P0309: Misfire detected in cylinder 9
Cylinder 9 misfire
Severity: Severity not verified — if the car runs badly, have it inspected
The two sources that define this code do not rate how urgent it is, so the severity is not verified. Misfire can overheat the catalytic converter, so have it checked soon and treat a flashing check engine light as urgent.
P0309 in short
P0309 means the engine computer detected misfires in cylinder 9. TroubleCodes.net points to that cylinder's spark plug, ignition coil, wiring or fuel injector, then compression problems such as exhaust valves or a head gasket leak. Swapping parts with a working cylinder shows which part is at fault.
P0309 is stored when the engine computer sees that cylinder 9 is not firing as it should. The Delaware DMV code list gives the title 'Cylinder 9 Misfire Detected'.
Because the fault is in one cylinder, TroubleCodes.net says to look at parts that serve only that cylinder: the spark plug, ignition coil, wiring and fuel injector. If those are fine, compression problems such as exhaust valves or a leaking head gasket come next.
The misfire monitor leans heavily on the crankshaft position sensor, so a faulty sensor can produce false misfire readings. Cylinder 9 exists only on engines with nine or more cylinders.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Spark plug, ignition coil or wiring on cylinder 9
Common general cause- Why it ranks here
- TroubleCodes.net lists the spark plug, ignition coil and wiring first for a single-cylinder misfire.
- What would change this
- Rises if the misfire follows the part when it is swapped with another cylinder. Falls if it stays on cylinder 9.
Cause 2: Fuel injector on cylinder 9
Common general cause- Why it ranks here
- TroubleCodes.net names the fuel injector among the single-cylinder causes, after the ignition parts.
- What would change this
- Rises if ignition parts are proven good and the injector is clogged or not firing. Falls if the injector tests normal.
Cause 3: Low compression on cylinder 9 (exhaust valves, head gasket)
Possible — needs testing- Why it ranks here
- TroubleCodes.net says to test compression when swapping parts does not move the misfire, and to suspect a head gasket if there is overheating or coolant loss.
- What would change this
- Rises if compression is low or coolant is disappearing. Falls if compression is even.
Cause 4: Faulty crankshaft position sensor giving false misfire readings
Possible — needs testing- Why it ranks here
- TroubleCodes.net notes the misfire monitor relies heavily on this sensor, so a bad one can set misfire codes; it ranks low because it would usually affect more than one cylinder.
- What would change this
- Rises if several cylinders show misfires or the sensor has its own codes. Falls if only cylinder 9 is affected.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: With the engine off and cool, swap cylinder 9's ignition coil or spark plug with that of a working cylinder, clear the codes and drive until the monitor runs again.
Warning:Engine off and key out when removing coils or plugs; ignition voltage can shock you and a hot engine can burn you. Start plugs by hand to avoid cross-threading.
IfThe misfire code moves to the other cylinder
It meansThe swapped part is faulty.
Points to: Spark plug, ignition coil or wiring on cylinder 9
IfThe misfire stays on cylinder 9
It meansCheck the injector and compression.
Step 2: Run a compression test on cylinder 9 and compare it with the other cylinders.
Warning:Plugs come out of a warm engine hard and can burn you; disable fuel and ignition before cranking so fuel does not spray and coils do not shock you.
IfCylinder 9 is clearly lower than the rest
It meansA mechanical fault such as a valve or head gasket is likely.
Points to: Low compression on cylinder 9 (exhaust valves, head gasket)
IfCompression is even
It meansTest the injector, wiring and crankshaft position sensor.
Symptoms
- Vibration at idle
- Reduced engine performance
- Worse fuel economy
How to fix
On your vehicle
DodgeYour car
2003 · Ram
Supported by vehicle dataNHTSA bulletin summary for this model: covers a MIL with erroneous codes in the P0300-P0309 range. Whether it is still current is not verified.
1801403Status unverified
MIL on and erroneous codes P0300-P0309
2003ram · issued · NHTSA 10001523
MIL on with erroneous diagnostic codes in the P0300-P0309 range. Only the NHTSA flat-file summary was read, not the bulletin itself.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
No curated relationships for P0309 yet.
Sources and review
- P0309 – Cylinder 9 Misfire Detected
- P0309: NHTSA bulletin 10001523 (MIL on and erroneous codes P0300-P0309)
- On-Board Diagnostic Trouble Codes (generic code title list)
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
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