# My car's" Check Engine" light: Has the sensor gone haywire? **URL:** \ **Category:** Factual Questions\ **Created:** [September 1, 2014, 7:43pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183 "2014-09-01T19:43:02Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [September 2, 2014, 10:03pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/21 "2014-09-02T22:03:34Z")
> [@kaylasdad99](#): > > What does OBD mean? > > And OP, the Midas shop in Anaheim has a sign saying they’ll diagnose your “check engine” light for free. It’s likely you can find a place locally that will do the same for you. This mechanic has serviced my car for years. He’s a nice guy. A large repair facility really wanted to take me for a ride (with a slew of repairs they said my car needed after an inspection–done during a discounted oil change they advertised–but my mechanic said at least half of those repairs were unnecessary ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [September 2, 2014, 10:09pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/22 "2014-09-02T22:09:30Z")
Since this is an OBD-I car, you don’t need a scanner. With Ford’s system, there’s a diagnostic port with a bunch of pins (where you would plug the scanner in if you had one) and a smaller single wire connector. You just need to jump the single wire connector to one of the pins on the diagnostic connector and then turn the key on and the CEL will blink the codes to you. Here’s an explanation: [Ford OBD/OBD2 Codes – TroubleCodes.net](http://www.troublecodes.net/ford/) Ford’s system let you do some other fancy self-diagnostic stuff, but to get the codes all you need is the single jumper wire setup in the bottom “Hook up for MIL…” pictures. Alternatively, if you punch something like “Ford OBD1” into youtube you’ll get a bunch of videos showing how to do it. > [@Rick](#): > > Loaning a scanner probably isn’t auto repair but when the customer asks how do I fix a P0302? The answer is squarely in the auto repair category. > Picture this. Code p0302 misfire > Cust: how do I fix this? > AZ: spark plugs, wires, cap, and rotor should do it > Cust: take my money > Car still has a misfire. Cust is pissed and goes to BAR > BAR to shop that will be $5,000 please and if you do this again you will go to jail. Plus further complicating things, even if the parts guys keep their mouths shut some of the scanners themselves suggest fixes. But the big mystery of the other tread wasn’t the rationale for not reading codes in California, it was that the stores were able to read codes for years with no apparent problems until all of them stopped doing it around the same time. I assume there was some sort of court loss (like the scenario you describe above) or internal decision to crack down at the BAR, but whatever it was it isn’t findable via google. ---
**Author:** ![Yarster](https://avatars.discourse-cdn.com/v4/letter/y/7c8e57/32.png) [@Yarster](https://boards.straightdope.com/u/Yarster)\ **Post date:** [September 2, 2014, 10:18pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/23 "2014-09-02T22:18:53Z")
I’m in San Diego, CA and when my ‘check engine’ light went on and I went to AutoZone, they told me a change in the law now does not allow them to scan the cars for free any longer, which seems like a total scam to me. I took it to O’Reilly (the old Kragen) and they told me the same thing. They would SELL me a scanner, but not let me use theirs. I asked what happens if I ‘bought’ a scanner and then immediately returned it. Yeah, they told me they don’t take returns on scanners, go figure. Around here, all the places that do scans “for free” have an asterick next to it, which is “we won’t charge you for the scan if you let us do the repair to fix the problem and charge you for that”. At least that’s the story I heard here in town. End result? I bought a code scanner on Amazon and now all my friends hit me up when they have a problem and I keep it in my car for just that reason. It tells you what the code is, but you still need to look it up online, and then decide if it’s something you can do yourself. In my experience, the check engine light is most often either a loose gas cap, a bad O2 sensor, or a problem with the catalytic converter. The first two are pretty easy fixes. If it’s the catalytic converter, you are kind of fucked. It will involve welding and the replacement of expensive components to the tune of $800 (or at least that’s what it was for a 1996 Chevy Impala SS) ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [September 2, 2014, 10:20pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/24 "2014-09-02T22:20:31Z")
> [@cochrane](#): > > Your car’s check engine light shouldn’t be affected by your coolant or oil level. If it’s working properly it indicates a problem with your car’s emissions control system. . No. The “check engine” light indicates the computer has detected a need for a mechanic to check the engine. If it was quite low of oil then it might even get this ,as the low oil could allow excess knock (bearings for the crank shaft need oil pressure to float and centre properly.) BUT there are many errors - such as failing knock sensor, thermometers, pressure gauges, O2 and other gas senses… many many causes that can exist while the engine runs OK. (Perhaps uses more fuel.) Depend on the car, the code may just be a reminder to do a major service (there’s perhaps some parts eg Cam timing belt, accessories belt, water pump, oil pump that may need to be checked or replaced every , for example, 100,000 .) depending on the engine version in each model of car… ---
**Author:** ![slash2k](https://avatars.discourse-cdn.com/v4/letter/s/439d5e/32.png) [@slash2k](https://boards.straightdope.com/u/slash2k)\ **Post date:** [September 2, 2014, 10:26pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/25 "2014-09-02T22:26:44Z")
> [@kaylasdad99](#): > > What does OBD mean? OBD = On Board Diagnostics There’s a series of standards, for which OBD-II (generally mandated beginning in 1996 model year in the U.S.) is the most widespread. OBD-I was a predecessor, but it wasn’t really a standard, in that each manufacturer had their own code definitions and connection protocol. It may be possible to “read” the code for an OBD-I vehicle without a scanner, usually by shorting certain pins on the connector to generate a series of blinks. Count the blinks and look up what that number means for that manufacturer. ---
**Author:** ![robert\_columbia](https://avatars.discourse-cdn.com/v4/letter/r/e79b87/32.png) [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)\ **Post date:** [September 2, 2014, 11:47pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/26 "2014-09-02T23:47:33Z")
> [@Rick](#): > > Loaning a scanner probably isn’t auto repair but when the customer asks how do I fix a P0302? The answer is squarely in the auto repair category. > Picture this. Code p0302 misfire > Cust: how do I fix this? > AZ: spark plugs, wires, cap, and rotor should do it > Cust: take my money > Car still has a misfire. Cust is pissed and goes to BAR > BAR to shop that will be $5,000 please and if you do this again you will go to jail. What is “BAR”? Bureau of Auto Repair? And since when is auto repair such a regulated industry that someone can _go to jail_ for fixing (or trying to fix) a car? Or is this just garden-variety fraud in the sense that the “mechanic” sold a solution that they knew wouldn’t work? Do you actually need a license from the government to fix cars where you live? ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [September 3, 2014, 12:14am UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/27 "2014-09-03T00:14:25Z")
[quote=“robert\_columbia, post:26, topic:697183”] And since when is auto repair such a regulated industry that someone can _go to jail_ for fixing (or trying to fix) a car? /QUOTE] You can go to jail for disobeying a government body… Of course its an extreme for BAR to say to somebody “Don’t do X”… but disobeying (doing X ) can be a crime even if it was unreasonable to make the order. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 3, 2014, 2:06am UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/28 "2014-09-03T02:06:10Z")
> [@brad\_d](#): > > I think we’re on the same page here - that scenario is depressingly easy for me to envision. > > When my CEL comes on, I don’t ask the parts store guy how to address the code. Like all enlightened individuals, I get my free advice from the internet. 🙂 (And, in truth, message boards have helped me fix CEL-related issues before.) When I ran a parts house back in the pre-net days, I got asked a lot how to fix cars. That is one reason I went back to wrenching, I had professional shops calling and asking me how to fix shit. 🙂 > [@Yarster](#): > > Around here, all the places that do scans “for free” have an asterick next to it, which is “we won’t charge you for the scan if you let us do the repair to fix the problem and charge you for that”. This would be absolutely against the law in California. An ARD (Auto Repair Dealer) has to give an estimate in writing with a copy to the consumer before they work on the car. It is against the law to give a zero estimate, tell the customer it will be X t fix the car and then if they say no, tell them they owe Y dollars for the diagnostic. You can tell them it’s $X for the diagnosis, and if you choose to repair the car here, the fee will be waived. What most like these free diagnosis shop are doing is reading the code and telling the consumer You have code PXXXX, that indicates a problem with part X. I’m not sure if it is a bad part or something else, if you want me to go deeper, it will cost $XXX > [@](#): > > In my experience, the check engine light is most often either a loose gas cap, a bad O2 sensor, or a problem with the catalytic converter. The first two are pretty easy fixes. If it’s the catalytic converter, you are kind of fucked. It will involve welding and the replacement of expensive components to the tune of $800 (or at least that’s what it was for a 1996 Chevy Impala SS) :::Sigh::: No. first off the car we are talking about is OBD I. It doesn’t check the gas cap. Secondly go back and read posts 8 and 10. Your experience isn’t very wide spread. > [@Isilder](#): > > No. The “check engine” light indicates the computer has detected a need for a mechanic to check the engine. So much wrong in one post. No, it means the engine has detected something that will cause a rise in emissions. > [@](#): > > If it was quite low of oil then it might even get this ,as the low oil could allow excess knock (bearings for the crank shaft need oil pressure to float and centre properly.) in a word NO. Engine knock will not trip a CEL. But thanks for playing. > [@](#): > > BUT there are many errors - such as failing knock sensor, thermometers, pressure gauges, O2 and other gas senses… many many causes that can exist while the engine runs OK. > (Perhaps uses more fuel.) An open circuit at the knock sensor would be detected, a failing knock sensor? No. Thermometers? WTF? Cars don’t have thermometers. Temp sensors, yes, thermometers no. Pressure gauges if equipped are on the dash and not part of the OBD system. O2 and other gas senses… I gues you mean the O2 sensor, yes that is detected to different degrees between OBDI and II. What other gas sensors are you referring to? > [@](#): > > Depend on the car, the code may just be a reminder to do a major service (there’s perhaps some parts eg Cam timing belt, accessories belt, water pump, oil pump that may need to be checked or replaced every , for example, 100,000 .) depending on the engine version in each model of car… No, NO, NO! a check engine light is actually named a Malfunction Indicator Light. It is **NOT** a maintenance reminder light. > [@robert\_columbia](#): > > What is “BAR”? Bureau of Auto Repair? > > And since when is auto repair such a regulated industry that someone can _go to jail_ for fixing (or trying to fix) a car? Or is this just garden-variety fraud in the sense that the “mechanic” sold a solution that they knew wouldn’t work? Do you actually need a license from the government to fix cars where you live? BAR = Bureau of Automotive Repair. If you are running an unlicensed repair shop you can be fined. If they find you doing it more than once, yes the judge might send you to jail. Also if they find you suggesting unneeded repairs and they catch you with an uncover car, that is fraud and you can also go to jail for that. It is very common for people to complain about being ripped off getting their car fixed. California is trying to do things about that. California’s auto repair laws are strict, but if I follow the rules, my ass is bullet proof against complaints about how I run my business. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 3, 2014, 2:21am UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/29 "2014-09-03T02:21:53Z")
[quote=“Isilder, post:27, topic:697183”] > [@robert\_columbia](#): > > And since when is auto repair such a regulated industry that someone can _go to jail_ for fixing (or trying to fix) a car? /QUOTE] > > You can go to jail for disobeying a government body… > Of course its an extreme for BAR to say to somebody “Don’t do X”… > but disobeying (doing X ) can be a crime even if it was unreasonable to make the order. It is very common for the BAR to say don’t do that. [Here](http://www.bar.ca.gov/enforcement/DiscActions_Citations/May%202014%20Disciplinary%20Actions%20and%20Final%20Citations%20061314.pdf) is a list of don’t do its from May of this year. Scroll down for the dollar amounts of the fines. These boys are serious. ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [September 3, 2014, 7:42am UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/30 "2014-09-03T07:42:45Z")
$60 will buy a reader - a 92 probably has first gen software - two blinking led’s, IIRC. In which case the scanner is not needed - just a table of what the blinks are telling you. First find out what kind of OBD (?) you have, then find the interface - either a trapezoid plug or LED’s - then go from there. In CA Autozone is no longer allowed to perform the diagnostic - they got a nastygram from the State - it seems the garages charging $80 for the service didn’t like the competition. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [September 3, 2014, 3:30pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/31 "2014-09-03T15:30:25Z")
> [@usedtobe](#): > > …it seems the garages charging $80 for the service didn’t like the competition. Quite true, because in this case the competition wasn’t playing by the same rules. Parts stores didn’t have to deal with the fees, copious regulations, and strict (some would say extreme) standards of operation that licensed auto repair facilities were subject to. When faced with complying with those requirements, the parts stores realized that they couldn’t afford to do the service for free. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 3, 2014, 3:51pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/32 "2014-09-03T15:51:47Z")
Furthermore it is entirely legal for a licensed auto repair dealer to give away free diagnostics as long as they comply with the rules set down by the BAR. ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [September 3, 2014, 7:03pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/33 "2014-09-03T19:03:54Z")
Hey, did we ever find out what is wrong with the OPs rig? ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [September 3, 2014, 7:35pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/34 "2014-09-03T19:35:41Z")
> [@48Willys](#): > > Hey, did we ever find out what is wrong with the OPs rig? I’m taking the car to the mechanic tomorrow to find out. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 3, 2014, 7:45pm UTC](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183/35 "2014-09-03T19:45:51Z")
Keep us posted. [Previous page](https://boards.straightdope.com/t/my-cars-check-engine-light-has-the-sensor-gone-haywire/697183.md?page=1)