/lean cycling. If the rear 02 is showing a wave form like the front sensor, it is an indication of bad catalytic converters.
~Paul
You are correct that it should be showing a flat line, but not at zero. That would indicate a faulty second sensor or wiring. If the cats are working properly, you'll get a flat line somewhere in the middle (0.3 in my case)
Agree partly, but partly not.
My understanding is :
While in closed loop control, the goal of the control system is to achieve perfect stochiometric mixture.
However, there are 2 factors that make it a bit more complex than simply keeping the mixture correct all the time.
1) Our (old fashioned) narrow band O2 sensors give about half scale output when the mixture is stochiometric, but the sensors are very sensitive. They have a very steep gain curve, and only indicate the mixture accurately over a narrow range above and below stochiometric. That's why they call them "narrow band".
A little lean - it pegs at negative full scale = 0.0V or so.
A little rich - it pegs at positive full scale = 0.7V or so.
2) Three way catalytic converters work by temporarily storing chemicals so it can make the opposite chemicals combine, because it's dealing with both unburned hydrocarbons and excessively burned oxides of nitrogen. Tough job. So it needs rich - lean - rich - lean.
So - that's what the control system does on the upstream side (O2 sensor #1)- rich - lean - rich - lean.
But it's still shooting for stochiometric mixture, but only on average.
The catalytic converter does the averaging, and the downstream side (O2 sensor #2) should verify stochiometric, a smoothed waveform - about half scale.
Control system engineers call this sort of thing a "bang-bang" controller.
It's one of the least sophisticated types, but actually works pretty well in the real world.
Old fashioned furnaces and air conditioners work this way. Most car A/Cs do.
So, like @Heckraiser said.
BTW, these systems will tolerate a pretty degraded catalytic converter that gives a downstream waveform that's nowhere near a mid-scale flat line, before it gets pissed and throws a P0420 penalty flag on the field. As long as it spends some time around the middle.
While I appreciate your efforts, I understand how the systems work. My statement was "close to zero" not "zero" It was not your voltage advise I was questioning. I was clearing up the implied advice, that the second 02 should have an active wave form, it should not.
At least that is how I read your statement. Just wanted to make sure it was clear to OP.
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- Thread starter
- #18
I drove it for 400+ miles and did the cycle as best as I could but I had to get new cats . After the new cats it almost immediately was good.
Hmm... @TYM4FUN, I am indeed confused by which thing, in particular, you are correcting.
Above you said:
"The post 02 IS suppose to have a near flat line close to zero volts. This means it is working..."
Voltage seemed to be the main point you were making?
But, if everything were working, this would indicate an average lean condition. Average stochiometric mixture is what it wants to see, which is around sensor mid scale, so very roughly 0.3V to 0.5V, not near zero.
Stuck near zero will probably earn you some kind of error code, or maybe just lack of the cat readyness code.
"By the catalysts converting the gases, there will no longer be a fluctuation in rich/lean cycling. If the rear 02 is showing a wave form like the front sensor, it is an indication of bad catalytic converters."
Agree completely here, except that, as an old age allowance, you can have an old degraded cat, not quite dead yet, with a pretty active downstream waveform. They seem to allow considerable leeway for that.
I brought back an expensive OEM mandrel bent stainless steel tube / dual cat metallic core header system from the dead (P0430) to passing, by doing the hot citric/oxalic acid de-scaling treatment. Downstream waveforms before treatment were identical to upstream, indicating good working downstream sensors, but dead cat. After treatment (P0430 went away) were still banging full scale, but paused about 20% in the mid-scale region, and it was OK with that.
Not sure what implication about waveforms you might be referring to, but, I generically call any waveform a waveform, even flat ones.
Requires more descriptive words to get specific.
Above you said:
"The post 02 IS suppose to have a near flat line close to zero volts. This means it is working..."
Voltage seemed to be the main point you were making?
But, if everything were working, this would indicate an average lean condition. Average stochiometric mixture is what it wants to see, which is around sensor mid scale, so very roughly 0.3V to 0.5V, not near zero.
Stuck near zero will probably earn you some kind of error code, or maybe just lack of the cat readyness code.
"By the catalysts converting the gases, there will no longer be a fluctuation in rich/lean cycling. If the rear 02 is showing a wave form like the front sensor, it is an indication of bad catalytic converters."
Agree completely here, except that, as an old age allowance, you can have an old degraded cat, not quite dead yet, with a pretty active downstream waveform. They seem to allow considerable leeway for that.
I brought back an expensive OEM mandrel bent stainless steel tube / dual cat metallic core header system from the dead (P0430) to passing, by doing the hot citric/oxalic acid de-scaling treatment. Downstream waveforms before treatment were identical to upstream, indicating good working downstream sensors, but dead cat. After treatment (P0430 went away) were still banging full scale, but paused about 20% in the mid-scale region, and it was OK with that.
Not sure what implication about waveforms you might be referring to, but, I generically call any waveform a waveform, even flat ones.
Requires more descriptive words to get specific.
