P0303 is the OBD-II code that means your engine computer has detected a misfire in cylinder 3. Manufacturer bulletins list the check engine light and rough idle as its main symptoms. The information below reflects those bulletins as of 2026-11-04.
The code names the cylinder, not the failed part. Start with simple checks and a coil swap test before you buy parts, and check whether a bulletin lists your vehicle.
What P0303 Means on Your Dashboard
P0303 is stored when the engine computer detects a misfire in cylinder 3, and it turns on the check engine light. Bulletins describe rough idle and reduced performance as the usual symptoms.
A misfire means the fuel and air in one cylinder did not burn as they should. The engine computer records which cylinder is affected, so P0303 points to cylinder 3 and not to the whole engine. The related codes work the same way. P0300 means a random or multiple cylinder misfire, while P0301 through P0306 each name a single cylinder. When the computer cannot pin the misfire to one cylinder, the code for random misfires is the one you will see.
Bulletins describe these symptoms for P0303:
- Check engine light on
- Rough idle or rough running
- Reduced performance without significant loss of power or stalling
Your car may show only some of these symptoms. A smooth engine does not rule out the code, so check the stored code even when the car seems fine.
Common Causes, and Why the Coil Is Not Always the Answer
A P0303 code can come from several faults, and the ignition coil is only one of them. The Audi bulletin warns that many misfire faults unrelated to the ignition coil can turn on the check engine light. If you suspect the coil, how to test an ignition coil covers a swap test, a spark test and a resistance check.
Repair guidance from more than one manufacturer makes the same point: the diagnosis must rule out other faults before a coil is replaced. The bulletins read for this article point to these areas:
- Ignition coils, which technicians swap between cylinders to see whether the misfire follows the coil
- Fuel level, because P0301 to P0304 stored with P1250 (fuel level too low) is likely a low-fuel problem rather than a coil fault
- Engine control module software, which the Lexus bulletin updates by reflash when the calibration is out of date
- Ignition coil boots, which an FCA service bulletin 08-027-20 replaces on all four coils for listed 2.4L MultiAir engines
The bulletins do not rank these causes by how often they occur, so this article does not rank them either. The checks in the next section tell you which area the evidence points to. Before you replace a coil, it helps to understand how to tell which cylinder is misfiring.
How to Diagnose P0303 Step by Step
Diagnose P0303 by checking the fuel level, related codes and software first, then running a coil swap test before any part is replaced. Replace only the coil that the misfire follows.
The Audi technical service bulletin sets out a workshop sequence in this order. The steps below summarize it so you can ask a shop the right questions.
- Read the stored codes from every control module, and note the conditions recorded on the code log.
- Check whether P1250 (fuel level too low) is stored together with P0301 to P0304. If it is, the bulletin says the fault is likely low fuel, not the coils.
- Review manufacturer bulletins and ECM software updates for misfires before you diagnose the code. The Lexus bulletin also confirms that the engine control module calibration is the latest one.
- Try to reproduce the complaint under the conditions in the freeze frame data, which show what the engine was doing when the code was set.
- Exchange the coils between the suspect cylinder and another cylinder, then test drive. If the misfire moves with the coil, replace only that coil.
- Recheck the repair under the same conditions that the code log recorded, such as engine speed, load and coolant temperature.
The Audi bulletin calls for a special tool to remove the ignition coils, so confirm you have the right tool before you start. The bulletin adds that a misfire that sets only during a cold start calls for a search of cold-start misfire bulletins for that model.
Is It Safe to Drive With a P0303 Code?
The Audi bulletin describes P0303 symptoms as reduced performance without significant loss of power or stalling. The bulletins do not cover a flashing check engine light, so use your owner’s manual for that case.
A steady light with the symptoms above matches the bulletin descriptions. A flashing light is a different situation, and it deserves more caution. The EPA’s consumer fact sheet on on-board diagnostics says a flashing light signals a severe misfire, advises reducing speed and seeking service as soon as possible, and warns that even a short stretch of severe misfire can seriously damage emission control parts. For the full picture, read what a flashing check engine light means. Have the car checked before you drive it far.
- Keep speed and engine load low until a shop has checked the car
- Note whether the light flashes or stays on, and when the rough running happens
- Do not replace parts before the coil swap test is done
These points do not replace your owner’s manual, which lists the warning-light rules for your model.
Model-Specific Bulletins and What They Cover
Manufacturer bulletins for P0303 apply only to the vehicles, engines and years they list. Three NHTSA-hosted bulletins show different fixes, from a coil swap test to an ECM reflash and coil replacement.
Scope matters more than the code itself. The Lexus service bulletin L-SB-0044-19 covers only RX450h models from 2016 to 2019 and RX450hL models from 2018 to 2019, so it does not apply to other Lexus models.
| Bulletin | Vehicles listed | Fix described |
|---|---|---|
| Audi TSB 2033630/2 (2014) | A3, A4, allroad, TT, A5, A5 Cabriolet and Q5 from 2008 to 2015 with 4-cylinder engines; A6 from 2012 to 2015 | Coil swap test; replace only the coil the misfire follows |
| Lexus L-SB-0044-19 (2019) | RX450h from 2016 to 2019; RX450hL from 2018 to 2019 | Confirm the fault, check ECM calibration, reflash if out of date, then replace the ignition coil |
| FCA 08-027-20 (2020) | 2.4L I4 MultiAir engines on listed Jeep, FIAT, Dodge, Chrysler and RAM models from 2015 to 2019 | Replace all four ignition coil boots, run the engine for at least 60 seconds, then recheck |
Under the Lexus bulletin, the repair falls under the Lexus Federal Emission Warranty for 96 months or 80,000 miles, whichever comes first, but only for the covered condition. Check your VIN against the bulletin list before you assume a bulletin applies, because a bulletin for one engine does not cover another.
Frequently Asked Questions
Can I drive with a P0303 code?
The bulletins describe reduced performance without significant loss of power or stalling for P0303 misfires. A flashing check engine light is a different situation and calls for less engine load and a prompt diagnosis. Your owner’s manual lists the warning-light rules for your model.
Is P0303 the same as P0300?
No. P0300 means a random or multiple cylinder misfire, while P0303 names cylinder 3 only. The Lexus bulletin lists P0301 through P0306 as separate codes, so each cylinder has its own code. A P0300 code gives less information about which cylinder is involved.
Does P0303 always mean a bad ignition coil?
No. The Audi bulletin warns that many misfire faults unrelated to the ignition coil can turn on the check engine light. Test the coils before you replace one. Exchange the coil with another cylinder, and if the misfire moves with it, replace that coil.
Does clearing the P0303 code fix the problem?
Clearing the code only turns off the light for now. If the cause is still there, the code and the misfire usually come back. Diagnose the cause first, then clear the code after the repair and watch whether it stays off.
Does a software update fix P0303?
Some manufacturer bulletins list an engine control module software update as part of the fix. The Lexus bulletin does this only after a diagnosis confirms a faulty coil and the calibration is out of date. Whether your car needs an update depends on its VIN and the bulletin list that covers it.
How do I know which bulletin applies to my car?
Start with the year, make, model and engine. Then check the bulletin’s vehicle list against your VIN, using the manufacturer or a dealer service department. A bulletin for a different engine or year does not apply, even when the code matches.
Read the code and freeze frame data first, and ask the shop to run a coil swap test before buying parts. Then check the bulletin list against your year, make, model and engine. If the light flashes or the car runs rough, have it checked promptly.
