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Normally, when I read my '07 Hyundai Sonata, the reader takes about 10 seconds and then returns "0 Codes" (or whatever).

However, I just was checking out a 2010 Sonata. I hit Read and it popped up "0 Codes" without even a millisecond. I'm concerned that the seller may have either spoofed the OBD system or that it's simply broken.

Is it normal to get a reading that fast or should I suspect some problem with the OBD system itself? (The reader still works fine on my 07).

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    Does your reader do live data? If so, it'll let you know it's either working and reporting data or not. – Pᴀᴜʟsᴛᴇʀ2 Nov 3 '16 at 15:54
  • I'm not sure wha that means--but the reader is a cheap one, under $50. So if live data is a high-end option I'd have to say no. – jimo3 Nov 3 '16 at 17:03
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    3rd option... your cheap code reader is incompatible with that vehicle. Try autozone or a parts store that will scan for free to compare. – cory Nov 3 '16 at 17:51
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I believe I found the answer. The reason my (very cheap) reader instantly read "0 Codes" was because the seller had temporarily disconnected the battery cable prior to my test drive and me testing the OBD. This resulted in no "ready" systems, so it instantly read 0 codes--because none had the sufficient driving time to accurately interpret the reading.

Unfortunately I found this out after the fact (i.e, after I'd been "taken" by the dealer) when I bought a better OBD reader and saw that the "Cleared" time read 2 1/2 hours--exactly the time I called the dealer telling him I'd be in to take another look at the car. The new read showed that there were not-ready systems (I guess it takes a couple cycles of driving for an hour or so--so the dealer would disconnect the battery before every test drive), but I had the old cheap OBD prior to the purchase.

So--lesson learned--if you're buying a used car an notice the radio has none of the stations programmed--and maybe the clock is showing 12:01 when it's 9 Pm--then it's very likely the battery cable was temporarily disconnected to deliberately clear all systems to the not-ready state so they read no error codes. In my case, I think I've got a bad Cat, so not cheap--but at least the car runs very well and I'll have to live with an engine light until the next emissions test.

My takeaway--spend a few bucks more on a reader that will tell you when it was last cleared, or--if you have a cheapy OBD like I did--if it instantly reads "0 codes", that probably means the systems are in a not-ready state so beware. --Jim

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Try disconnecting a sensor (mass airflow sensor is my favourite), start the car and idle it until the check engine light comes on, then read the codes.

It's pretty difficult to hijack the OBD system, most people would just remove the bulb for it to make it look like there's no codes.

  • Wouldn't the car stall when you disconnect the maf senesor? my 1993 miata stalls – method Nov 3 '16 at 21:04
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    @method Different cars have slightly different setups regarding the MAF. In the absence of a signal, mine assumes part-throttle, just to get you home. Some cars will need you to give some throttle to keep the engine alive in this scenario, but the ECU should find out about the MAF being disconnected and throw a code. – tlhIngan Nov 3 '16 at 21:23

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