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Narrow down the symptoms and solutions to fix your engine issues
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If your OBD-2 scanner has pulled up a cylinder 3 misfire error and you see the P0303 code, it indicates that one of the cylinders in your engine isn’t combusting fuel properly. This is one of the most notoriously confusing errors to diagnose and clear, but if you’re patient and take your time there’s a good chance you’ll be back on the road in no time. Here, we’ll walk you through what this code means, why it’s significant, and what you can do to diagnose and fix the issue.
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Section 5 of 5:
Diagnostics & Solutions
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Deal with any other error codes first. If there are multiple error codes on your OBD-2 reader, the P0303 code could be a byproduct of some other underlying problem—not the main issue itself. For example, if your crankshaft needs to be replaced, the cylinder is just going to keep misfiring (even if you clear the code) if you don’t deal with the crankshaft.
- Check the freeze frame data in your OBD2 scanner. This will give you the timeline of the error codes. Deal with and fix every error occurring before the P0303 cylinder 3 misfire, first.
- The freeze frame data might be confusing if this is the first time you’ve looked at it. Basically, it’s a list of all events in your engine. Start at the top and write down every error code or acronym. Then, look online to determine what they refer to. This should give you a list of repairs you need to make.
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Replace the spark plugs if they’re dirty or damaged. Disconnect the battery to avoid shocking yourself. Then, remove any spark plug wires or connectors that feed into the engine above each cylinder. Remove the wire plug by gripping it and gently lifting it up. Slide a long socket wrench down the hole into the spark plug housing. Unscrew it and remove the spark plug. Repeat this process for every spark plug and replace them . [9] X Research source
- Always replace each of the spark plugs at the same time. When one goes bad, it’s a sign the others will go bad soon.
- If you aren’t sure whether the spark plugs are to blame, test the plug in cylinder 3 by swapping it out with the plug in cylinder 4 or 2. If that new cylinder misfires, you’ve confirmed the spark plugs are to blame.
- A new set of spark plugs is likely to run $100-250, although it may be a bit more if you need new wiring done by a mechanic.
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Inspect the ignition coils and replace them as needed . If the spark plugs appear to be fine or the problem persists, your ignition coils are the next most likely culprit. Locate the coils between the battery and the distributor or ECM. Swap the cylinder 3 coil and cylinder 4 coil, and start the engine. If cylinder 4 misfires, replace the bad ignition coil and reassemble the spark plug assembly.
- If you have an ignition coil railing where they’re all connected, unlock the railing and replace the entire system.
- You can test the ignition coils by performing a spark test or by using a multimeter if you’d like.
- If you go to a mechanic, ignition coil replacements will cost $200-700 depending on your car's make and model.
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Look for loose connections or wires. If you can’t find the problem in the spark plugs or coils, go around your engine bay and inspect all of the cables and connections. Make sure everything is plugged in entirely and replace any frayed cables or blown fuses. If you’re especially handy and know how to work on your vehicle, you could also try: [10] X Research source
- Resetting your camshaft sensor .
- Checking your timing chain for damage and replacing it if necessary .
- Cleaning the MAF sensor or swapping it out for a replacement .
- Cleaning your fuel injectors or replacing them with new ones .
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See a mechanic to check for fuel system issues and engine damage. There’s only so much that you’ll be able to do on your own, and the P0303 error code is notorious for having a ton of potential causes. If you still can’t identify the cause of the misfiring cylinder, tow your car to a mechanic. They’ll be able to isolate the problem and fix it. [11] X Research source
- The cost of these repairs by a mechanic will vary depending on the specific components you need to change. Expect to spend anywhere from $250-1,200. The most expensive repair will be a new fuel pump.
- Vacuum leaks are also relatively pricey. These could run $150-1,000.
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Tips
- If the check engine light is still on after you’ve fixed the problem, try completing a drive cycle first to see if the light goes away. [12] X Research sourceThanks
- You can reset your check engine light using your OBD-2 scanner. The indicator is just going to come back on if there’s still an error, though. [13] X Research sourceThanks
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References
- ↑ https://www.dmv.de.gov/VehicleServices/inspections/pdfs/dtc_list.pdf
- ↑ https://www.dispatch.com/story/business/2015/09/26/car-talk-despite-mistrust-get/24013737007/
- ↑ https://cartreatments.com/engine-misfire-symptoms/
- ↑ https://cartreatments.com/engine-misfire-symptoms/
- ↑ https://www.dispatch.com/story/business/2015/09/26/car-talk-despite-mistrust-get/24013737007/
- ↑ https://www.dispatch.com/story/business/2015/09/26/car-talk-despite-mistrust-get/24013737007/
- ↑ https://www.dispatch.com/story/business/2015/09/26/car-talk-despite-mistrust-get/24013737007/
- ↑ https://www.dispatch.com/story/business/2015/09/26/car-talk-despite-mistrust-get/24013737007/
- ↑ https://static.nhtsa.gov/odi/tsbs/2019/MC-10161643-0001.pdf
- ↑ https://static.nhtsa.gov/odi/tsbs/2019/MC-10161643-0001.pdf
- ↑ https://www.repairsmith.com/blog/mechanic-shop-near-me/
- ↑ https://static1.squarespace.com/static/59970b344c0dbfc24e10d9a5/t/59c9637f32601e31bf2c3f68/1506370436958/MASS-Module_4-2012_Update.pdf
- ↑ https://www.caranddriver.com/features/a25063304/reset-check-engine-light/
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