By on November 1, 2016


obd ii fault codes

TTAC commentator Igozoom writes:

Hi Sajeev,

I’ve been reading your postings for years and decided to actually share my (maddening) issues with you.

I have a 2006 Mazda3 S five-door (five-speed manual, 2.3-liter) that I purchased new in December 2005. It only has 101,000 miles on the clock but has had a few significant problems along the way despite regular maintenance. However, the most recent issue has me stumped.

Last week, I was driving home and ended up in gridlock. During this time, my check engine light came on. I did my old standby trick: disconnected the positive battery cable when I got home and the light stayed off after I reattached the battery the next morning. I’ve no idea what is causing the light to come on, but I’d really prefer to do everything I can if I can figure it out and fix it myself.

When I was researching an issue with my emissions test, I also read about another related issue: apparently, there’s a coolant temp sensor that’s prone to failure after the 10-year/100,000-mile mark. Should I start there first? The part is about $40 and it looks relatively simple to install, so I’m thinking about trying that.

Where can I start to look for the sources of these problems before I spend the money for a mechanic to figure it out?

Sajeev answers:

Igozoom, you seem like a cool dude and I thank you for reading my work.

Like I said over 6 years ago: forget about World Peace, everyone needs to talk in code. And it’s so simple.

Check it: a basic (engine) code scanner is dirt cheap and there’s an app for that. Or go to an Autozone type of place, that’ll generate code(s) for free. Once you get the code, Google it, research on a brand specific forum and email your boy Sanjeev Sajeev so we can give infotainment to the people.

And son, if you ever throw parts at a problem a la “the part is about $40 and it looks relatively simple to install, so I’m thinking about that” without an error code, we’re gonna have a big problem. You never, ever throw parts at a problem unless we’re talkin’ about this:

No such excuses exist today!

[Image: Shutterstock user mattcabb]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice. 

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33 Comments on “Piston Slap: Cracking the Code, Sans The (OBD-II) Code? (Part II)...”

  • avatar
    heavy handle

    Modern automotive diagnostics: read code, check forums. It’s a thousand times easier than it was in the old days: “she’s running rough, can you listen to the idle and tell me what you think?”

    • 0 avatar

      “Listen, you hear that?”
      “The hissing?”
      “No, that!”
      “Oh, the clicking.”
      “No, not that. Ah, it’s not doing anymore.”

  • avatar

    I think the letter-writer is kind of missing the point of all those indicator lights on the dash. The point of the light is to warn you there might be a problem. It’s not there just to test you to see if you know a secret trick to just shutting it back off.

    Pro Tip: In an age where we have OBD II, throwing random parts at a vague problem without at least starting with a scan is a terrible idea.

    No car should be without at least a cheap $20 scanner from Amazon. If you are stuck by the roadside, it’s the difference between asking a friend to pick up some minor part from the auto parts store and a tow to the mechanic. If you are at home… well there’s no excuse for not having one.

    (Odd Fact: Harbor Freight, despite being known for cheap tools, only charges slightly less than the even more-ridiculous price auto parts stores charge for scanners. The generic bottom-end (but perfectly adequate) 2-button scanner that’s $20 or so from any number of places on Amazon goes for $50 at HF and $65 at AA.)

    • 0 avatar

      Even the $50 Harbor freight code reader does freeze frame data. That’s the reason for the high price.

      • 0 avatar

        Or just get a blue elm obdii adapter, torque pro app for your android device and you’ll be set (and looking cool with dashboard full of fancy gauges). Also, it’s good idea to check your car when it’s new/in good running order to save a baseline readouts for different sensors (o2, fuel trim etc). This will help in any future troubleshooting. And google is everyone’s friend (if used correctly).

        • 0 avatar

          The base line for O2 sensors and fuel trim is the same for all cars. The O2 should switch between above and below .45v once closed loop has been entered and the fuel trim in theory should be close to 0% long term and fluctuating between +/- 5~10% short term.

          The big one you want to base line is MAF readings at various operating conditions. That is something that varies from car to car.

        • 0 avatar

          This. We troubleshot our E36’s oxygen sensor at a LeMons race with a plug-in one of my teammates kept in his truck and his Torque app. Put an OBDII adapter in each vehicle and load the app on your phone and you’ll never be without diagnostic capability.

      • 0 avatar

        There is a 20% off code for Harbor Freight online. Just Google “Valpak harbor freight coupon”. It’s good for months, and works on almost everything in the store.

  • avatar

    The guys who came up with the spec for OBD II codes assumed that people would try to game their emissions test by disconnecting the battery prior to the test.

    So disconnecting the battery is not a way to clear OBD II codes, all the learned setup info is lost and it never fixes the problem. Your car will now run like crap and the ready tags will need to be reset.

    VAG cars are particularly bad, some of them will barely idle.The throttle position indicator settings are lost when the battery is removed.

  • avatar

    If you want to fix your own car, a scanner is as necessary as a socket set or a jack these days. You won’t get far without one.

    Definitely check out the forums and see if you there is some brand-specific software available. Not only does the brand specific give you much better engine data, it also lets you access all of the dozens of other control units in a modern car. It will save you hours of time as well as the “parts dartboard” game Sajeev rightly dismisses.

  • avatar

    Even a proper engine code can send you off on a wild goose chase. Note – a real scanner with some software may have helped more than my cheap $20 OBDII one.

    For example my ’04 BMW 325i with 100k miles was getting a lean engine code. According to the forums, and reading I did online that’s most likely the intake tube – ie a vacuum leak after the MAF.

    So I replace the upper intake, which did have a rip in it. Cheap to do – only a $20 part. The engine code still popped up.

    Replaced lower intake – a real PITA job – and still got the lean code. This was luckily another cheap fix.

    Also checked the rest of the EGR tubing and couldn’t find anything wrong. Replaced the oil dipstick seal and the DISA seal since these are also known trouble spots. Not that expensive but still the check engine light would pop on.

    I ended up replacing the MAF since – according to what I read online – they can get “lazy” after so many years/miles. That still didn’t fix the problem. This was an expensive part.

    Longshot attempt that I read one of the the BMW forums – and the ultimate solution – was replacing the DISA valve. This closes/opens between the long and short runners of the intake. Mine was just flapping around and not opening at all, leaving me in permanent long runner mode. Why this popped a lean engine code I have no idea – but once replaced the check engine light went away.

  • avatar

    The ELM327 is a $15 OBD scanner that works with your phone.
    Go on Amazon or Ebay and do a search for ELM 327.
    iPhones use Wi-Fi. Androids us Bluetooth.
    Download any engine OBD app (I use EngineLink).
    You have access to your OBD codes now.

  • avatar
    87 Morgan

    Another Pro-tip….

    When the CEL pops on…swing by O’reilly Auto parts, AutoZone, any number of others on your way home from work and they will use their OBD-II (read…FREE to you) and run a scan. Then proceed to tell you what the issue is. In my case, I then go inside and buy said part and go home and YouTube how to replace it. The whole process typically takes an hour; my latest was the Bank 2 O2 sensor on my Suburban.

    Typically CEL lights are not to be ignored, especially if you consider yourself an enthusiast. Unplugging your battery is the bush league tactic of your overly cheap Uncle don’t ya think?

    • 0 avatar

      Its far smarter to get the codes from the parts boys, then Google it and check owner forums as our gracious author mentioned.

      Had it save me about $60 by not buying the wrong part (that the kid at AutoZone was SURE was the issue because of the code) on a V-8 Explorer one time. Turns out the most common cause for that code is not what is actually throwing the specific code. What threw the code (part “b”) was being affected by part “a” (the real faulty item), yet the kid at AutoZone never mentioned part “a”, only “b” which wouldn’t have fixed it.

      • 0 avatar

        Agreed. The parts guys three hour training gives them just enough knowledge to get themselves and others in trouble.

      • 0 avatar
        White Shadow

        Auto Mechanics 101: A fault code almost always points to the problem and not the solution. A solid understanding of the system is required to diagnose the problem and make the correct repair. If I had a dollar for every O2 sensor that was erroneously replaced by some dimwit with a scan tool, I’d be a very wealthy man.

  • avatar

    Definitely get the code scanned. I never understood people prioritizing just turning the light off at any cost (unless you’re about to trade it in), it’s trying to give you useful information! For what it’s worth I bet it is the coolant temp sensor (or even a thermostat going out?), my buddy’s ’06 2.0L had the same thing happen at around the same mileage IIRC.

    • 0 avatar

      I’m with gtemnykh on comments and diag. This guy sounds like he shouldn’t be allowed access to tools, needs to let it to the pros, or just lease every 3 years. Ham fisted repairs aren’t the way anymore.

      That said it is almost certainty the thermostat. Our 06 Mazda5 2.3 5MT thermostat failed at the 8 year mark, and our 08 Milan 2.3 FNR5 had its go bad just last year. These fail at a very specific mark, setting a coolant temp below threshold code.

      Use an OEM Motorcraft part only ($25-30 online), unless you like doing the job twice. Both the Mazda and Ford OEM parts are stamped FoMoCo btw, Mazda charges 35% more than Ford for the same exact part.

    • 0 avatar

      You make a very important point, that coolant temp sensor code could be an issue with the sensor or its wiring or it could be an actual cooling system problem. Having a scanner or app for your bluetooth link that lets you see live data is a huge step in figuring out what the actual problem is.

      For example the CTS or CHTS code could show that it is always cold. Park the car over night for a good cold soak. Next morning plug in the scanner and look at the Coolant/Cylinder head temp and compare it to the Intake air temp. The rationality check is that they and the ambient temp should be very close together. However if the coolant temp says -27 when it is 43 degrees out then there is an issue with the sensor or wiring. If on the other hand they match fire up the engine and monitor the cooling temp as well as the temp of the upper radiator hose, even just by touch. The indicated temp should rise to near the t-stats rated temp before the upper hose gets warm. However if the hose gets warm and the temp only says 120 then the t-stat is opening too soon.

      Using the gauge may or may not be of any help. It could be driven by a coolant temp sender or the coolant temp sensor and filtered by the PCM. Many cars have idiot gauges for the temp. So it may show the same reading for a wide range of temps, ie 170-210 could all cause the gauge to have the same reading.

  • avatar

    Last April my Impala’s CEL came on. I cleaned the gas cap to no avail. I went to Advance Auto near me and had the OBD ll scanned. Something in the emission control system, but no real detail. I took it to Chevy and they eventually found out it was a purge valve. Was I able to isolate that problem I probably could have replaced it myself, but wasn’t going to throw parts at it.

    Earlier last year our Honda CR-V had the CEL on and all of a sudden it would lurch and surge causing a real safety and driveability problem. We drove it home, she got in my car and she followed me to the Honda dealer and we left it there with a note. Can’t recall what the problem was exactly, but it was serious enough to take care of it immediately.

    Don’t ignore CELs!

    • 0 avatar

      The last time I dealt with a CEL anywhere was a Corola that (thanks, code reader and internet!) need the airflow sensor cleaned.

      Coulda driven it safely for, probably, months.

      On the other end of the spectrum, the last one that happened while I was driving was when the 5.4 in my SuperDuty killed stele with total compression loss on one cylinder.

      There was no disguising that that was *serious* “pull over now and shut it off” problem…

  • avatar

    Never clear a check light w/o checking the code and looking at the freeze frame data which is valuable in determining the actual operating scenario that caused it to set the code. Knowing the situation that caused the code to set allows you to actually verify if the repair fixed the problem.

    Another important note about check engine lights is that if it comes on solid, drive on and investigate later. If it is flashing get off the road and shut down the engine as soon as it is safe to do so. The light flashes when there is something that could do permanent and possibly major damage. The most common reason for a flashing light is a dead cylinder. That means the exhaust can be getting filled with fuel. That fuel will at least partially burn in the cat potentially raising its temp to the point it can cause a fire. Some systems are smart enough to shut down the injector on that dead cylinder to prevent that problem while others are not.

  • avatar

    If you go to a parts store and have them pull the codes, dont buy the part the recommend right away. Go research it online as Sanjeev suggests. The parts stores typically use the generic issues while some manufactures change the meaning of the codes to represent different issues.

    • 0 avatar

      The generic codes are not changed by some mfgs, though the recommended diagnosis tree will be different by mfg. Mfgs have their own codes denoted by being a P1xxx, instead of the generic P0xxx, and those meanings are specific to each mfg. The reason you don’t just buy a part is because the cause of the code may be an operating problem not a sensor problem. See Coolant Temp Sensor vs Thermostat above.

  • avatar

    I’m currently working through a CEL thing, a P0717, turbine input (speed sensor) problem on my wife’s ’08 Sienna. Light has been on-off-on again for three months. I’ve had the code checked twice at VatoZone, to make sure it’s always the same code (it is). Pulled the battery and other stuff out of the way (it’s on top of the transmission), and checked across the pins on the sensor with my DVOM, and it’s shot. Supposed to be 560-850 ohms, got infinite resistance (open). Light is still on-off, but I ordered the part yesterday (I could get the Toyota part online for same price as aftermarket part from VatoZone), and it should be ready to pick up in a couple of days (local Toyota dealer who sells on Internet).

    And yes, just disconnecting the battery causes its own problems. Once reconnected, it took a little while, a little idling, and a little driving, before the idle came back to normal (it started off at 400-500 rpms). Plus having to reset the clock, the radio stations, and the auto up-down on the driver’s window.

  • avatar

    I have an ELM 327 Bluetooth and Torque on a Galaxy Nexus phone I keep lying around (not as a phone anymore). On my 1998 Camry, I kept getting a p0136, O2 sensor issue. I was thinking that is the one on the exhaust, and it’s a pain to get to, so I kept clearing the code and waiting for it to come on again. Recently, my exhaust pipe came lose of the muffler. Took it to Ralph’s Muffler Shop here in Indy, and sure, they can fix it, but come look at this. Someone had patched the pipe with a plate and some weld. it was leaking. They took that out and replaced and reattached to the muffler, and haven’t had the code since.

    • 0 avatar

      I hear good things about Ralph’s! Cool to see a fellow old Toyota driver in town :)

    • 0 avatar

      Yup an exhaust leak up stream of the O2 sensor can cause O2 sensor related codes. Fact is the pulses of the exhaust can actually suck air in just as it lets exhaust out. That extra O2 messes up the O2 output and can cause all sorts of problems. It usually takes a big toll on MPG as the computer richens up the mixture in an attempt to get a rich reading.

  • avatar
    SCE to AUX

    It also helps to know something about how an engine and its sensors work together.

    My former Scion xB1 would trip the check engine, traction control, and vehicle stability control lights all at once. This was a rare and seemingly random event, and it did not affect driveability.

    Once I viewed the actual data on my OBD-II computer, I noticed that the voltage coming from the downstream O2 sensor was always stuck at 0.075 V. [O2 sensor voltages should be dynamic, and are typically higher than this.] After replacing the downstream O2 sensor, the problem never recurred. Driveability wasn’t affected with this fault because it’s the leading O2 sensor which controls engine performance; the trailing sensor simply monitors the performance of the catalytic converter.

    The codes collected by my code reader would have led me down an expensive bunny trial if I didn’t understand how a car actually works. None of them indicated an O2 sensor problem.

  • avatar

    2015 Golf R, started but ran very rough the other day, missing a whole cylinder kind of rough.

    I do have (not cheap) PC based code reader/diagnostic software, so I ran the codes: cylinder #2 fuel injector circuit malfunction. Now this is a direct injection engine whose injectors and much of their harness are buried someplace inside the cam cover. Nothing is going to be done by me while it’s under new car warranty.

    Had it flat-bedded to the dealer. Next day they call and tell me that rodents have eaten my injector harness. When tech pulled the belly pan there was a cascade of nuts, acorn and miscellaneous plant material. WTF!!!!

    So on the plus side the fault code was absolutely correct. On the minus side this isn’t covered by warranty and ran me $750 out of pocket to fix. Sigh.

  • avatar

    Don’t feel bad, same thing happened on our 1-year new ’96 Crown Vic.

    Rats just loved the ignition wires, chewed through 3 of them. They took some dog kibble up on top of the valve covers with them and enjoyed the wires as a dessert.

    Ford must have mixed peanut butter into the insulation somehow, resulting in a new spin on Panther Love.

    Not Warrantied in my case either…120 bucks for a set of wires.

    • 0 avatar
      White Shadow

      You’d probably be surprised to learn how much research and development has gone into electrical wire (specially the insulation) in recent years. I work in the plastics industry and I can tell you with certainty that some of my customers, like Southwire, are a major supplier to many OEMs and they’ve been working on non-soy based automotive wiring for quite some time. Rodents obviously love the soy stuff.

    • 0 avatar

      The wiring in Subuarus from the 80’s and early 90’s was apparently quite tasty to squirrels. A coworker of my wife had the problem many times with their Subaru. On the old show My Name is Earl there was an episode when Joy says that the Subaru is in the shop, damn squirrels ate the wiring again.

      I’ve never had a problem with any of my Panthers but one morning my wife went out to go to work in her Fusion Hybrid, and as she pulled out of the driveway she could tell it was missing bad and of course the CEL came on. She turned around and took another car to work. I went out there later and the scan tool showed a miss on #3. I pulled the top cover and found no wiring left between the bundle and the connector for the #3 coil as well as a few tooth marks on the connector.

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