On many occasions in The Big Bang Theory we have seen Penny being questioned about the "check engine" light, especially by Sheldon Cooper and even by Beverly Hofstadter. So is there any significance or just Penny's carelessness?

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    May be she is just careless and spends her salary in other things like makeup & dresses. I believe it only reason.
    – Panther
    Commented Sep 8, 2015 at 6:38
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    @panther you spelt Wine wrong.
    – cde
    Commented Sep 8, 2015 at 12:55
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    @cde or shoes. She buys a lot of shoes.
    – alroc
    Commented Sep 8, 2015 at 20:15
  • OT, but this question made me think of the following conversation from "Last Man Standing": Dad: "So Mandy, now you know that the 'check engine'-light doesn't just mean for you to check that you have an engine." Daughter: "I already knew I had an engine, it was where the smoke was comming from." (or something along those lines) Commented Sep 9, 2015 at 8:59

3 Answers 3


The check engine light is being used as an indicator of the relative difference in general concern by Penny versus Sheldon or Beverly.

The check engine light in modern vehicles quite often indicates an issue with the emissions control system, although as commenters have noted it can cover a wide variety of vehicle faults (including those unrelated to the engine). Often these underlying issues pose no immediate danger to the mechanical function of the car, the initial symptoms of emissions issues being increased environmentally-harmful emissions and lower fuel economy.

Thus, many people ignore the check engine light, either after checking it once and finding out that the underlying issue is emissions-related or otherwise not immediately harmful, or in some cases never checking it at all. However, there is always a chance that the problem is one that may quickly damage the vehicle, and the only way to know for sure is to have the error code checked by a mechanic (or checking it yourself if you have the specialized equipment). In addition, a person who cares deeply about their environmental impact would want to fix any underlying emissions problem, not to mention the potential for long term damage if the light is consistently ignored.

Thus, response to the check engine light can show how careful a person is along a continuum from most careless to most careful:

  • completely ignoring it from the get go
  • having it checked the first time it is lit but assuming things are fine on subsequent lights
  • having it checked it every time it goes on
  • not operating the vehicle until the underlying cause is solved

Sheldon and Beverly are both of the sort that is very concerned with minutiae, and Sheldon in particular has shown concern for potential issues of low probability but high potential impact. Both are detail-oriented and meticulous. Penny, conversely, lives a somewhat oblivious existence, relying on her ability to respond to situations rather than on extensive planning, care, or forethought. Their responses to the check engine light are indicative of these personality traits.

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    The check engine light, also known more correctly as the Malfunction Indicator Light actually covers far more than the engine and emissions systems in modern cars, such as the brakes (P0504), air conditioning (P0535), security system (P0513), steering (P0635) and transmission (P0700). See the OBDII standard for a complete list, and many manufacturers will add their own proprietary codes as well, especially on the high end brands. And besides checking it yourself, or sending it to a mechanic, some big box autoparts stores like AutoZone will check it for free and tell you what codes are stored.
    – Matt
    Commented Sep 9, 2015 at 1:06
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    @mattburnett Quite true. Someone appears to have deleted my previous comment re: coverage of the complete universe of technical details on the light, but the purpose in this answer is to cover it in regards to its use as a narrative device, rather than to provide content better suited for the Mechanics beta stack exchange. As noted in the answer it can be a variety of underlying causes.
    – phoebus
    Commented Sep 9, 2015 at 1:11
  • What's not mentioned is that the show is set in California, and Pasedena of Los Angeles county is subject to Smog Checks. So, not resolving a Check Engine indicator in Penny's case could lead her to fail a smog check and possibly lose the ability to legally drive her car (until it's resolved).
    – user23604
    Commented Sep 9, 2015 at 2:12
  • @CreationEdge My guess is that staying on top of smog checks may fall under the same level of care she has for the CEL ;)
    – phoebus
    Commented Sep 9, 2015 at 2:13
  • Yes, and also is more reason for someone like Sheldon to be on top of it, because it's not only good for maintenance but the law.
    – user23604
    Commented Sep 9, 2015 at 2:14

It is also implied, deliberately or otherwise, that she doesn't understand what the light is for. In Series 2 Episode 14 – The Financial Permeability, there is a conversation between Penny and Sheldon where the engine does inevitably break:

Sheldon: If you recall, I pointed out the “check engine” light to you several months ago.

Penny: Well the “check engine” light is fine. It’s still blinking away. It’s the stupid engine that stopped working. It cost me like twelve hundred dollars to fix it.

Quote Source

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    This reads to me like a simple joke, not an indicator that Penny didn't know what the light meant.
    – user15995
    Commented Sep 8, 2015 at 13:43
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    @Lilienthal, well, maybe, but if the light is on even after fixing the engine, then what does it indicate? Commented Sep 8, 2015 at 14:24
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    @Lilienthal I was looking for a video of the quote, because although it reads like a joke it's played very deadpan so doesn't sound like one (although obviously it is there for laughs) Commented Sep 8, 2015 at 14:45
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    @Lilienthal have you not met Penny?
    – cde
    Commented Sep 8, 2015 at 14:50
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    It is definitely deadpan, but I always assumed like you that it was a joke at the time and not implying she didn't know what it meant. Given Sheldon's (and Amy's and Beverly's) repeated comments about it, it strains credulity that she could not in a general sense know what it means. (It's also at odds with her Nebraska Corn Fed personality. She almost certainly would have had some knowledge of car repair.)
    – Joe
    Commented Sep 8, 2015 at 16:59

It should also be noted that Penny is a waitress and doesn't really make much, for regularly maintaining a costly possession like a car.

So, she doesn't care about the car's condition unless and until the problem is a major, like the one pointed out by @MatthewSteeples. In Penny's words:

Sheldon: If you recall, I pointed out the “check engine” light to you several months ago.

Penny: Well the “check engine” light is fine. It’s still blinking away. It’s the stupid engine that stopped working. It cost me like twelve hundred dollars to fix it.

So, a sensible inference to make is that even if she knows what the light is or, she can't/doesn't really care to repair it as she cannot afford minutiae servicing (which can cost a lot for a car).

In addition, Penny represents most (American) common people. And most people don't really care about the environment unless it is directly spoiling our health or is costing us a lot. Thus the reluctance of Penny towards servicing the problem.

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