QuestionQUESTION: Hello,
I just went to renew my plates the other day, and I was refused due to the lack of emmisions test. I went to get the car all checked out, but find out that it needs some repairs.
The codes given were P0304, and P0501. From what I know the car has been in some minor crash before. After some time of driving a ABS, ESC and check engine lights went on. (That was during winter time - salt, snow, moisture) I was told by a mechanic that the plug over the right front wheel, that connects cables leading from wheel speed sensor, to the main computer, was corroded. Aparently it cracked during the accident, and then the water and salt worked their way. The mechanic just cut the wires on both sides of the plug getting rid of the broken plug, and short wired them. Needles to say, it didn't work out, nothing changed and he told me that it is probably the speed sensor that's shot.
Now I have to fix it to get my emmisions done, but I want to do it as inexpensive as possible. Could you tell me exactly what those codes stand for (P0304, and P0501)? Those are the codes I got from the dealer and from the testing station.
I can get the sensor with connecting cables, from ebay @ $70-80. Can I repair it myself, or what to say to mechanic, I don't wanna be spending $$$ on diagnose, as I already have it.
Thank you for your help.
ANSWER: P0304 indicates there is a misfire on cylinder #4. This could be caused by anything from a spark plug or wire to an engine mechanical issue.
P0501 indicates a problem with the vehicle speed sensor to the engine control module (ECM). Presuming you have a 1999 or newer V6, this sensor is indeed the right front wheel speed sensor. But the lack of a signal doesn't necessarily mean the speed sensor itself is defective. There could be a problem in the wiring anywhere between the sensor, the ABS module, and the ECM. Or there could be a problem with the tone wheel on the axle shaft.
The information you've provided seems to suggest that the problems have yet to be fully and properly diagnosed. Anytime I hear "it's probably X," it sounds to me that the proper tests to determine what is and is not working have yet to be completed. In the case of the vehicle speed sensor, a proper diagnosis will include a visual inspection of the tone wheel and a check of the wiring to between the ECM, ABS module, and speed sensor to be sure it has continuity and is not shorted. Once that is verified (or if the sensor has been checked and its resistance is significantly out of specification), then it's a reasonable conclusion that the speed sensor is the problem. Additionally, since you say the mechanic wired the sensor directly into the harness, it's possible it has been wired backward. It may also be a useful exercise to switch the wires and see if the problem persists. In addition, since you have ABS, it'll be necessary to verify the ABS module actually powers up and operates. If the ECM cannot receive the vehicle speed signal from the ABS module, you'll have the same symptoms and code. Additionally, you've provided no information that indicates the cause of the misfire is known.
I'd say it's still in your best interests to spend money on diagnosis lest you spend money making repairs that won't correct the problem. Your best bet is to find a very good driveability mechanic or shop and explain the issue. It should be clear that the money you're spending is for actual diagnosis, not guesswork, unless there's some reason this isn't economically advantageous. (For example, if your spark plugs are worn and there's no other obvious misfire-related problem, they should be replaced prior to additional diagnostic effort being made on the misfire. It'd be silly to continue diagnostics once a problem is found that is consistent with the the condition.)
If you decide you wish to replace the sensor, you should expect that if your Sonata is a model year 2005 or older, this will be a difficult repair. The sensors tend to seize in the steering knuckle, making them hard to remove. The last few I've done, it's been quickest to remove the axle from the hub and hammer the sensor out from the back. In addition, the mounting screw for the sensor often breaks on attempts to remove, making it necessary to redrill and tap the hole in the knuckle to securely attach the new sensor with a new bolt.
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QUESTION: Thank you for your detailed and very helpful answer. I was just wondering if a regular tune-up could help with the misfire issue? The car is a 2006 Sonata V6 (around 65K miles), and I believe there was never a tune-up made on it. I will probably do it, and see if the problem still ocures. Unfortunatelly I got no idea on what to do with the speed sensor, I guess I'll have to get a mechanic to figure it out somehow.
Another question is what is a fair price for a tune-up for my car?
Thank you sir, you are a great help to all of us!
AnswerThe tune-up (replacement of spark plugs) could help with the misfire, but it may not. The intake plenum must be removed to replace the rear spark plugs, and your spark plugs are iridium, so I'd expect a proper tune-up to cost several hundreds of dollars. On the other hand, the maintenance interval on the spark plugs is 100k miles (+/- 5k), so unless there's something abnormal occurring, the plugs shouldn't need to be replaced.
