P0446 - '99.. Z71.. 5.3.. 4x4..293k

[MikeD268]

So I failed emissions with this a few weeks ago. Also came up with bad O2 sensor. Shop can't tell me which sensor failed so "go across the street to my brother's shop and he'll pull the codes for you." Short story, NO codes show up for brother. No CEL either.

Few weeks later, 0446 pops. NO O2 sensors, just 0446. Replaced the purge solenoid as it was an easy $25 shiggle and it was still OE. Didn't solve so I crawled under and found that the breather hose on the vent solenoid had kinked an inch from the connection. I had replaced the entire canister 3-4 years ago.

So I rerouted the hose and strain-reliefed hoping to avoid future kinks and cleared the SEL by pulling the ECM fuses and discoing the battery. Hose wasn't clogged at all otherwise. Now I'm just waiting for 200+/- miles to roll by to see if it solved the problem.

I've got a set of O2 sensors ready to go in, just in case, but until/unless I can identify which are throwing the code I'm just guessing as to which to replace. Any thoughts/guesses as to whether unkinking the hose will potentially solve either/both the 0446/O2 sensor fails?

[maxwedge]

The evap code can take a whilebefore popping up as the monitors must reset. The o2 sensor code always pinpoints the specific sensor when read with a scanner.

[j cAT]

Originally Posted by MikeD268

So I failed emissions with this a few weeks ago. Also came up with bad O2 sensor. Shop can't tell me which sensor failed so "go across the street to my brother's shop and he'll pull the codes for you." Short story, NO codes show up for brother. No CEL either.

Few weeks later, 0446 pops. NO O2 sensors, just 0446. Replaced the purge solenoid as it was an easy $25 shiggle and it was still OE. Didn't solve so I crawled under and found that the breather hose on the vent solenoid had kinked an inch from the connection. I had replaced the entire canister 3-4 years ago.

So I rerouted the hose and strain-reliefed hoping to avoid future kinks and cleared the SEL by pulling the ECM fuses and discoing the battery. Hose wasn't clogged at all otherwise. Now I'm just waiting for 200+/- miles to roll by to see if it solved the problem.

I've got a set of O2 sensors ready to go in, just in case, but until/unless I can identify which are throwing the code I'm just guessing as to which to replace. Any thoughts/guesses as to whether unkinking the hose will potentially solve either/both the 0446/O2 sensor fails?

with the O2 sensor as was mentioned this will throw a code and the CEL will be ON ! However if the O2 sensors are 300K miles on them then replace them.

on the canister EVAP system. this is a problem will over filling the fuel tank then parking the vehicle with out burning off the excess fuel you do this too often then those evap hoses get fowled with charcoal crap that then messes up the venting solenoids ..

these vehicles throw codes very quickly and often if anything is off just a small amount. if the PCM sees anything wrong the CEL will come on !!

so what is the reason your vehicle failed the emissions test. no CEL so you have a PCM that was reset / battery disconnected ??????

[MikeD268]

Max, truck was read by "brother's" station with - what I can only ASSume was - a "professional" OBD2 reader. Brother didn't see any O2s or 0446 for that matter. Had VIP pull codes, as well, once the CEL came on. VIP didn't see any O2s. "Brother's" code reader looked beefier than VIP's fwiw.

j c, reasons I got flagged:
OBD Inspection Results:
*Check Engine Light*
- Engine Off: Instrument Panel Illuminated Properly: Passed
- Engine Running: Vehicle's OBD Computer(s) Reported Check Engine Light was not Commanded on: - Passed

Readiness Monitors
- Misfire: Ready
- Catalyst: Not Ready
- EGR: Ready
- Fuel System: Ready
- Heated Cat: Unsupported
- Air Condition: Unsupported
- Air System: Unsupported
- Heated O2: Not Ready
- O2 Sensor: Ready
- Comp Component: Ready
- Evap System Not Ready

Def planning on replacing O2 sensors. I've only got one set (up/downstream) at the moment, though, and want to replace the known offending part first. I just don't know which bank it gone and no one can seem to tell me.

[maxwedge]

You can see the evap monitor is not online that is always the last one to activate. The heated part of the o2 sensors is also not ready, I would wait till all are back before doing any repairs so you are not blind and just replace parts, agreed at 300k the o2 sensors are degraded.

[j cAT]

SO as I ASSumed your PCM was not ready . your O2 sensor heated test did not complete. your vehicle like my 2000 will pass with only ONE unready you have TWO unready...

EDIT: you had 3 unready tests ,only one not ready allowed to pass !!!

[MikeD268]

OK... At least driver's side O2s got replaced before dark/rain set in. It's probably me, but the truck seems to have a little more throttle response to it now.

I'm going to guess that the monitors/systems they watch key off of each other. Any chance that replacing the O2s may solve all of these fails?

j c, I may be SOL up here in NH. OBD Safety says that if any one system fails the truck fails. http://www.nhinspect.com/whatToExpect.html I'm crossing everything I can that, as usual, you know something I don't about year specific pass/fails.

Just searched through the forum and can't find any info on the proper drive cycle for this truck. Any suggestions?

[j cAT]

operate the vehicle for 5-10 miles each day with the engine temp in the normal range. do hywy and back roads .. in 3 days the readiness should be done so that you will have only one readiness not completed which I have found is the evap test. keep fuel in the 1/4-3/4 tank amount.. replacing these O2 sensors what will happen is you will feel better throttle response because the O2 sensors report the fuel mixture faster when new/clean !!! also you will gain on the MPG.. I got 18 plus MPG going up to north conway and back to mass....87 octane.. sometimes it may take a week of driving to get the readiness to be completed. I have had a P0300 code 4 times in 14 years very random and with my code reader/reset tool I have found at times it will take a week. then if you remove the battery for some reason this will also mess up the readiness of the PCM to pass the emissions test. with a cheap 80 dollar tool you can check all this and not have to bother your family member to see if its ready. these tools work on most all OBDII vehicles look for the actron CP9125 pocket scanner ..works good .. cheap fast ..

[maxwedge]

In NYS, you can pass with one monitor not online as long as no cel/codes.

[MikeD268]

Thanks for confirming the throttle response for me, j c. I figured that's what was happening. At least I'm not COMPLETELY crazy in thinking that I felt it.

Thanks for that Actron scanner, too. Found it on Sears.com for all of $30. That'll be going in the toolbox ASAP.

[rkvons]

One distinction you should make though, is the difference between a 'Failure', and a 'Not Ready'. A failure will light the CEL. A not ready will not. You should never clear a code from the OBD system. This clears all the monitors. The CEL light will go out by itself when the problem goes away. It is much better to have all the monitors ready and the CEL light on and then go out to show the problem went away, then to have all the monitors not ready, code cleared, and wondering if the CEL light will light again, in my opinion.

[MikeD268]

Well this is interesting... After replacing just driver's side (Bank 1) up and downstream O2s I found a drive cycle suggestion here: http://www.lyberty.com/car/drive-cycle.html Followed it and within 10 minutes of completing the CEL came on again. Had the code pulled and instead of the 0446 I'm getting just a P0430 Bank 2 code. Hopefully, I'll have time this weekend to get the passenger side O2s replaced.

[j cAT]

Originally Posted by MikeD268

Well this is interesting... After replacing just driver's side (Bank 1) up and downstream O2s I found a drive cycle suggestion here: http://www.lyberty.com/car/drive-cycle.html Followed it and within 10 minutes of completing the CEL came on again. Had the code pulled and instead of the 0446 I'm getting just a P0430 Bank 2 code. Hopefully, I'll have time this weekend to get the passenger side O2s replaced.

the 430 DTC is the passenger side cat converter code. this is caused by an O2 sensor or because of a bad converter. this type code takes a longer amount of drive time to pop up for the readiness .. some have had the PCM reset and drive a couple of days to get the readiness monitors to pass on all except the cat test. then with one missing pass then a day or 2 later the 430 may return.

using higher octane and a fuel additive to clean the converter has helped some get over this 430 code.

walmart has CRC guaranteed to pass for 12.00 . some have had success with this along with using the 93 octane.

[MikeD268]

Alrighty then. Finally had time to replace the passenger/Bank 2 up and downstream O2 sensors. Caught a deal on parts too and only paid $68 for both sensors. Turns out that O2 sensors affect the P0446 evap emissions issue among other things. Big box confirmed that no codes were being thrown after all sensors were replaced. Now to get the final word from the inspection station once the world opens up for business again next week. Will update once that happens. As I've replaced the evap canister/valve in the past, specifically to get rid of a P0446 - and it didn't work, in hindsight most likely due to dead O2 sensors - I highly recommend checking the functionality of your O2 sensors before replacing the canister. Might save you a chunk of change as the canister cost me $185 from the dealer a few years ago. Canister is more of an involved process to replace than the O2 sensors as well.

[MikeD268]

Passed inspection clean. Zero codes thrown. So one of two things rectified the P0446 - fixing the kink in the evap canister breather hose or replacing the O2 sensors. Unfortunately, I didn't test between rerouting the hose and replacing the drivers side sensors.

Toughest part about replacing them is a.) breaking them loose and b.) unclipping the wiring harness. For a.) - a little PB Blaster soaking for a minute seemed to ease things and b.) try to replace them when the plastic is relatively warm and clips are functional. Working with cold plastic is just a SNAFU waiting to happen.