What this code means
P0307 means the PCM has detected a possible misfire pattern on cylinder 7.
What the vehicle may do
- The engine may run rough, stumble, or feel weak under load.
- The MIL may illuminate or flash depending on misfire severity.
- Stop/start may be disabled while the code is active, if equipped.
Possible fault areas
- Possible ignition concerns, such as coil, spark plug, or control circuit issues.
- Possible fuel concerns, such as injector behavior, fuel quality, or fuel supply contamination.
- Possible air handling concerns, such as vacuum leaks or intake and exhaust restrictions.
- Possible engine mechanical, oiling, valvetrain, VVL, or wiring and control concerns.
Diagnostic path
Opening context
On this Ram 2500HD with the 6.4 HEMI gas engine, P0307 means the PCM is seeing a misfire pattern on cylinder 7. The truck may run rough, stumble under load, flash or turn on the MIL, and stop/start may be disabled while the code is active. Broadly, this kind of fault can come from ignition, fuel delivery, air leaks, engine mechanical issues, oiling or valvetrain concerns, or a wiring and control problem. The key is not to jump straight to a part. Start by proving whether cylinder 7 is actively misfiring, then follow the path the symptoms point you toward.
Confirm the active condition
Start with the basic system checks. Turn the ignition on, pull and record all codes, and save the captured operating data. Then drive or operate the truck under the same captured conditions from when P0307 set. During that drive, pay attention to when the misfire shows up, watch the downstream oxygen sensors while it is happening, and use the misfire monitor to confirm whether cylinder 7 is showing excessive misfires right now. If cylinder 7 is not actively showing the problem, treat it as an intermittent condition instead of forcing the rest of the pinpoint test.
Use the monitor gates as context
For this misfire monitor, the video can show the actual monitor gates. In the bay, the practical point is simple: make sure you are reproducing the operating conditions instead of testing the truck in a condition where the monitor may not behave the same way. The monitor depends on fuel level, battery voltage, temperature, learned values, engine speed, and it is disabled during a decel fuel shutoff event. The code sets when crankshaft speed variation between cylinders exceeds the calibrated limit for the current speed and load.
Check for related active or pending faults first
Next, look back at the codes you recorded. If other active or pending faults point to fuel control, ignition components, air handling, VVT, or VVL, handle those applicable diagnostics first. Those systems can create or steer a cylinder misfire diagnosis, so do not ignore them and chase cylinder 7 in isolation unless P0307 is the path left standing.
Inspect the MDS solenoid connections
With the ignition off, inspect the MDS solenoid connectors and jumper connectors. Look closely at connector seating, locks, corrosion, water intrusion, seals if equipped, bent or spread terminals, overheated terminals, terminals pushed back in the cavity, and terminal tension. If you find a connection problem, repair that condition, then verify the repair and confirm the code stays gone. If the connectors and terminals check out, keep moving down the path.
Do the broad mechanical and installation inspection
Now do a careful underhood inspection before getting deep into component testing. Check for accessory drive issues like a worn belt or a pulley that is misaligned or binding. Check CKP, CMP, and MAP sensor mounting, and make sure the connectors at the crank sensor, cam sensor, MAP sensor, throttle body, injector, ignition coil, and similar components are clean and tight. Also look for PCM power or ground corrosion, vacuum leaks, air induction or exhaust restrictions, internal engine concerns, moisture on ignition parts, fuel quantity or quality issues, bogging on a manual transmission, and overload from towing. If something is found, repair it and verify the repair. If not, continue.
Check for intake leaks
Next, check the engine and intake manifold for vacuum leaks. A leak that affects mixture can show up as a misfire, so do not skip this just because the code names one cylinder. If an intake leak is found, repair the leak and verify the repair. If there are no intake leaks, continue to fuel quality.
Check fuel quality and fuel level concerns
Check the fuel for water, the wrong fuel type, old or contaminated fuel, and low fuel. Also check for 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 the fuel checks out, move on to injector comparison testing.
Compare cylinder 7 injector pressure drop
Before opening the fuel system, release fuel pressure properly. This system can stay under constant pressure even with the engine off, and skipping that step can cause serious or fatal injury. Install the fuel pressure decay tester to the fuel rail, turn the ignition on, let pressure reach maximum and stabilize, and record that as the starting pressure. Actuate the cylinder 7 injector with the scan tool while watching the gauge, then record the ending pressure. Repeat the same test on several 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; otherwise engine damage can occur. Compare the ending pressures. If cylinder 7 looks about the same as the known-good cylinders, continue to spark testing. If cylinder 7 stands out, a smaller pressure drop points you toward debris in the fuel rail or injector that needs to be corrected. A larger pressure drop points toward a faulty or fouled injector concern. After correcting a fuel issue, verify the repair.
Check spark at the cylinder 7 coil
With the injector test finished, turn the ignition off, remove the fuel pressure decay tester, and reconnect the fuel lines before continuing. Remove the ignition coil from cylinder 7, reconnect the coil connector, disconnect the cylinder 7 injector connector, and install a spark tester on the coil. Crank the engine and look for a crisp blue spark. If the spark is crisp and blue, continue with plug and cylinder inspection. If it is not, jump to the ignition feed and control circuit checks.
Inspect the spark plug and cylinder
Turn the ignition off and remove the spark plug from cylinder 7. Inspect it for cracks, carbon tracking, oil fouling, coolant fouling, excess fuel fouling, gap out of specification, and a loose or broken electrode. Also look for 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 the cause before calling it fixed. Then verify the repair. If none of those conditions are present, keep going.
Check compression and isolate mechanical causes
Next, run a compression test on all cylinders and compare the known-good cylinders against cylinder 7. If cylinder 7 compression is within specification, continue. If it is not, perform a cylinder leak down test to separate valvetrain causes from combustion chamber causes, repair as necessary, and verify the repair.
See whether the misfire follows the spark plug
If compression checks out, swap the cylinder 7 spark plug with a known-good cylinder that is not misfiring, or replace the plug if access makes swapping impractical. Start the engine and watch the misfire monitor. If the misfire moves to the previously good cylinder, replace the spark plug. If the plug was replaced and the misfire is gone, that repair is complete pending verification. If the misfire does not move and does not go away, continue.
Clean carbon from the valvetrain and chambers
At this point, de-carbon the engine using Mopar Combustion cleaner. After driving and clearing the cleaner from the engine, erase the codes, then test drive the truck under the captured conditions. Watch the misfire monitor again. If P0307 returns, continue the diagnosis. If it does not return, cleaning the valves and combustion chambers repaired the fault, and you still finish by verifying the repair.
Check oiling and mechanical conditions that affect valvetrain operation
Next, check the engine oil level and oil condition, and look for mechanical or oiling conditions that could affect valvetrain operation. That includes oil pressure concerns, low oil level, an incorrect oil filter, dirty or deteriorated oil, contaminated oil, incorrect viscosity, aerated oil, and mechanical tolerances out of specification. If you find an oiling or mechanical issue, repair that condition, such as an oil drain-back problem, sludge, oil pump issue, pickup tube issue, or seal issue, then verify the repair. If none of those conditions are present, move to the VVL check.
Check VVL only when the symptom points there
Only take the VVL branch when the misfire happened as engine speed exceeded 5000 rpm and you suspect VVL involvement. A rocker arm stuck in Low Lift Mode may create a misfire only above 5000 rpm and may not set a separate VVL code. Before checking rocker arms, make sure the VVL solenoid O-rings are not missing or damaged, and make sure the solenoid is not leaking when off. If the VVL system has an issue, perform the appropriate VVL repair and verify the repair. If VVL checks out, continue to the camshaft, rocker arm, and spring inspection.
Inspect camshaft, rocker arms, and springs
Visually inspect the camshaft, rocker arms, and springs for excessive wear or broken parts. If you find a problem there, perform the appropriate repair and verify the repair. If that inspection does not find the cause, move to the final harness and PCM connection checks, unless the earlier spark test sent you into the ignition circuit branch.
If spark was missing, check ignition coil power feed
If cylinder 7 did not have a crisp blue spark, start the ignition circuit checks at the ASD relay output. Turn the ignition off and 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 output at the ignition coil connector. If the test light lights brightly, the feed side is good enough to move to the coil control circuit. If it does not, stop all scan tool actuations, repair the open or short to ground between the PDC and the ignition coil connector, and verify the repair.
Check the coil control command
For the coil control circuit, use a 12-volt test light connected to a 12 volt source and back probe the coil control circuit at the ignition coil connector. Keep clear of the fan, belts, pulleys, and loose clothing while cranking. Crank the engine for 5 seconds and watch the test light. If it blinks brightly, the control circuit is being commanded and the ignition coil is the supported replacement. Replace the ignition coil and verify the repair. If the light stays on constantly, check the coil control circuit for a short to ground. If it stays off constantly, check the coil control circuit for an open.
If the control light stays on, check for short to ground
If the coil control test light stayed on constantly, turn the ignition off and disconnect the PCM C2 connector. Do not probe PCM harness connectors directly, because that can damage terminals and create a poor terminal-to-pin connection. Install the GPEC Diagnostic Adaptor on the engine harness side of the PCM C2 connector, then check continuity between ground and the coil control circuit at the ignition coil connector. If continuity is present, repair the coil control circuit short to ground and verify the repair. If there is no continuity, move to the final harness and PCM connection checks.
If the control light stays off, check for an open
If the coil control test light stayed off constantly, turn the ignition off and measure resistance in the coil control circuit between the ignition coil connector and the GPEC adaptor. If resistance is below 3.0 Ohms, continue to the final harness and PCM connection checks. If resistance is not below 3.0 Ohms, repair the open or high resistance in the coil control circuit and verify the repair.
Final harness and PCM connection check
For the final connection check, disconnect all PCM connectors, any related inline connectors if equipped, and the related component connectors. Inspect every connector and terminal for proper installation, damaged locks, corrosion, water intrusion, seal damage if equipped, bent terminals, overheated terminals, terminals pushed back, spread terminals, and terminal tension. Repair anything you find. Then reconnect the PCM connectors, inline connectors, and component connectors, making sure they are fully seated and locked. Erase the code, drive or operate the truck under the monitored and set conditions, and read codes again. If P0307 returns after those checks and repairs, replace and program the PCM. If it does not return, the wiring or poor connection issue has been repaired. Either way, finish with repair verification.
Verify the repair
Keep verification separate from the category testing. After any repair, clear the code, reproduce the operating conditions, watch the misfire monitor, and confirm P0307 stays gone. The takeaway is to prove the active cylinder 7 misfire first, rule out related system faults and basic mechanical causes, then only move into injector, ignition, valvetrain, wiring, or PCM decisions when the test path supports it. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0307 is best handled by confirming the active cylinder 7 misfire first, then following the supported test path instead of guessing at parts.
For more guided automotive diagnostics, visit STEP Diagnostics.
