# Blinking Check engine light **URL:** \ **Category:** Factual Questions\ **Created:** [June 4, 2012, 12:39pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022 "2012-06-04T12:39:37Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [June 4, 2012, 12:39pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/1 "2012-06-04T12:39:37Z")
The check engine light on my 2002 Pontiac Vibe with 231K miles has started blinking. The car also idles slightly roughly, and my MPG has plummeted. Checking out on line, it seems this indicates an emissions failure that could compromise the Cat Converter. However, many articles say this is big problems, stop driving, and get the car towed in. From what I have read, this is ludicrous. Now the shop (Firestone) wants to charge me $100 just to read the codes and diagnose the problem. This also sounds ludicrous. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [June 4, 2012, 1:03pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/2 "2012-06-04T13:03:18Z")
Check with the local auto parts stores - many of them will read codes as a free service (obviously with the hopes that you’ll buy whater’s needed from them). Otherwise, you can buy your own code reader - they start out at about $20. ---
**Author:** ![Mithras](https://avatars.discourse-cdn.com/v4/letter/m/f04885/32.png) [@Mithras](https://boards.straightdope.com/u/Mithras)\ **Post date:** [June 4, 2012, 1:13pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/3 "2012-06-04T13:13:33Z")
If I’m remembering right, my (now departed) Grand Prix had that happen. The issue was something like a piston misfiring and the computer therefore put the car into limp mode. It didn’t take a huge outlay to get it fixed by my local mechanic. So there’s at least a chance that it won’t end up costing you an arm and a leg. But why would it be ludicrous that when your car is telling you something is wrong with the engine, you should drive it as little as possible and get it checked out right away? ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [June 4, 2012, 1:30pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/4 "2012-06-04T13:30:43Z")
A blinking CEL indicates a severe misfire which can damage / destroy the converter in very short order. Should you drive it? I don’t know, how lucky do you feel? You may be able to baby it to the shop and there will be no damage, you might destroy it on the way to the shop, or it might already be dead. Depends on how long you have been driving it and how severe the miss is. As far as the diagnostic fee at Firestone goes when you go to the doctor does he charge you for an office visit and labs tests? If you don’t have a problem with that why do you have a problem with a shop doing the same for your car? All a shop has to sell is parts and labor. Diagnosing a car takes up shop time (labor). That time needs to generate income or the shop could go belly up. While I know you probably don’t care if the shop goes out of business, but the shop owners and employees do care. Therefore there is a diagnostic charge. $100 is probably 1 hour of technician’s time which should be sufficient to find the root cause of a misfire. ---
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [June 4, 2012, 1:52pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/5 "2012-06-04T13:52:45Z")
Two things. First, I do not care if the cat converter dies. I only care about damaging the engine or car itself. It is just under two years until I need it inspected again. Second, it seems that they read the codes and call me, that there should be no time involved. In fact, my sense is that they are charging me for somethings that makes their job easier. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 4, 2012, 1:58pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/6 "2012-06-04T13:58:10Z")
> [@dauerbach](#): > > The check engine light on my 2002 Pontiac Vibe with 231K miles has started blinking. The car also idles slightly roughly, and my MPG has plummeted. Checking out on line, it seems this indicates an emissions failure that could compromise the Cat Converter. However, many articles say this is big problems, stop driving, and get the car towed in. From what I have read, this is ludicrous. Now the shop (Firestone) wants to charge me $100 just to read the codes and diagnose the problem. This also sounds ludicrous. Auto parts stores typically will lend you, free of charge, a diagnostic code reader so you can read the actual code. Often, this is enough information for you to solve the problem, but sometimes the problem isn’t what you think it is. Example: suppose you go to the auto parts store, borrow their reader, and the code that comes up says that the signal from an O2 sensor is off-scale low. You buy a new sensor, install it, and 99 times out of 100, the problem is cured. That one time out of 100 though, the sensor is fine, and something is wrong with the wiring between it and the ECU. You replace the sensor for $100, and the problem persists. If you go to a car repair place (e.g. Firestone, or your dealer) and ask them to ID the problem, they’ll charge you $100 (this is enough to cover ~1 hour of labor), and they will pin down _exactly_ what the problem is so you don’t waste time and money replacing/repairing the wrong thing. Nothing ludicrous about it. In the case of a persistent misfire, is the problem the spark plug, the plug wire, the coil, or the ECU? Or maybe the fuel injector is squirting in way too much (or way too little) fuel? Your $100 is paying them to figure this out. And yes, if your engine is dumping unburned fuel-air mixture into the exhaust system, you can wreck the catalytic converter in fairly short order. This is not ludicrous either. ---
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [June 4, 2012, 2:00pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/7 "2012-06-04T14:00:09Z")
Just heard from Firestone, about an hour after I dropped it off. I don’t think they took much time to figure things out. They said one ignition coil was dead, another on the way out, that I needed a new battery cable, my throttle body needed to be cleaned, and I needed four new plugs. I always thought you could just clean off fouled plugs with gasoline. However, since the plugs have never been changed I told them ok. I will do the cable myself, and I imagine the throttle body cleaning will either happen by itself, or I can spend 10 bucks and do it myself. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [June 4, 2012, 2:14pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/8 "2012-06-04T14:14:05Z")
If you could clean them with gasoline then they would never get dirty. More likely they are worn out. Spark plugs do wear and need to be changed on a regular basis generally every 60-100K miles depending on the engine. When the plug goes out it can take out the coil in short order. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 4, 2012, 2:15pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/9 "2012-06-04T14:15:22Z")
> [@dauerbach](#): > > Just heard from Firestone, about an hour after I dropped it off. I don’t think they took much time to figure things out. They said one ignition coil was dead, another on the way out, that I needed a new battery cable, my throttle body needed to be cleaned, and I needed four new plugs. I always thought you could just clean off fouled plugs with gasoline. However, since the plugs have never been changed I told them ok. I will do the cable myself, and I imagine the throttle body cleaning will either happen by itself, or I can spend 10 bucks and do it myself. Plugs last a long time, but not forever. The spark is extremely high temperature, and over time it erodes the electrodes away. Spark plugs with the correct heat rating rarely become fouled now that leaded gasoline is no longer in use. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 4, 2012, 2:19pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/10 "2012-06-04T14:19:32Z")
> [@dauerbach](#): > > Just heard from Firestone, about an hour after I dropped it off. I don’t think they took much time to figure things out. They said one ignition coil was dead, another on the way out, that I needed a new battery cable, my throttle body needed to be cleaned, and I needed four new plugs. I always thought you could just clean off fouled plugs with gasoline. However, since the plugs have never been changed I told them ok. I will do the cable myself, and I imagine the throttle body cleaning will either happen by itself, or I can spend 10 bucks and do it myself. you’ve never changed the spark plugs in 231,000 miles? it’s not only a matter of fouling, it’s that over time the electrodes erode away due to the repeated arcing and the spark gap tends to grow wider. Thus, ignition reliability suffers. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 4, 2012, 2:23pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/11 "2012-06-04T14:23:03Z")
> [@dauerbach](#): > > Two things. First, I do not care if the cat converter dies. I only care about damaging the engine or car itself. It is just under two years until I need it inspected again. Catalysts can be several hundred dollars to replace if they are damaged, and you won’t pass inspection with a non-functioning or non-present catalyst. And yes, continuing to drive with a repetitive misfire can overheat the catalyst and risk damaging the car (in other words, fire.) > [@](#): > > Second, it seems that they read the codes and call me, that there should be no time involved. In fact, my sense is that they are charging me for somethings that makes their job easier. Do you work for free? Why do you expect others to do so? Time they waste pulling codes for you is time they aren’t working on a paying job. ---
**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\ **Post date:** [June 4, 2012, 2:45pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/12 "2012-06-04T14:45:01Z")
> [@dauerbach](#): > > Two things. First, I do not care if the cat converter dies. I only care about damaging the engine or car itself. It is just under two years until I need it inspected again. Second, it seems that they read the codes and call me, that there should be no time involved. In fact, my sense is that they are charging me for somethings that makes their job easier. A damaged converter _can_ cause excessive back pressure in the engine, significantly decrease the engine’s power output, and increase your fuel consumption considerably. That adds up to a vehicle that is potentially unsafe and environmentally unfriendly. ---
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [June 4, 2012, 3:14pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/13 "2012-06-04T15:14:36Z")
So, I can see why things need to be taken care of expeditiously, but the stop and have it towed suggestions elsewhere in the web seem to have been over the top. When I have had “routine maintenance” performed in the past I have had serious problems, including the time the dealer adjusted the valves and did not torque down the valve cover. My wife called me at work to say there was an ocean of oil under the car. Because of this, I now only fix what is broken. Like I said, I did ok having the plugs replaced, I thought it might be time. And perhaps I did cause my own problem by letting the plugs age excessively. I still remember when mechanics used to diagnose things as a part of the repair. When I get my brakes done they do not charge extra for removing the tire. This seems the same to me. Also, is there a code for ignition coil failure? If so, then the diagnosis did only take 30 seconds, and I am being charged an exorbitant amount. If not, then perhaps they did take SOME little time to diagnose it. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 4, 2012, 3:25pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/14 "2012-06-04T15:25:08Z")
> [@dauerbach](#): > > So, I can see why things need to be taken care of expeditiously, but the stop and have it towed suggestions elsewhere in the web seem to have been over the top. hardly. Depending on how bad the misfire condition is, the catalyst can be damaged very quickly. You need to understand what the catalyst is doing. Part of its function is cleaning up carbon monoxide and hydrocarbons (e.g. unburnt fuel.) it does this by oxidizing these pollutants into CO2 and H20. An oxidation reaction generally produces heat. The catalyst is designed to work within the temperature range of a properly functioning engine. When you have a repeated misfire, you’re dumping far more unburned fuel into the exhaust and the excessive heat of burning it up in the catalyst can destroy it in short order. > [@](#): > > Because of this, I now only fix what is broken. Like I said, I did ok having the plugs replaced, I thought it might be time. And perhaps I did cause my own problem by letting the plugs age excessively. ya think? > [@](#): > > I still remember when mechanics used to diagnose things as a part of the repair. When I get my brakes done they do not charge extra for removing the tire. This seems the same to me. Also, is there a code for ignition coil failure? there are, but the PCM has to be able to sense a problem with the circuit (open or shorted.) If you only get “Misfire Cylinder #_x_” and the tech then has to figure out what’s causing the misfire. compression loss, spark plug, coil/wire, fuel injector, etc. > [@](#): > > If so, then the diagnosis did only take 30 seconds, and I am being charged an exorbitant amount. If not, then perhaps they did take SOME little time to diagnose it. you seem to lack the knowledge necessary to come to that sort of conclusion. ---
**Author:** ![bucketybuck](https://avatars.discourse-cdn.com/v4/letter/b/898d66/32.png) [@bucketybuck](https://boards.straightdope.com/u/bucketybuck)\ **Post date:** [June 4, 2012, 3:28pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/15 "2012-06-04T15:28:26Z")
> [@dauerbach](#): > > If so, then the diagnosis did only take 30 seconds, and I am being charged an exorbitant amount. If not, then perhaps they did take SOME little time to diagnose it. At the end of the day, YOU do not have the ability nor the knowledge to diagnose your own problems. So, frankly, its not your place to decide what is a fair price for doing so. > [@](#): > > **The parable of the repair man** > One day in a large factory with a long assembly line a critical machine suddenly stopped working. This brought the entire assembly line to a halt and partially finished products were backed up all through the factory. The company that owned the factory was in a panic as they were losing thousands of dollars for every hour that the factory was shut down. > > The chief mechanic was called in and he insisted that there was only one expert who he knew could correct the problem quickly so the expert was called in. When the expert arrived, he was a modest looking man in common work clothes carrying a small toolbox. He examined the halted machine for about ten minutes then removed a hammer from his toolbox. He struck the machine once with the hammer and suddenly the machine started running at full capacity. Goods started moving smoothly down the assembly line at full rate and the factory was back online. > > The expert then presented the chief mechanic with a bill for $5000. “This is outrageous!” the mechanic exclaimed “5000 dollars to hit a machine with a hammer?” The expert replied “Oh, let me itemize that bill for you.” and presented the chief mechanic with the following itemized invoice: > > Hitting machine with hammer ….…………$5.00 > Knowing where to hit machine ….…$4995.00 ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [June 4, 2012, 3:31pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/16 "2012-06-04T15:31:49Z")
The one hour charge for plugging in the meter and reading the code is borderline unethical IMHO -though perhaps they don’t want to be in the business of car code readers so overprice it to discourage it. If all you want done us the code read then take it to a auto parts store, call first to see if they do it for free - many do. If possible don’t heat up your car that much - take a direct route to the closest one that will do it, or buy/borrow a code reader taking another car. This, along with the internet, will give you some concept of what’s wrong and may allow you to fix it yourself. Then if it’s beyond you you can put the shop’s expertise to work. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 4, 2012, 3:37pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/17 "2012-06-04T15:37:39Z")
> [@kanicbird](#): > > The one hour charge for plugging in the meter and reading the code is borderline unethical IMHO -though perhaps they don’t want to be in the business of car code readers so overprice it to discourage it. “Unethical?” How is it so if the charge is disclosed up front? and yes, I can believe it’s done to discourage people who want to come in, waste your time pulling codes for them so they can pop off and try to fix the problem themselves. If I’m in the business of _fixing_ cars, I need to be doing that. Auto parts stores will do it for free because they want to sell you parts. Even better for them if you shotgun 12 parts onto a car to try to fix a wiring problem 😃 ---
**Author:** ![bucketybuck](https://avatars.discourse-cdn.com/v4/letter/b/898d66/32.png) [@bucketybuck](https://boards.straightdope.com/u/bucketybuck)\ **Post date:** [June 4, 2012, 3:43pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/18 "2012-06-04T15:43:05Z")
> [@kanicbird](#): > > The one hour charge for plugging in the meter and reading the code is borderline unethical IMHO I don’t know about auto-parts stores in the US, but in the dealership I currently work for you can be looking at about €14000 for the full diagnostic kit and it is mandatory to have it to remain a main dealer. I know there are cheapy cheap code readers floating about that give you a code and fuck all else, but if you want a proper diagnostic done, with injector tests or pressure tests etc etc, then you need the dealer, and they need to reclaim their costs. Nothing unethical about that whatsoever. Thats the other problem though. Many people still think we have magic diagnostic computers that tell you within five minutes whats wrong and how to fix it. Sometimes yes, but very often this is not the case. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [June 4, 2012, 3:43pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/19 "2012-06-04T15:43:23Z")
> [@jz78817](#): > > “Unethical?” How is it so if the charge is disclosed up front? Charging for a hour of your time for something that is known to take 5-15 minutes, including talking to the customer and ringing them up and you ask how? That time can be easily doubled billed to others. It is generally considered unethical for charging the for the same time more then once - and a 15 minute job on the outside, allows that same hour to be charged four times (assuming 4 customers requesting this in the hour). So it is unethical from the point of billing the same time to multiple customers. Also it’s not like the shop comes to you and has to pay for travel. But if it’s a way to discourage them being used that way it makes sense. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [June 4, 2012, 3:44pm UTC](https://boards.straightdope.com/t/blinking-check-engine-light/624022/20 "2012-06-04T15:44:23Z")
The guy has to make enough money to pay his rent and his workers. Giving away free diagnosis is not necessarily going to do that, unless you give it away to someone who is a solid regular customer. So, he tells you the diagnosis is free, and you find out it’s a set of bad spark plugs/wires and distributor cap/rotor. Anyone who knows which side of the ratchet to hold can change those, so you tell the guy you’re not paying him $50/hr to do simple maintenance, and take the car home to do it yourself. He’s out the time to do the diagnosis, and potentially time he scheduled for your car’s repairs, and gets squat in return. I’ve been going to my mechanic for 5 years, oil changes, brakes, alternator, etc. He’s let me off the hook on payments for diagnosing DIYish problems and for inspecting prospective cars to buy, because he knows I will be back the next time I need service. [Next page](https://boards.straightdope.com/t/blinking-check-engine-light/624022.md?page=2)