California Smog - Stubborn Issue

1996 Tacoma, 3.4L, manual. 365K miles, original engine

I’m having trouble getting my rig to pass California smog inspection. It’s failing with cat and evaporative readings. It’s also giving erratic coolant readings even after I’ve replaced the engine coolant sensor.

I’m working with a well respected local shop with a good reputation. This is what I’ve tried:

• Multiple completed drive cycles, followed to spec
  
• Premium gas
• Replaced coolant sensor
• Three tests / retests, the last one 220 miles after the previous one

Mechanic said we should drive cycle one more time before we determine that it’s an electrical/computer problem and think about replacing the ECU. Anyone encounter a similar problem and come up with a solution? Thanks.

 

check the plug and make sure its in working order.

Couple years ago I went to 3 different smog shops trying to get my truck to pass inspection for registration renewal. 1st two were quick smog places that couldn't get it to read correctly/pass, the last shop was my regular offroad shop I took it to and they discovered some of the plug connections were going bad and it needed to be fixed, then it passed inspection perfectly.

otherwise, idk. never had a car fail to pass smog outside of that.

 

Do you mean *spark* plug connections? Thanks.

 

No, the actual OBDII plug and it's connectors in this scenario

 

Gotcha. Do you know how they repaired these connections?

 

Are you getting a check engine light with codes? If so, what are they?

 

Nope, no engine light or codes.

 

Did the smog place give you a printout of the fail? Does it contain any details? Also, when you say "premium gas", does this mean you're using 91 Octane?

 

tbh no idea, I'm not electrically inclined at all. My shop just said they had the same issue as the other smog spots, got into the footwell, and saw some of the wires hooked up to the plug were fraying or pulled out. I believe they just repaired the connections and resealed them, but I can't say for sure :/

 

You might check the post cat o2 sensor if the cat itself isn't the problem. Emissions are not excessive?

 

I did get a print out of the fail. I pass on visual and emissions, but I get a fail on "functional check" for "OBD systems". Specifically, the catalyst and evaporative system statuses are listed as "Not Completed". Additionally, as I mentioned the engine coolant temperature reading is erratic.

 

You could have a system voltage issue. Is your battery holding a full 13 or so volts? If you are below 12, the system voltage could be the issue. All those sensors work on resistance and low voltages, and low system voltage can create sensor reading problems. I would begin by checking all connections and grounds, then the alternator output and battery voltage. The alternator and battery can be checked by Autozone. Check the integrity of all the sensor wires and plugs.
The evaporative issue can be anything from a gas cap seal to your vapor recovery system. The vapor system can be a vacuum line, a port, or the recovery canister. I would start by looking through you tube aor with a general internet search to see if there is a common problem with any of these systems.,
Check the cleanliness and integrity of all the connectors, the voltage issue, and then go through the evaporative system. If you keep going back and failing, California might label your car as a "gross polluter". I'm not totally sure since it passed the emissions, but either way, it could become problematic and itgets recorded by Carfax.

 

I had this issue with the catalyst monitors not setting to "ready" for smog. I drove hundreds of miles and did the FSM procedure several times to no avail.

What got mine to work was putting a can of Cataclean in the fuel tank then driving around some backroads in 4lo for a few miles ... monitors went from 'not ready' to 'ready'. I have an obdii scanner so I can monitor when they go green.

It's actually happened to me twice when getting smogged, and both times Cataclean and 4lo did the trick

 

I should mention I had no issue with the evaporative system status monitor, just the catalyst one

 

https://www.youtube.com/watch?v=BuZYAy_xi0E

 

Update for 4/3/24

• Used Cataclean as per instructions, drove through 1/4 tank with it, refueled. Bunch of those miles were in 4WD low gear
• Ran the truck at 3K RMPs on local roads by running in a lower gear for 3-4 minutes (I have a manual)
• Tested the battery, running perfectly fine voltage (almost 14V running, 12.9 not running)

Still getting incomplete readings for both cat and evaporative via OBDII. Wondering what my next steps are...

 

I would think your 02 sensors may be dying as far as the Cat issue. The evaporative will be a process of elimination. If the smog station checked the gas cap and it was okay, I would go over the vacuum lines and look for cracked and loose fitting lines. Then, I would check any check valves or vacuum switches and follow the lines all the way back to the canister. any cracked lines or a cracked canister will create a problem. The best way is to smoke check the system for leaks, but you will have to pay someone to do that unless you have a leak checker.

Have you cleared those faults after you have made changes? Sometimes they won't clear automatically. If you cannot clear them, disconnect the battery, give it few minutes, reconnect, start, let it idle for a few to relearn the idle strategy and get up to temp, then check it. Remember, if you clear info, or disconnect the battery, you need to drive it a day or so before having it checked again, or it will be failed.

The thing about this stuff is it is one worn or leaking part that is causing the problem. It's just a pain in the butt to find that particular part in a sea of parts.

Once the problem is resolved, tell us what did it.

 

@CPS-65 thank you for your feedback. Just to be clear, I'm not getting error codes that I can clear. I get INC (incomplete) for evaporative and catalytic, which I don't believe can be cleared unless I am mistaken. I just need to solve for one of these incompletes, as California let's you pass smog if one is incomplete, but not both.

 

Okay, I see. I think I would still disconnect the battery and let the computer go through and query all the sensors. I hope you can get this thing resolved, smog stuff can be a real pain but there is no getting around it.

 

Not fun. I recently had a nightmare on my 2nd Gen.

Youve done a lot so far. But have you given it the Italian tune up? Put a bottle of techron in half a tank, get it nice and hot my going full throttle on some straight uphill onramps multiple times. It will cook off carbon deposits.

In my case, it was a voltage issue on the OBD connector under the dash. They couldn't even connect for the test. I also had a few shot fuses. Use a fuse tester on every singlemone under the hood and under the dash. That did fix it, but I did catch several future problems.

I ended up buying a new OEM connector and repinning all connections. That fixed it right away. If you want more info I'll dig it up.