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#1763079 - 01/31/10 01:46 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: Mustang_Cougar]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
This is most likely a bad cat or downstream sensor problem.
Because it's the second sensor that tells the computer the cat is bad.
But if you get a new cat, I'd get both sensors, for a bunch or reasons.
It's probably a coincidence about the recent fill up. You have a lot of miles on those parts, and they are normally due for replacement to work their best now.

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#1763086 - 01/31/10 01:50 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
Trav Offline


Registered: 11/20/06
Posts: 9153
Loc: MA, Mittelfranken.de
Originally Posted By: brianl703
[quote=Trav]
A lazy downstream O2 sensor (not bad enough to throw a O2 code)


Explain that one. The ECU caculates a switch ratio by dividing the number of downstream switches by the number of upstream switches. If it exceeds a certain value (.8 on my Crown Vic), a P0420 or P0430 code is set.

A lazy downstream (post cat) sensor would, in fact, reduce the switch ratio, making it less likely that a P0420 or P0430 code is set.

Quote:
..and then the cat (they're goint to want to replace the downstream sensor anyway when they install the new cat)

I wouldn't spend the money to replace the downstream sensor. There's no point to it. It's obviously working well enough if it can switch fast enough to generate a P0420 or P0430 code.



Read for yourself.There are many references to the PO420 code and Downstream O2 sensor issues to be found in any emission book.
http://www.aa1car.com/library/o2sensor.htm
http://www.aa1car.com/library/p0420_dtc.htm



Edited by Trav (01/31/10 01:56 PM)
_________________________
ASE L1, Master. Deutsch Meisterbrief.

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#1763137 - 01/31/10 02:34 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: Trav]
brianl703 Offline


Registered: 05/07/04
Posts: 10487
Loc: Manassas, VA
Originally Posted By: Trav


Read for yourself.There are many references to the PO420 code and Downstream O2 sensor issues to be found in any emission book.
http://www.aa1car.com/library/o2sensor.htm
http://www.aa1car.com/library/p0420_dtc.htm


I've read lots about this, including the Ford TSB where it's stated that replacing the downstream sensor WILL NOT correct a P0420/P0430 issue.

Nothing you linked to suggests that a faulty downstream sensor will cause a P0420/P0430, only that a faulty O2 sensor will affect the accuracy of the catalyst monitor test. Which is true, but (in the case of a faulty downstream sensor) in favor of passing a degraded catalyst, not the other way around...and that's assuming the faulty downstream sensor doesn't get detected as such and a code set for that.

In order for a faulty downstream O2 sensor to cause a P0420 or P0430 code, it would have to fail in a way that causes it to switch faster. That's not how O2 sensors fail.

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#1763162 - 01/31/10 03:02 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
Trav Offline


Registered: 11/20/06
Posts: 9153
Loc: MA, Mittelfranken.de
Quote:
If the downstream O2 sensor is bad (heater circuit not working, loose or corroded wiring connector, contaminated sensor element, etc.), the OBD II system should detect the fault and set an oxygen sensor code. The same goes for a bad upstream O2 sensor. In either case, the presence of an O2 sensor code should prevent the catalyst monitor from running and setting a false P0420 code. Of course, this is ideally speaking and nothing is ever ideal. Sometimes a faulty O2 sensor is not bad enough to set an O2 sensor code but is off just enough to affect the accuracy of the catalyst monitor.



We had a Toyota Camry in a while ago with a new OEM cat and upstream O2 installed and still throwing PO420.
After replacing the downstream the code is gone for over a year now.
_________________________
ASE L1, Master. Deutsch Meisterbrief.

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#1763188 - 01/31/10 03:31 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: Trav]
brianl703 Offline


Registered: 05/07/04
Posts: 10487
Loc: Manassas, VA
Did you look at the Mode $6 data before and after you replaced the downstream sensor? Look at the downstream switch rate with a scantool?


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#1763198 - 01/31/10 03:44 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
brianl703 Offline


Registered: 05/07/04
Posts: 10487
Loc: Manassas, VA
Here, from Ford TSB 01-9-7, are the possible causes of P0420/P0430.

Quote:
Malfunctioning ECT/CHT
•High fuel pressure
•Damaged exhaust manifold
•Cylinder misfiring
•HO2S wiring concerns (shorted or chafed,
bent pins, etc.)
•Damaged exhaust system pipe
•Damaged muffler/tailpipe assembly
•Retarded spark timing
Damaged Catalytic Converter:
•Use of leaded fuel
•Oil contamination/consumption
•Silicone contamination (sealants/cleaners)


Also from the same TSB:
Quote:

Do not replace downstream HO2S sensors for DTCs P0420 and/or
P0430: When diagnosing a vehicle with a
customer concern of MIL On and DTCs
P0420/P0430 in continuous memory, do not
replace the downstream HO2S sensors
(HO2S12/HO2S22). Damaged or malfunctioning
downstream HO2S sensors will not cause these
DTCs to be set. Always verify the vehicle
concern, then perform the pinpoint diagnostics
in the appropriate PC/ED Service Manual.

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#1763359 - 01/31/10 06:28 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
Trav Offline


Registered: 11/20/06
Posts: 9153
Loc: MA, Mittelfranken.de
I have seen that from Ford in the past.
This Toyota had an almost flat wave form on the post O2 every time we checked it when there was no CEL.She would come back with an illuminated CEL and the post O2 was switching erratically for a brief time then stabilizing to an almost neutral line.No O2 codes only PO420 that remained.
This Code would not reappear for a day,a week or sometimes a month prior to changing the post O2.
If i remember correctly this thing almost always came after a highway drive.



Edited by Trav (01/31/10 06:29 PM)
_________________________
ASE L1, Master. Deutsch Meisterbrief.

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#1763390 - 01/31/10 07:11 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: Trav]
brianl703 Offline


Registered: 05/07/04
Posts: 10487
Loc: Manassas, VA
Ford may do things a bit differently than Toyota. Ford's documentation says the computer collects up to several hundred O2 switches over a 900-second period before it makes the determination that the catalyst is good or bad:

Quote:
DTCs P0420 Bank 1 (or Y-pipe), P0430 Bank 2
Monitor execution: once per driving cycle
Monitor Sequence: HO2S response test complete and no DTCs (P0133/P0153) prior to
calculating switch ratio, no SAIR pump stuck on DTCs (P0412/P1414), no
evap leak check DTCs (P0442)
Sensors OK: ECT, IAT, TP, VSS, CKP

Monitoring Duration: Approximately 900 seconds during appropriate FTP conditions (approximately 200 to 600 oxygen sensor switches are collected)


This long test duration probably reduces the impact of a temporary downstream O2 sensor malfunction on the test.


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#1763394 - 01/31/10 07:18 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
brianl703 Offline


Registered: 05/07/04
Posts: 10487
Loc: Manassas, VA
This was the test method used in some early OBD-II Ford vehicles. The impression I get is that the steady-state method does not comply with new regulations so it is no longer used beyond the 1996 model year. A 20-second test is highly susceptible to false positives caused by temporary problems.


Quote:
Steady State Method
The steady-state catalyst monitor performs a 20 second test during steady state rpm and load conditions at higher
vehicle speeds. The monitor is an active/intrusive monitor. During the test, closed loop fuel control is temporarily
transferred from the pre-catalyst, fuel control oxygen sensors to post-catalyst oxygen sensors under specific,
steady state conditions. If the catalyst has sufficient oxygen storage, the closed loop cycling frequency will be much
longer than the cycling frequency observed during normal fuel control. As oxygen storage degrades, the closed
loop frequency from the post-catalyst sensors become short. At the end of the 20-second test period, the PCM
calculates a closed loop switching frequency based on the rpm/load conditions at the time of the test. If the
measured frequency is higher than the catalyst efficiency malfunction threshold frequency, a malfunction is
indicated. Threshold frequencies (Hz) are stored in a calibration table as a function of rpm/load.

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#1763454 - 01/31/10 08:10 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
The rhetoric in the jeep/Mopar FSM basically states that the closer the "like states" between the up:downstream O2 sensor ..the lower the efficiency ..

There will be like states even in a 100% NEW system. There is only so much capacity for O2 uptake by the catalyst during LEAN conditions. There is also only so much stored O2 to release during RICH. If the upstream O2 is slow to react, even with a good catalyst, the downstream will read these efficiency loss indicators.

I'm unsure how the PCM records all data based on the current fuel strategy. For example, let's say your coasting down a very long hill. If you're out of fuel enrichment, the injectors may turn off all together ..NO FUEL to RICH:LEAN. I don't know if the firmware is ignoring these like states only separated by a time delay.
_________________________
http://lube-direct.com/gallan/

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#1763506 - 01/31/10 09:05 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: Gary Allan]
brianl703 Offline


Registered: 05/07/04
Posts: 10487
Loc: Manassas, VA
Ford has certain conditions that have to be met. Since the load must be at least 10%, it probably would not run this test when it's coasting.

Entry condition Minimum Maximum
Time since engine start-up (70 oF start) 330 seconds
Engine Coolant Temp 170 oF 230 oF
Intake Air Temp 20 oF 180 oF
Engine Load 10%
Throttle Position Part Throttle Part Throttle
Time since entering closed loop fuel 30 sec
Vehicle Speed 5 mph 70 mph
Inferred Catalyst Mid-bed Temperature 900 oF
Steady Air Mass Flow for each Air Mass cell (typically five cells) 1.0 lb/min 5.0 lb/min
(Note: FTP cycle is biased towards the low air mass range, 25 - 35 mph steady state driving must be
performed to complete the monitor)
TYPICAL MALFUNCTION

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#1763553 - 01/31/10 10:00 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
strongt Offline


Registered: 03/01/07
Posts: 341
Loc: So. Utah
Yes. I believe that poor quailty or cheap high % ethanol gas will and can cause the P0420 code to pop up in a Chrysler vehicle that has some miles on the 02 sensors.

I've ran into the same code in my 03 Jeep GG with the 4.0L. The code will always pop up if I use any gas that I know has 10% ethanol content in it. I have a scanner that reads real-time sensor info, and when I have a tank of the cheap gas, the upstream sensor reads closer to the downstream reading. Thats when it trips the code.

But when I run a name brand gas through that has a lower ethanol content, the upstream sensor read normal. With a higher number then the downstream sensor. Which means the the Cat is still doing it's job.

I've run this test a buch of times this past year and the results always come out the same:

That cheap, 10% ethanol gas(the gas thats offered in my area at the none brand name stations) effects the upstream 02 sensor. Thus triggering the code.

After a few tanks of brand name gas, the Jeep can pass the emissions testing.

I'd say run the cheap gas thru, then fill up with a good quailty gas and reset the pcm.


Edited by strongt (01/31/10 10:02 PM)
_________________________
2003 Jeep GC 4.0L 187,000 Miles
Chevron 10W30
51085 Wix Oil Filter

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#1763925 - 02/01/10 09:06 AM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
Trav Offline


Registered: 11/20/06
Posts: 9153
Loc: MA, Mittelfranken.de
Originally Posted By: brianl703
This was the test method used in some early OBD-II Ford vehicles. The impression I get is that the steady-state method does not comply with new regulations so it is no longer used beyond the 1996 model year. A 20-second test is highly susceptible to false positives caused by temporary problems.


Quote:
Steady State Method
The steady-state catalyst monitor performs a 20 second test during steady state rpm and load conditions at higher
vehicle speeds. The monitor is an active/intrusive monitor. During the test, closed loop fuel control is temporarily
transferred from the pre-catalyst, fuel control oxygen sensors to post-catalyst oxygen sensors under specific,
steady state conditions. If the catalyst has sufficient oxygen storage, the closed loop cycling frequency will be much
longer than the cycling frequency observed during normal fuel control. As oxygen storage degrades, the closed
loop frequency from the post-catalyst sensors become short. At the end of the 20-second test period, the PCM
calculates a closed loop switching frequency based on the rpm/load conditions at the time of the test. If the
measured frequency is higher than the catalyst efficiency malfunction threshold frequency, a malfunction is
indicated. Threshold frequencies (Hz) are stored in a calibration table as a function of rpm/load.


I can see where this would be a problem.I have no idea what protocols Toyota uses when checking the O2 sensors.
Although the OBD II protocol is specific about which functions are tested,monitored and generic codes generated there does seem to be differences between manufacturers about how the testing is performed.
Toyota seems to have more than an average amount issues with PO420/430 and some Ford models have issues running the EVAP monitor.While they do run the same test they perform it differently.

As to the bad gas question one of my guys remembers a GMC Denali he did that tossed a PO420/430 within a few miles after putting a bottle of Redline Sl1 in the tank.
So it would seem that its possible,after resetting the CEL it didn't come back.
_________________________
ASE L1, Master. Deutsch Meisterbrief.

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#1763976 - 02/01/10 09:45 AM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
The downstream sensor can fail in more than one way.
It for sure can cause a 'bad cat' code.
It's not necessarily a fact in this case, but it sure can.

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#1805318 - 03/05/10 06:55 PM Re: Can poor quality gas cause a P0420 (Cat Failure)? [Re: brianl703]
pennzoil_guru Offline


Registered: 11/05/04
Posts: 164
Loc: Northern York Region, Ontario,...
I had the same code. The freeze frame data looked normal except the coolant temp read 194 F. I know this is wrong because it was about 2 C (36 F ) outside and the car had only been running for about 7 to 10 minutes after sitting for 12 hours when the CEL came on. Could a faulty ECT sensor reading warmer coolant than actual trip this code ( ie, the ECM would incorrectly lean out the AF ratio)?
_________________________
2011Toyota Matriix TGMO 0W20
2006 Toyota Sienna Valvoline Premium Conventional 5W20 (free jug)


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