P0300

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

A 4X reluctor wheel is located on the front of the crankshaft. The crankshaft position sensor will send a pulse every falling edge of the 4X reluctor wheel. A misfire causes a change in crankshaft speed. The PCM times the interval between each pulse and compares each new time interval with the previous one to determine when an excessive change in crankshaft speed has occurred. A certain amount of acceleration/deceleration is expected between each firing stroke, but if the crankshaft speed changes are greater than an expected amount, the PCM will interpret this as a misfire. The PCM continuously calculates crankshaft position from the low and high resolution signals. This information is used to determine which cylinder is misfiring so that the PCM can increment the appropriate misfire counter.

CONDITIONS FOR SETTING THE DTC

^ DTCs P0100, P0102, P0103, P0107, P0108, P0117, P0118, P0122, P0123, P0335, P0336, P0500, P0502, P0601, P0742, not set.

^ Engine speed between 325 RPM and 3000 RPM.

^ Ignition voltage between 9.0 volts and 16.0 volts.

^ Engine coolant temperature between -7°C (l9°F) and l30°C (266°F).

^ Throttle angle steady within 1%.

^ ABS and Traction Control not active. Transmission not changing gears.
^ Exhaust Gas Recirculation (EGR) and Air Injection Reaction (AIR) diagnostic tests not in progress.

^ A/C clutch steady state.

^ Not in fuel shut-off or decel fuel cut-off.

^ ABS signals not exceeding rough road thresholds.

^ The PCM determines that an emission type Misfire is present.

^ The PCM determines that a catalyst damaging Misfire is present.

ACTION TAKEN WHEN THE DTC SETS

The PCM will illuminate the Malfunction Indicator Lamp (MIL) under the following conditions:

^ The PCM determines the percent of misfire over a 1000 revolution period is high enough to cause excessive tail pipe emissions. The PCM will illuminate the Malfunction Indicator lamp the next consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed.

^ The second consecutive drive trip that this diagnostic fails, under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed, this information will be stored in Freeze Frame. Any data previously stored in Freeze Frame will be copied into Failure Records and Freeze Frame will be overwritten by this DTC. The only exception to this is if a Fuel Trim DTC was already recorded in Freeze Frame. In this case, the Fuel Trim data stays in Freeze Frame and the Misfire data will be updated in Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed.

IMPORTANT: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than three drive trips. Review Freeze Frame/Failure Records for the last failure conditions.

^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

^ A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.

^ PCM battery voltage is interrupted.

^ Using a Scan tool.

DIAGNOSTIC AIDS

^ If cylinder #1 is misfiring, inspect the EGR valve for hanging open. Remove the EGR valve and inspect for contaminates. Clean the EGR as necessary. Refer to EGR Valve

^ The vehicle running out of fuel can cause sufficient misfire to set DTC P0300.

^ A misfire DTC could be caused by excessive vibration from sources other than the engine.

The following are possible sources:

- Tire/wheel out of round/balance

- Variable thickness brake rotor/drum

- Drive shaft not balanced

- Certain rough road conditions

^ For intermittents, refer to Symptoms. Testing and Inspection

TEST DESCRIPTION

Number(s) below refer to step numbers on the diagnostic table.

2. Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as water is applied.

If the Misfire Cur counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. Perform the diagnostic table for DTC P0335 first if this condition is suspected.

If misfire is present and a fuel control problem is suspected, force the system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.

5. This distributor ignition system has lower KV requirements than typical systems. The J 26792 spark tester (ST-125) may not fire consistently when testing this system. This chart only asks if the system is capable of firing the spark tester.

6. This distributor ignition system has lower KV requirements than typical systems. The J 26792 spark tester (ST-125) may not fire consistently when testing this system. This chart only asks if the system is capable of firing the spark tester.

8. If the plug is gas fouled, dry out the plug before reinstalling it in another cylinder.

19. If the customers complaint is The MIL is flashing, indicates that a Catalyst Misfire has occurred. The vehicle must be driven in the conditions to run the catalyst diagnostic. Refer to DTC P0420 TWC System Low Efficiency Bank 1 and/or DTC P0430 TWC System Low Efficiency Bank 2 for Conditions for Setting the DTC.