What this code means
P0305 means the PCM has detected a possible misfire on cylinder 5.
What the vehicle may do
- The engine may run rough or shake.
- The MIL may illuminate or flash depending on misfire severity.
- Stop/start may be disabled while the code is active on equipped vehicles.
- The concern may be more noticeable under certain load or speed conditions.
Possible fault areas
- Possible ignition faults may include the coil, plug, or related control wiring.
- Possible fuel faults may include injector operation, fuel quality, or fuel supply concerns.
- Possible air and sensor-related areas may include vacuum leaks, air handling, and sensor mounting or connection problems.
- Possible mechanical areas may include compression, oiling, carbon buildup, coolant or oil entering the cylinder, camshaft, rocker arm, spring, VVT, or VVL concerns.
- A PCM-related issue can be possible after the rest of the diagnostic path has been checked.
Diagnostic path
Open: What P0305 is telling us
On this 2019 to 2024 Ram 1500DT with the 5.7 HEMI, P0305 means the PCM has detected a misfire on cylinder 5. In the bay, this may show up as a rough run, a flashing or illuminated MIL depending on severity, and stop/start may be disabled while the code is active. Broadly, a cylinder-specific misfire can come from ignition, fuel delivery, air leaks, mechanical sealing, carbon buildup, valvetrain or cam control issues, wiring, or in rare cases the PCM side of the circuit. The key is not to jump straight to a part. Start with the basic system checks, then prove whether the misfire is active and follow the path in order.
Monitor gates and how the code sets
Before chasing the fault, make sure the monitor had a valid chance to run. The misfire monitor is gated by fuel level above 12%, battery voltage above 10.9 volts, ambient temperature above -23°C (-9.4°F), coolant temperature at engine start above -7°C (19.4°F), or after a colder start when engine temperature reaches 21°C (69.8°F). Engine speed is between approximately 400 rpm and 6200 rpm, and the monitor is disabled during a decel fuel shutoff event. The code sets when the crankshaft speed variation between cylinders exceeds a calibrated value for the current speed and load.
Confirm the misfire is active
Turn the ignition on, read and record all codes and captured operating data, then try to reproduce those same conditions. During the road test, pay attention to when the cylinder 5 misfire shows up because that timing matters later. Watch the downstream oxygen sensors while the misfire is occurring, and use the misfire monitor to see which cylinders are actually counting misfires. If cylinder 5 is showing excessive misfires now, continue. If it is not, treat it as an intermittent condition instead of forcing the test path.
Check for other active systems before the cylinder workup
Next, look at the codes you recorded. If there are active or pending faults tied to fuel control, ignition components, air handling, VVT, or VVL, handle those first because they can create the cylinder misfire you are seeing. If those related systems are not setting active or pending faults, move into the misfire inspection.
Do the broad mechanical and connection inspection
Now do a careful inspection before breaking out deeper tests. Look for accessory drive problems like belt wear or pulley misalignment and binding. Check that the crank, cam, and MAP sensors are mounted correctly, and look closely at connector and terminal condition at the crank sensor, cam sensor, MAP sensor, throttle body, injector, ignition coil, PCM powers and grounds, and related components. Also check for vacuum leaks, intake or exhaust restriction, signs of internal engine trouble, moisture on ignition parts, poor or insufficient fuel, and load-related conditions like bogging or towing overload. If you find a real problem here, repair it and verify the repair. If not, keep going.
Check intake leaks and fuel quality
Check the engine and intake manifold for vacuum leaks. If the intake system is leaking, repair the leak and verify the repair. If the intake checks out, check fuel quality and supply condition: water in the fuel, wrong fuel type, old or contaminated fuel, and low fuel. The path also calls for checking proper ethanol level in the gasoline. If the fuel is the problem, replace the fuel and, if needed, flush and clean the fuel system, then verify the repair. If fuel checks clean, continue to injector testing.
Compare injector pressure drop
Before opening or servicing any fuel hose, fitting, or line, release fuel system pressure. The system can stay under constant pressure even with the engine off, and this is a serious safety point. Install the Fuel Pressure Decay Tester 8978A at the fuel rail. Turn the ignition on, let pressure reach maximum and stabilize, and record that as the starting pressure. Command the cylinder 5 injector with the scan tool while watching the gauge, then record the ending pressure. Repeat the same test on several known-good cylinders, always starting each injector actuation from the same starting pressure. After each injector actuation, start the engine to clear fuel from the cylinder so you do not risk engine damage. If the ending pressures are about the same, move on to spark. If cylinder 5 stands out, a small pressure drop points toward debris in the rail or injector, and a large drop points toward a faulty or fouled injector. Repair as necessary and verify the repair.
Check spark at the cylinder 5 coil
Shut the ignition off, remove the pressure decay tester, and reconnect the fuel lines before continuing. Remove the ignition coil from the misfiring cylinder, reconnect the coil connector, disconnect that cylinder’s fuel injector connector, and install a spark tester on the coil. Crank the engine and look for a crisp blue spark. Keep clear of the fan, pulleys, and belts any time the engine is operating or being cranked, and avoid loose clothing. If the spark is crisp and blue, inspect the plug and cylinder. If it is not, jump to the coil feed and control circuit checks.
Inspect the spark plug and cylinder
With the ignition off, remove the spark plug from cylinder 5 and inspect it closely. Look for cracks, carbon tracking, oil fouling, coolant fouling, excess fuel, gap out of specification, or a loose or broken electrode. Also look for signs of oil or coolant in the cylinder. If any of those plug conditions are present, replace the spark plug. If oil or coolant is in the cylinder, diagnose and repair that cause, then verify the repair. If the plug and cylinder inspection do not show those problems, keep going.
Check compression, then see if the plug fault follows
Run a compression test on all cylinders and compare the known-good cylinders against cylinder 5. If compression is not within specification, perform a cylinder leak-down test to determine whether the issue is in the valvetrain or combustion chamber, repair as necessary, and verify the repair. If compression is within specification, swap the spark plug with a known-good cylinder that was not misfiring, or replace it if access makes the swap impractical. Start the engine and watch the misfire monitor. If the misfire follows the plug, replace that spark plug and verify the repair. If the misfire goes away after replacing the plug, the repair is complete after verification. If it does not move or go away, continue.
Carbon cleaning and oiling checks
If the plug did not prove out, de-carbon the engine using Mopar Combustion cleaner. After driving and clearing the cleaner from the engine, erase the codes, test drive under the captured conditions, and watch the misfire monitor. If the misfire does not return, the valve and combustion chamber cleaning repaired the fault, and you still finish with repair verification. If the misfire returns, check engine oil level and condition, oil pressure concerns, mechanical tolerances, filter correctness, dirty or contaminated oil, wrong viscosity, and aerated oil. If any of those conditions are present, repair the oiling or mechanical issue and verify the repair. If not, continue to the VVL and valvetrain checks.
VVL and valvetrain checks
If the misfire showed up when engine speed exceeded 5000 rpm and VVL is suspect, check VVL operation before going deeper into mechanical teardown. The described VVL logic says that with the solenoid off and no oil flow to the rocker arms, the system should be in high lift mode, and that one rocker arm stuck in low lift can cause a misfire at or above approximately 5000 rpm without necessarily setting a VVL code. Before checking rocker arms, make sure the solenoid O-rings are not missing or damaged and that the solenoid is not leaking when off. One caution here: this part of the path names cylinder one while we are diagnosing P0305 on cylinder 5. Do not simply transpose that detail. Pause, recheck the earlier diagnostic path, confirm the correct cylinder and hardware path, and avoid guessing. If no VVL issue is found, visually inspect the camshaft lobes, rocker arms, and springs for excessive wear or broken parts. Repair any confirmed VVL or valvetrain issue as necessary and verify the repair. If nothing is found, continue to the final harness and PCM-side checks.
If spark was missing: check coil feed and control
If the cylinder 5 coil did not produce a crisp blue spark, start at the ASD Relay (F342) output circuit. With the ignition off, disconnect the ignition coil connector. Turn the ignition on, actuate the ASD relay with the scan tool, and use a 12-volt test light connected to ground to probe the ASD Relay (F342) output at the coil connector. If the light does not illuminate brightly, stop scan tool actuations, repair the open or short to ground between the PDC and the coil connector, and verify the repair. If the feed is good, connect the 12-volt test light to a 12 volt source, back probe the coil control circuit at the coil connector, and crank the engine for 5 seconds. If the light blinks brightly, the control is present and the path supports replacing the ignition coil, then verifying the repair. If the light stays on constantly, check the coil control circuit for a short to ground. If the light stays off constantly, check for an open or high resistance.
Coil control circuit integrity
For the short-to-ground check, turn the ignition off, disconnect the PCM C2 connector, and install the GPEC Diagnostic 10436 adapter on the engine harness side. Do not probe the PCM harness connectors directly; doing that can damage the PCM terminals and create a poor terminal-to-pin connection. Check continuity between ground and the coil control circuit at the ignition coil connector. If continuity to ground is present, repair the short to ground and verify the repair. If there is no continuity to ground, move to the open-circuit check. Measure resistance in the coil control circuit between the ignition coil connector and the GPEC adapter. If resistance is below 3.0 Ohms, continue to harness connection checks. If it is not below 3.0 Ohms, repair the open or high resistance and verify the repair.
Connector checks and final decision
At this point, disconnect the PCM connectors, any related in-line connectors if equipped, and the related component connectors. Inspect connector installation, locks, corrosion, water intrusion, weather seals, bent terminals, overheated terminals, pushed-back terminals, spread terminals, and terminal tension. Repair any condition found, then reconnect everything fully seated and locked. Erase the codes and operate the vehicle under the same monitored and set-condition window. If P0305 returns after the circuit, connector, fuel, ignition, air, and mechanical paths have checked out, the path supports replacing and programming the PCM, followed by repair verification. If the code does not return, the wiring or poor connection problem has been repaired. The takeaway is simple: prove the misfire is active, isolate fuel, spark, air, mechanical, and control circuits in order, then verify the fix under the same conditions. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0305 is best handled by confirming the active cylinder misfire first, then testing fuel, spark, air, mechanical condition, and control circuits in order.
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