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My 2006 Toyota Tacoma had a check engine light, which I decided to try to turn off for the purposes of vehicle inspection. I thought that was okay because the problem was not emission-related but camshaft. I did it right before going to the inspection station. I thought this might work because I had previously turned the check engine light off by resetting the ECU and it stayed off for some time (until the ECU got enough readings, perhaps?).

The inspection detected that not all monitors are ready (Catalyst, Evap Sys, O2 Sensor in particular, none of which I understand had to do with the previous check engine light) and the guy correctly guessed that I had reset the ECU by disconnecting the battery. He said the truck needed to be driven some for all the monitors to become available.

I just drove the truck 70 mi, and thought the monitors should be available by now, especially because I plugged my own OBDII reader, which reported no codes but also didn't report unavailability of monitor reading, which I took as a likely indication of readiness. I took the truck to the inspection station and it failed again, for the same reason. I am not sure why the inspection station's OBDII reader is more sophisticated than mine, perhaps because I got mine for $30 from Amazon and it doesn't detect sensors not being ready to report status. Even though I hadn't fixed the code that cause the check engine light, the light has not returned yet, maybe it will once the monitors become available. I was really hoping that all the emission-related monitors would become available but not the ones that cause the check engine light, which would provide me a window of opportunity to pass inspeaction.

Q1: Is there any way for me to induce the reading on these monitors without being at the mercy of an undetermined number of miles before they are available? If not, any idea how many miles need to be driven?

Q2: Is there a way for me to know, like the inspection station knew, that they are available so I don't go before?

Q3: Will the inspection fail me if the check engine light is on but their OBDII reading indicates the code(s) are not emission related?

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    Probably need 100+ miles. – narkeleptk Jan 2 at 20:12
  • Is there a way for me to know, like the inspection station knew, that they are available so I don't go before ? – amphibient Jan 2 at 20:13
  • Maybe this site can help. I don't recommend the software or tools but the information on the page is not bad. obdautodoctor.com/scantool-garage/… – narkeleptk Jan 2 at 20:16
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    @narkeleptk, raw distance isn't enough. You also need to drive in a variety of conditions (eg. highway driving, stop-and-go traffic). – Mark Jan 3 at 5:57
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Q1: Is there any way for me to induce the reading on these monitors without being at the mercy of an undetermined number of miles before they are available?

Basically, no. Every OBDII compliant vehicle has included in their software a feature called a drive cycle. Your vehicle won't show the different emissions related things as ready until the vehicle has completed the drive cycle. There is only one way I'm aware of to get around this and that's by having an aftermarket tune applied. This is not something which is cheap to have done (for most people), and isn't something which most anyone can do.

Q2: Is there a way for me to know, like the inspection station knew, that they are available so I don't go before?

Sure. Most OBDII scanners have the emissions checks built into them. Even a ELM327 Bluetooth device using the Torque Lite app can tell you this.

Q3: Will the inspection fail me if the check engine light is on but their OBDII reading indicates the code(s) are not emission related?

In most cases, yes. I can't say this is true for everywhere, but I know it's pretty standard for an emissions station to fail you right off if the CEL is lit. No ifs, ands, or buts.

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  • RE: Q2, since my OBDII scanner does not provide that info, should I look for a different device? – amphibient Jan 2 at 20:47
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    @amphibient - That is the main purpose of most OBDII scanners, I'm surprised yours doesn't have it. Like I was saying in the answer, an ELM327 Bluetooth would give you that availability. You can get them off of eBay or Amazon for under $20US. Torque Lite is free (yah, has ads, but it works for this purpose). – Pᴀᴜʟsᴛᴇʀ2 Jan 2 at 20:49
  • @amphibient - I have this one. Used it many times without issue. it works with Android devices. If you use an iOS device, you need one which is wifi enabled. – Pᴀᴜʟsᴛᴇʀ2 Jan 2 at 20:51
  • The drive cycle requirements vary by make, model, and year. Certain tests require the tank to not be too full or too empty. A certain number of cold start cycles etc. It can take quite a few miles to complete all the requirements. – mikes Jan 2 at 21:16

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