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remember that the computer codes you pull up tell you want system is being affected, not what is actually wrong. you might have a vacuum leak, a drop in cylinder pressure, a bad fuel injector, a problem in the electrical system that is affecting the particular cylinder. its possible that the wiring has been compromised somehow, perhaps a bad connection, damaged wiring, etc. check with the dealer in your area for any TSBs related to this issue.
Does your car have to past a yearly emissions test? If not DONT WORRY ABOUT THE CEL LIGHT BEING OWN. You need to understand a little more about the OBD11 system on your car and you will know why I said that.
Horrendous advice.
P0304 is a misfire. Which could then lead to a P0420 because of the raw fuel being dumped into the cat.
While there are codes you can.. Pretty safely ignore.. This isn't one of them.
There's a reason that cylinder is misfiring. As.. Someone above said.. The shop you're at is loading up the parts cannon and firing. And they've missed.
Don't return to them. Yeah.. you've already given them money, but.. No sense in throwing good after bad.
Seeing as they replaced 4 plugs, that at least tells me that you have a 4 cylinder. So, starting point. We basically know it's not the plug or the coil at this point.
What you need.. Fuel, Spark, Air.. And all at the right time and in the right amounts with the right amount of pressure applied..
Spark.. You've.. Covered, I think. plug and Coil are new..
Fuel.. You COULD be looking at an injector/injector pulse problem. Either the injector is clogged/not working, or perhaps it's not getting the signal intermittently. I do seem to recall some Toyotas having issues with injectors, but.. I honestly cannot tell you the years. This is plausible because it's affecting a single cylinder.
Air.. Oh, so many things. Someone mentioned intake. Possible, but I'd lean away due to the fact that this is happening on a single cylinder. If the intake were the problem, I'd expect to see a P0300 alongside. Not saying they're wrong, just.. Not high on my suspect list. You'd also likely have other codes, such as a P0171.. Or Would that be a P0175.. 171 is lean, 175 is rich. If there's extra air getting in.. Should be a 171.. Which then means the PCM would dump extra fuel in and the trims would show rich? I have to look this up every time.. Anyway.. Your trims would be out of whack, and likely another code would be set.
A head gasket.. This is possible. Toyota isn't known for those.. But a break.. I'd really expect that to throw codes on 2 cylinders. head gaskets, my experience.. Usually break between cylinders.. Or from the water jacket to the outside of the engine.. From cylinder to outside.. I don't do much, but I've never seen it myself. Now, it could also be the head itself.. But.. I put this with the intake. I think it's a low probability.
Compression loss on the cylinder.. This would be quite odd.. But.. You don't mention the miles on the engine. So, this is more possible than the above two.. However.. If this engine is under 200k, being a toyota.. I'd be surprised. Hell, being a toyota, I'd be surprised if it was happening under 300k. Compression and Leakdown test would confirm/exclude this. This would, however, generally only throw the single code.
Valve issues.. a valve not closing fully.. Honestly.. This is where my mind goes at the moment. Don't rely on that, obviously and don't let me freak you out. I haven't seen your car, just have your words to go off of. However, a valve not operating fully.. That could do it. And it could even be a worn cam causing the valve not to work properly.
Jumped timing.. I don't see this. Not a single cylinder issue.
I guess we should throw "Bad PCM" in here.. But, if that were the case, and yes, you can have a dead cylinder due to a bad PCM.. It would be dead. You wouldn't be complaining about a CEL. You'd be complaining that you were running on 3 cylinders, and it would have never left the shop with the problem still existing.
Anyway.. That's just my rambling thoughts on it. I would like to know the mileage we're looking at.. Being an '02.. I mean, I am not going to be surprised to hear anything from 50k to 300k.
Does your car have to past a yearly emissions test? If not DONT WORRY ABOUT THE CEL LIGHT BEING OWN. You need to understand a little more about the OBD11 system on your car and you will know why I said that.
My Jeep was popping a CEL every day. I kept getting the codes checked and cleared (no, it was not the fuel cap), and finally got my own code reader. I don't remember what the code was, but it was always something to do with emission controls, something to do with the fuel tank.
So, while it was in for a clutch change, I had the tank checked. AHAH!! Broken fitting on the evap system. No parts available (the Jeep is 15 years old). It runs fine, I have no emissions inspection to worry about, so the CEL is on all the time now. I may cover it with tape.
YES, you need to find out exactly why the CEL is coming on. When you find out what the problem is, then you can make an informed decision what to do about it, if anything.
Good luck.
I used to have a Saturn SL1 that misfired (I do not remember if there was a code associated with the check engine light). Anyway, the mechanic said I needed new coils. I had it done. Same problem occurred. For some reason, I thought it might be a little water in the gas tanks. I treated a couple of tanks with an STP gas additive to remove water. Problem solved.
I have a 2002 Toyota Highlander. A few weeks ago the Check Engine Light came on (I never ignore it) and I had it checked, it was code PO 304, cyl 4 misfire. I wound up getting one new ignition coil and 4 spark plugs (also got oil/filter change) for $500 total repair. (Car does not have 110K miles yet, have owned it 11 years.)
The next week the CEL came on again -- took it in to read code -- the same one. I left car for day and they checked it all out again, other coils ok, mechanic drove it around half-hour- CEL did not come on again.
About another week/50 miles later, CEL comes on again Christmas Eve. Took it back yesterday just to read code -- same one. They asked me to bring it back Monday and leave it again. I asked if they can't at least delete the repeating code ...they said they have some $5,000 machine that has to run for an hour that checks everything, whatever that is. I am tired of worrying about the CEL light...as mentioned, I don't like to ignore. I am aware it could be "gas cap loose" (happened several times) or something far more serious. This could wind up being one of the other coils. My worst nightmare is just having my car die on me in traffic, as it did several years back when the alternator went.
I am wondering if these guys know what they're doing or I should get a second opinion somewhere else and at least see if they get the same code?? I've been going to this shop for years (essentially 3-store tire chain with repair shop...but personnel change a lot) and I like to think they are straight with me and don't upsell when I don't need something... I just am having the sense they really don't know what's wrong.
Any thoughts? Thanks!
You can just "delete the repeating code." Why not? With the problem not fixed the code will come back. This has nothing to do with the gas cap. It is a #4 cylinder misfire. The great bulk of these are ignition coil or spark plug problems but not 100%. One possible cause is head gasket seepage causing water to get into the offending #4 cylinder overnight and cause a misfire on startup. The shop needs to park the car with the cooling system pressurized for several hours or overnight and observe carefully what happens on startup. A big cloud of steam out the tailpipe would be indicative of head gasket problems as also a misfire that goes away after a few seconds.
Has there been any mysterious loss of engine coolant? Has the coolant level even been checked?
If the Highlander keeps throwing the P0304 code for #4 cylinder misfire do not worry about the other coils.
Well-intended that they gave your SUV a half-hour test drive but this will almost certainly not find a head gasket seepage problem.
FYI, while there are exceptions, a tire chain store is not the place to take a car to diagnose an intermittent and somewhat elusive problem.
These are thoughts from the co-owner of a repair shop for forty years and one that sees a LOT of Toyotas.
"Fixing P0304 should be considered a high priority. Unlike a lot of the OBDII codes, this code has to do directly with engine combustion. It also can cost money to ignore it, since driving with a misfire can damage the vehicle’s catalytic converter. The engine is also not firing all of the fuel, so raw fuel is also passing through Cylinder 4 into the exhaust. Mileage may suffer as well when your Highlander has P0304 as well."
Take to the Toyota dealer. Ask to diagnose and estimate. Do not authorize any repairs until you find out what is the issue. Do not drop off and leave. Be a "wait" customer.
While you wait may not work for a problem such as overnight head gasket seepage.
P0304 is a misfire. Which could then lead to a P0420 because of the raw fuel being dumped into the cat.
While there are codes you can.. Pretty safely ignore.. This isn't one of them.
There's a reason that cylinder is misfiring. As.. Someone above said.. The shop you're at is loading up the parts cannon and firing. And they've missed.
Don't return to them. Yeah.. you've already given them money, but.. No sense in throwing good after bad.
Seeing as they replaced 4 plugs, that at least tells me that you have a 4 cylinder. So, starting point. We basically know it's not the plug or the coil at this point.
What you need.. Fuel, Spark, Air.. And all at the right time and in the right amounts with the right amount of pressure applied..
Spark.. You've.. Covered, I think. plug and Coil are new..
Fuel.. You COULD be looking at an injector/injector pulse problem. Either the injector is clogged/not working, or perhaps it's not getting the signal intermittently. I do seem to recall some Toyotas having issues with injectors, but.. I honestly cannot tell you the years. This is plausible because it's affecting a single cylinder.
Air.. Oh, so many things. Someone mentioned intake. Possible, but I'd lean away due to the fact that this is happening on a single cylinder. If the intake were the problem, I'd expect to see a P0300 alongside. Not saying they're wrong, just.. Not high on my suspect list. You'd also likely have other codes, such as a P0171.. Or Would that be a P0175.. 171 is lean, 175 is rich. If there's extra air getting in.. Should be a 171.. Which then means the PCM would dump extra fuel in and the trims would show rich? I have to look this up every time.. Anyway.. Your trims would be out of whack, and likely another code would be set.
A head gasket.. This is possible. Toyota isn't known for those.. But a break.. I'd really expect that to throw codes on 2 cylinders. head gaskets, my experience.. Usually break between cylinders.. Or from the water jacket to the outside of the engine.. From cylinder to outside.. I don't do much, but I've never seen it myself.
Seepage from water jacket into #4 cylinder only. Not far fetched at all. We see this kind of problem from time to time at my shop.
Quote:
Originally Posted by Labonte18
Now, it could also be the head itself.. But.. I put this with the intake. I think it's a low probability.
Compression loss on the cylinder.. This would be quite odd.. But.. You don't mention the miles on the engine. So, this is more possible than the above two.. However.. If this engine is under 200k, being a toyota.. I'd be surprised. Hell, being a toyota, I'd be surprised if it was happening under 300k. Compression and Leakdown test would confirm/exclude this. This would, however, generally only throw the single code.
Valve issues.. a valve not closing fully.. Honestly.. This is where my mind goes at the moment. Don't rely on that, obviously and don't let me freak you out. I haven't seen your car, just have your words to go off of. However, a valve not operating fully.. That could do it. And it could even be a worn cam causing the valve not to work properly.
Jumped timing.. I don't see this. Not a single cylinder issue.
I guess we should throw "Bad PCM" in here.. But, if that were the case, and yes, you can have a dead cylinder due to a bad PCM.. It would be dead. You wouldn't be complaining about a CEL. You'd be complaining that you were running on 3 cylinders, and it would have never left the shop with the problem still existing.
Anyway.. That's just my rambling thoughts on it. I would like to know the mileage we're looking at.. Being an '02.. I mean, I am not going to be surprised to hear anything from 50k to 300k.
Maybe it's as simple as a leaky fuel injector, allowing fuel to leak into the combustion chamber, after the engine is shut down, causing the code to set when the engine is re-fired. Cheapest attempt at a fix would be a container of good fuel system cleaner, like Techron or Red Line fuel system cleaner. Absolute worst case, that's not the problem, but at the same time, you've cleaned out your fuel system and wasted only a few minutes and a few dollars.
P0304 is a misfire. Which could then lead to a P0420 because of the raw fuel being dumped into the cat.
While there are codes you can.. Pretty safely ignore.. This isn't one of them.
There's a reason that cylinder is misfiring. As.. Someone above said.. The shop you're at is loading up the parts cannon and firing. And they've missed.
Don't return to them. Yeah.. you've already given them money, but.. No sense in throwing good after bad.
Seeing as they replaced 4 plugs, that at least tells me that you have a 4 cylinder. So, starting point. We basically know it's not the plug or the coil at this point.
What you need.. Fuel, Spark, Air.. And all at the right time and in the right amounts with the right amount of pressure applied..
Spark.. You've.. Covered, I think. plug and Coil are new..
Fuel.. You COULD be looking at an injector/injector pulse problem. Either the injector is clogged/not working, or perhaps it's not getting the signal intermittently. I do seem to recall some Toyotas having issues with injectors, but.. I honestly cannot tell you the years. This is plausible because it's affecting a single cylinder.
Air.. Oh, so many things. Someone mentioned intake. Possible, but I'd lean away due to the fact that this is happening on a single cylinder. If the intake were the problem, I'd expect to see a P0300 alongside. Not saying they're wrong, just.. Not high on my suspect list. You'd also likely have other codes, such as a P0171.. Or Would that be a P0175.. 171 is lean, 175 is rich. If there's extra air getting in.. Should be a 171.. Which then means the PCM would dump extra fuel in and the trims would show rich? I have to look this up every time.. Anyway.. Your trims would be out of whack, and likely another code would be set.
A head gasket.. This is possible. Toyota isn't known for those.. But a break.. I'd really expect that to throw codes on 2 cylinders. head gaskets, my experience.. Usually break between cylinders.. Or from the water jacket to the outside of the engine.. From cylinder to outside.. I don't do much, but I've never seen it myself. Now, it could also be the head itself.. But.. I put this with the intake. I think it's a low probability.
Compression loss on the cylinder.. This would be quite odd.. But.. You don't mention the miles on the engine. So, this is more possible than the above two.. However.. If this engine is under 200k, being a toyota.. I'd be surprised. Hell, being a toyota, I'd be surprised if it was happening under 300k. Compression and Leakdown test would confirm/exclude this. This would, however, generally only throw the single code.
Valve issues.. a valve not closing fully.. Honestly.. This is where my mind goes at the moment. Don't rely on that, obviously and don't let me freak you out. I haven't seen your car, just have your words to go off of. However, a valve not operating fully.. That could do it. And it could even be a worn cam causing the valve not to work properly.
Jumped timing.. I don't see this. Not a single cylinder issue.
I guess we should throw "Bad PCM" in here.. But, if that were the case, and yes, you can have a dead cylinder due to a bad PCM.. It would be dead. You wouldn't be complaining about a CEL. You'd be complaining that you were running on 3 cylinders, and it would have never left the shop with the problem still existing.
Anyway.. That's just my rambling thoughts on it. I would like to know the mileage we're looking at.. Being an '02.. I mean, I am not going to be surprised to hear anything from 50k to 300k.
I agree but knowing which codes are important and which ones dont affect the driveability of the car is important.Reading the codes and knowing what they mean as far as how to fix them often requires an experienced mechanic. good luck
Seepage from water jacket into #4 cylinder only. Not far fetched at all. We see this kind of problem from time to time at my shop.
Leakdown/Compression test ought to show this, then. Perhaps not obviously, but you'd see off readings and could then move on to something like sticking a scope in to see it looks like.
As I mentioned in another topic.. I am no fan of not fixing anything that causes a light.. Though I do understand the economics of things and that there are some things that you just can't find a part for.
In those cases.. I say get a code reader because the danger of leaving the light on and ignoring it.. It doesn't do anything different when there's ANOTHER code stored.
So.. The P0449, for example, that you're ignoring.. you never know when the P0128, P0171, P0300 also pop up.
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