OBDII Warning Won't Clear (1 Viewer)

[flyingmonkey]

Having an issue getting my truck to pass smog. I've been clearing the P0420 for the last year or so. Took it to smog station and emission readings are great and well within min/max or whatever. However, there is an OBDII warning present (C) so I failed. Decided to replace O2 sensors, drove 80-90 miles and warning is still there.

Anyone have a real (meaning better than my $20 amazon one) diagnostic tool? Need to see what's going on so I can fix it. I figure at this point it's either an exhaust leak or bad cat(s).

 

[BreckenridgeCruiser]

I think you are right on... I found this...

P0420 Diagnostic Code - Trouble Code Diagnosis Guide | Toyota Parts Center

Error Code P0420 - Or Catalyst System Efficiency Below Threshold (Bank 1) - Is One Of Several Trouble Codes That Fall Into The General Exhaust System Code Block.

parts.olathetoyota.com

So I'd check for a leak first as it's probably a lot cheaper, but then check the cat for holes or blockages before you replace. Looks like the p0420 means that you have inconsistent readings for a well functioning cat. or being its a 420 code you need to hit a dispensary...

 

[elripster]

I do. It's a blue tooth obd reader and you can build displays in your phone/tablet with the app. You can then watch values as you drive to see what might be going out of range. OBD diagnostics are set and cleared by the ratio of good / bad samples so you could have a part that's in range at idle but goes in/out under load. An 80 gets the high/low idle test so a scenario like that is very plausible.

This is the tool, it's actually quite cheap.. Amazon product ASIN B011NSX27A

Frank

 

[elripster]

We need to measure your cat temp with the IR thermo and see if it is getting up to temp. It should get over 300C. It's just hanging around 80-150C while revving the engine the cat is likely clogged up and/or bad.

Frank

 

[Loober]

Warning and monitor not being set is two different things. Smog is only dependent on the monitors being set, which means the computer has gone through its cycles. If monitors are set and CEL is not on, you'll pass. Make sure you are looking at the right things. I can tell you some trucks take a while for all the monitors to set, there are specific driving cycles that it must go through. The catalyst is usually the hardest one, my tacoma took 1000miles sometimes.

 

[flyingmonkey]

Warning and monitor not being set is two different things. Smog is only dependent on the monitors being set, which means the computer has gone through its cycles. If monitors are set and CEL is not on, you'll pass. Make sure you are looking at the right things. I can tell you some trucks take a while for all the monitors to set, there are specific driving cycles that it must go through. The catalyst is usually the hardest one, my tacoma took 1000miles sometimes.

Yeah, me not knowing the difference between a monitor and a warning is probably part of the problem. There is no check engine light on, but the OBD shows a falshing C. The smog person said I have to drive it for it to clear, so that sounds like a drive cycle so I think what I am referring to is a monitor being set then. I was using the term warning to refer to monitor. So I guess my (C) monitor is not set. I hope it doesn't take 1000 miles! The DMV late fees are starting to add up already and with the price of gas that's like $362,958.27 total!!

So does Warning=CEL and Monitor=something flashing on OBD but no CEL?

 

[Bud_Dude]

Around 1998 on my 1990 FJ62 I had a persistent problem with excessively rich mixture causing a check engine light, and crappy gas mileage. Escondido Toyota took three runs at trying to fix the problem, first declaring the O2 sensors as bad and replaced them for too much money... The problem persisted, so they declared the injectors faulty and replaced them as well, for way too much money... Again the problem persisted, so they decided it was bad catalytic converters and oh by the way the new O2 sensors had been burned up due to the problem, so they replaced the cats and O2 sensors again, for a s*** load of money... And the problem persisted... After wasting nearly $2K at Escondido Toyota I gave up on them and took the truck to what used to be Mark's Automotive in Escondido (allegedly 'the Land Cruiser shop' in North County at the time), now it's Brian's Automotive now and remains my go to place for things above my ability or interest. Their technician 'Kenny' checked the blinky code (pre OBDII) and called a technician friend at Escondido Toyota who faxed over a copy of the troubleshooting page from his FSM for that code. The very first item on the troubleshooting list was to check the fuel pressure at the fuel bar with a 'banjo' fitting. The pressure was way too high and Kenny concluded it was a bad fuel bar pressure regulator, a $50 part at the time and maybe $100 in labor and the problem was finally fixed. There's a moral to that story in there somewhere... but my faith in the dealership as a viable service shop was forever lost.

 

[Bud_Dude]

Yeah, me not knowing the difference between a monitor and a warning is probably part of the problem. There is no check engine light on, but the OBD shows a falshing C. The smog person said I have to drive it for it to clear, so that sounds like a drive cycle so I think what I am referring to is a monitor being set then. I was using the term warning to refer to monitor. So I guess my (C) monitor is not set. I hope it doesn't take 1000 miles! The DMV late fees are starting to add up already and with the price of gas that's like $362,958.27 total!!

So does Warning=CEL and Monitor=something flashing on OBD but no CEL?

My old 2006 Dodge Grand Caravan that I keep around for use as a truck to haul things has a CEL related to the transmission that prevents it from passing smog. So there's a game I have to play every two years to get it to pass smog and it's all about the drive cycle. Basically, I've got to get the van into the shop just as the OBDII smog readiness checks are all green (following the clearing of the CEL with my generic Bluetooth OBDII monitoring device and associated app on my iPhone...). By digging around on the interweb I found what seemed like the best Drive Cycle for the van and it worked pretty well and most importantly, predictably. So I could map out a drive sequence and show up at the smog shop just as all the stars were aligned. Prior to that it was much more of a guessing game and many times I'd be on final approach to the shop as the damn CEL would come back on and have to start over again.... I had a similar CEL issue on my '95 80 series, but luckily the smog shop didn't care about the CEL on that model year, only on 96 and newer...

Long story short, I found this drive cycle on the web... who knows if it's accurate for the FZJ80 or not though, it'll probably take some experimentation:
Here is a drive cycle that works well on Toyotas when trying to set the readiness monitors to pass an emissions test. I developed this myself by trial and error.

• Fuel tank at 1/2 full.
• Engine cold start idle for 10 minutes.
• Drive at highway speed 55-60 mph with steady throttle for 16 minutes.
• Return to idle for three minutes with engine running in park.
• Drive again at medium speed 40 mph for eight minutes.
• Return to idle for three minutes.
• Repeat next day.

You can read the whole article here... Toyota Drive Cycle for Setting Smog Check Readiness Monitors - https://axleaddict.com/auto-repair/Toyota-Drive-Cycle-Readiness-Monitors-for-Emissions

 

[elripster]

So did the smog shop fail you because of the warning even though you have no CEL?

From the description it sounds like the pre and post cat O2 sensors aren't reading sufficiently differently enough. If the truck passed smog with flying colors and the cats are heating up, I think taking a good look at the wiring would be next. I think if you can get a plot of the O2 voltages and heat measurement we can nail this one down very quickly.

Frank

 

[Loober]

Yeah, me not knowing the difference between a monitor and a warning is probably part of the problem. There is no check engine light on, but the OBD shows a falshing C. The smog person said I have to drive it for it to clear, so that sounds like a drive cycle so I think what I am referring to is a monitor being set then. I was using the term warning to refer to monitor. So I guess my (C) monitor is not set. I hope it doesn't take 1000 miles! The DMV late fees are starting to add up already and with the price of gas that's like $362,958.27 total!!

So does Warning=CEL and Monitor=something flashing on OBD but no CEL?

Yes, if it is flashing then its not set, you need to find that magic window when all the monitors are set and the CEL hasn't lit and run to the smog shop. The 420 code is one of the toughest to solve because it can be so many things. Sometimes its minor enough where you have that window, other times its a problem you have to solve.

 

[Bud_Dude]

So did the smog shop fail you because of the warning even though you have no CEL?

From the description it sounds like the pre and post cat O2 sensors aren't reading sufficiently differently enough. If the truck passed smog with flying colors and the cats are heating up, I think taking a good look at the wiring would be next. I think if you can get a plot of the O2 voltages and heat measurement we can nail this one down very quickly.

Frank

In my case on my 2006 Dodge Grand Caravan, if the CEL light is on, it's an automatic fail, and since the smog machine is plugged into the OBDII port there's no way for the tech to bypass it. Brian at Brian's Automotive told me it would be the same case on my '97 LC. For the '95 he could let the CEL slide as long as all the tests are good, I gather this is because technically the '95 LC is not recognized as having an OBDII port...

 

[flyingmonkey]

I do. It's a blue tooth obd reader and you can build displays in your phone/tablet with the app. You can then watch values as you drive to see what might be going out of range. OBD diagnostics are set and cleared by the ratio of good / bad samples so you could have a part that's in range at idle but goes in/out under load. An 80 gets the high/low idle test so a scenario like that is very plausible.

This is the tool, it's actually quite cheap.. Amazon product ASIN B011NSX27A

Frank

I think I have one of these somewhere.

 

[Bud_Dude]

The app I use on my iPhone is called "Car Scanner" and works with generic ELM OBDII bluetooth modules. This app has a Smog test readiness mode that lists all the items that need to be cleared before heading to the smog shop.

Car Scanner ELM OBD2

Check what your car is doing in realtime, get OBD fault codes, car performance, sensor data and more! Car Scanner is a vehicle / car performance / trip computer / diagnostics tool and scanner that uses an OBD II Wi-Fi or Bluetooth 4.0 (Bluetooth LE) adapter to connect to your OBD2 engine management…

apps.apple.com

Looks like they have an Android version app as well... Car Scanner ELM OBD2 - Apps on Google Play - https://play.google.com/store/apps/details?id=com.ovz.carscanner&hl=en_US&gl=US

 

[RET2]

Ahh longing for the good old days.

 

[flyingmonkey]

The app I use on my iPhone is called "Car Scanner" and works with generic ELM OBDII bluetooth modules. This app has a Smog test readiness mode that lists all the items that need to be cleared before heading to the smog shop.

Car Scanner ELM OBD2

Check what your car is doing in realtime, get OBD fault codes, car performance, sensor data and more! Car Scanner is a vehicle / car performance / trip computer / diagnostics tool and scanner that uses an OBD II Wi-Fi or Bluetooth 4.0 (Bluetooth LE) adapter to connect to your OBD2 engine management…

apps.apple.com

Looks like they have an Android version app as well... Car Scanner ELM OBD2 - Apps on Google Play - https://play.google.com/store/apps/details?id=com.ovz.carscanner&hl=en_US&gl=US

Downloaded the app you mentioned and ran the emission/smog readiness test and the Catalyst monitor is still not set.

I'm not smart enough to know which gauges I should set on my screen to see what's going on or not going on. Any recommendations on what I should look at? O2 voltage or something? i have one of those laser temp things, next time I run it I'll measure the temp of the cats.

 

[elripster]

Yes, all 4 O2 voltages. If you can get a .csv or data out in some form I can analyze it.

Frank

 

[flyingmonkey]

Yes, all 4 O2 voltages. If you can get a .csv or data out in some form I can analyze it.

Frank

May have found at least part of the problem. The gauge for the 02S2 trim (B1) is not getting a reading. Does this info help develop a plan of attack? The free version only lets me pull two gauges, but I can pull the info the other )@ sensor if you need me to, but it seems to be functioning properly.

 

[elripster]

Yes it does. Where are these two sensors physically located? Like is one downstream of the other?

 

[flyingmonkey]

Yes it does. Where are these two sensors physically located? Like is one downstream of the other?

The O2 Sensors are located before and after the cats, so one is downstream of the other. I may be wrong but the chart I posted above is, I think, for the same O2 sensor. I am assuming that because the four gauges are named:

O2 Sensor 1 Bank 1 Short Term Fuel Trim
O2 Sensor 1 Bank 1 Voltage
O2 Sensor 2 Bank 1 Short Term Fuel Trim
O2 Sensor 2 Bank 1 Voltage.

So I'm assuming the one that is having an issue is the downstream (or second) one. Hope I'm not confusing things. I can take stuff apart and put it back together but when it comes to electrical I'm at a loss.

 

[elripster]

So reading up, the short term fuel trim should be +-10%. What I am reading is that a zero value is indicative of a bad cat. We can confirm with an IR thermo reading. If the cat is heating up then we are looking at wiring, sensors, if it is not then the cat is bad.

Frank