iPhone app get 1999 suburban codes

“Check engine soon” (not ‘now’ or just plain check engine) light. Similar instance ~3-5 months ago. Mechanic read codes said not to worry the problem (forgot now) not important and costly. He said to wait until other work needed. Since this time is likely same as last but can’t be sure, if I could get the codes myself, look them up I wouldn’t have to bother the mechanic whenever the light decides to flash. Is their a recommended app that comes with a connector that would serve my purpose?


Google would be a fine app to find auto parts stores. Easier to go to an auto parts store that reads codes for free.

But for anyone to read the code I need to get the codes which means I need the app + connector and that’s what I’m asking advice on.

Have you seen this?

“But for anyone to read the code I need to get the codes which means I need the app + connector and that’s what I’m asking advice on.”

Can you get that app and connector free-of-charge?
I ask because “Free” is the policy at Auto Zone, Advance Auto, O’Reilly, and (possibly others auto parts stores) for having them plug-in their code reader and give you the codes that they found.

I don’t understand your problem. any parts store, as stated, will read the codes and give you a printout of the numbers. You can look the numbers up online for more info.

If you want to buy a code reader, those are relatively cheap. $15-20 for a basic model. Then with the number, again, you can look up the meaning online.

Yes, you can get a special connector that will interface to a smart phone, but that can be expensive.

“Yes, you can get a special connector that will interface to a smart phone, but that can be expensive.”

I used to have a boss who liked to do everything in the most complicated way possible, rather than the most efficient way. I used to say, “If Jerry was a surgeon, he would do sinus surgery by going through the soles of the patient’s feet”.

So…yes, the OP can buy a specialized connector and can download a code reading app to his phone (which will likely cost a few bucks), or he can opt to buy one of the many inexpensive code readers, or he can simply go to an auto parts store where he will pay ZERO for this service.

I believe that markg2 defines “read the code” as interpreting the code. He now has more answers and opinions than he probably expected.

Good luck, markg2!

Thanks guys I didn’t know parts stores would plug in and read the codes–for no $.


Okay, now that you are aware of this reality, please return to this thread once you have obtained the codes, and some of us will attempt to give you further advice.

Please bear in mind that none of the codes automatically = “replace xxxxxx”. There are often alternatives to throwing parts at a problem.

I’ll be back.

The code is P0420. This must be the same code that the mechanic said he read ~4 months ago since (now I remember) he had said the problem was most likely the oxygen sensor. He said the sensor was expensive to fix and not any cause for alarm and don’t bother fixing until something else important goes south.

After reading various posts on a Google search, it looks like the problem could be almost anything related to the catalytic converter system?

Although it’s my wife’s car and I drive it seldom–like yesterday taking it to NAPA, I do not sense any significant loss of power or irregular engine functioning.

So it would appear that the only important reason to fix the problem would be in advance of her next emission inspection–which she’ll fail absent a fix.

So that’s my relatively uninformed take. Now, what do you guys have to say?


P0420 Catalyst System efficiency below threshold (Bank 1).

Could be either a bad O2 sensor ($100), or a bad cat ($600), depending on where you buy parts. Those are typically what’s wrong when you see that code.

Bank 1 should be the passenger side of the vehicle, and the O2 sensor in question will be after the cat.

As a test, and if the wires are the correct or same lengths, you can swap the left and right sensors. The system should, after a time, reset the P0420 code and throw a P0430, which would tell you the problem is the sensor.

If that CEL isn’t flashing, then it’s an emissions issue, and other than costing you some mileage, you can continue driving. If it’s flashing, then it’s more serious, and it needs to be looked at right away.

You can get a free app for your phone that reads codes and does a few other things as well. Use the link supplied by another poster or search wherever you get iPhone apps. I’m an Android guy and there is a free on for us, Torque. It also allows you to record data.

To get the signal from the car to the phone you will need a bluetooth obd II adaptor like this
You can buy this from Amazon and others for about $9. That’s almost free.

If you chart the O2 sensors you can see if they are lazy or failed without having to take them out and swap them side to side although that is still a good idea to check to see if it is a wiring problem.

I agree with @chaissos. The O2 sensor fault you see is a downstream sensor that is bad or the cat for that side is bad. Neither will keep the car from running properly but both will fail an emissions test. A bad cat will spew pollutants into all our air for us to breath. Your call there.

However, if the upstream sensor is fluctuating much slower than it should . . . because it’s gotten old and sluggish, as we are . . . that could result in a P0420 code

P0420 is generated when the downstream sensor fluctuates at nearly the same rate as the front. A faulty downstream sensor, which is fluctuating too fast, could also result in P0420

I agree that switching sensors side to side, to see if the problem moves, would confirm or disprove the bad sensor, without spending any money on parts, prematurely

A worn out/bad cat, which takes too long to warm up and do its thing, or just isn’t working at all, could also result in P0420

If the cat turns out to be the problem in the end, you might want to consider if it failed as a result of something. Such as misfires, excessive oil consumption, overheating, etc.

“Works with all OBD-II compliant vehicles”

Is our '99 Suburban compliant?



A quick visit to Amazon and it seemed that Android compliant scanners were in the $9 range while iPhone scanners were several multiples in price.

Then I found this one: Xseries Auto™ WIFI Wireless OBD2 Auto Scanner Adapter Scan Tool to Check Engine Light & Diagnostics for Iphone6, Iphone 5S,5 Ipad IOS PC and Android(Black) on Amazon. I’m suspicious only because it’s the only device I’ve seen so far that says it’ll work with both an Android and iPhone?