For 1990-2009 cars

Table 1: | DTC P0301 - Cylinder 1 Misfire Detected

### Circuit Description

The crankshaft position (CKP) sensor sends pulses to the engine control module (ECM) as the reluctor wheel teeth rotate past the sensor. Besides using these pulses in order to synchronize the ignition and fuel injector operation, the ECM also times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in the crankshaft speed has occurred. A misfire causes an unexpected change in the crankshaft speed. A certain amount of acceleration and deceleration is expected between each firing stroke, but if the crankshaft speed changes are more than an expected amount, the ECM will interpret this as a misfire. The ECM continuously calculates the crankshaft position from the CKP sensor signals. This information is used in order to determine which cylinder is misfiring so that the ECM can increment the appropriate misfire counter and set the appropriate diagnostic trouble code (DTC), if necessary. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set. If the misfire is random and on multiple cylinders, DTC P0300 will set.

### Conditions for Running the DTC

• | One or more of the following DTCs are not set: P0100, P0115, P0116, P0120, P0121, P0335, P0336

• | The engine speed is between 520 RPM and 6,400 RPM.

• | The load signal meets the following criteria:

Engine Speed (RPM) | Load Signal (ms)
--- | ---
1000 | 1.0
2000 | 1.1
3000 | 1.1
6400 | 2.7

• | The load signal change is less than 1.5 milliseconds per cylinder event.

• | The Torque Management is not active.

• | The ABS/TC is not active.

• | Rough Road is not detected.

• | The fuel cutoff is not active (including the traction control, the deceleration, the high speed/RPM ).

• | The engine has been running for longer than 5 seconds.

• | The IAT is greater than -8°C (17°F).

• | The EVAP diagnosis is not active.

### Conditions for Setting the DTC

• | A misfire that is more than the legislated limit, an amount of misfire ranging from 1.0-12.5 percent.

• | The above conditions met for at least 5 camshaft revolutions.

### Action Taken When the DTC Sets

• | The ECM will illuminate the malfunction indicator lamp (MIL) under the following conditions:

- | The ECM determines that the percentage of misfire is high enough in order to cause catalyst damage. The ECM will flash the MIL during the time that the catalyst damaging misfire is present. The ECM will switch OFF the injector, a maximum of 2, related to the misfiring cylinder, and the MIL will illuminate continuously.

- | The ECM determines that the percentage of misfire is high enough in order to cause excessive tail pipe emissions. The ECM illuminates the MIL on the next consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions, the load, the RPM, the temperature, as the MIL illuminated in the previous ignition cycle.

• | The first drive trip that this diagnostic fails, shows a reading of Fail Pending, this information will store in the Freeze Frame. Any data that was previously stored in the Freeze Frame will be overwritten by the Freeze Frame data for this DTC. The only exception to this is if a Fuel Trim DTC was already recorded in the Freeze Frame. In this case, the fuel trim data stays in the Freeze Frame and the Misfire data will not store.

### Conditions for Clearing the MIL/DTC

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

| Important: If the fuel cutoff was active as a result of catalyst damaging misfire, and a catalyst damaging misfire no longer exists, the fuel cutoff can only be deactivated by a new ignition cycle.

• | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed.

• | A History DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic.

• | The ECM battery voltage is interrupted.

• | Cleared by a scan tool

### Diagnostic Aids

A Misfire DTC could be caused by an excessive vibratration from sources other than the engine. Check for the following possible sources:

• | Tire/wheel out of round/balance

• | Variable thickness brake rotor/drum

• | Drive shaft not balanced

• | Certain rough road conditions

### Test Description

The number(s) below refer to the step numbers on the diagnostic table:

1. Wetting down the secondary ignition system with water from a spray bottle may help in order to locate the damaged or deteriorated components. Look/listen for any arcing or any misfiring when you apply water.

   If the Misfire Current counter is 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.

#### DTC P0301 - Cylinder 1 Misfire Detected

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install the scan tool.
2. Start the engine.
3. Allow the engine to idle at the normal operating temperature.
4. Monitor the Misfire Current counter for this cylinder with the scan tool.

Is the Misfire Current counter incrementing?

--

Go to Step 3

Go to Step 4

3 | Visually/physically inspect the following items:

• | The vacuum hoses for splits, kinks and proper connections.

• | The throttle body and the intake manifold for vacuum leaks.

• | The crankcase ventilation valve and/or system for vacuum leaks.

• | The ECM grounds for being clean and secure.

• | Check that all of the injector harness connectors are connected to the proper injector/cylinder.

• | Check that the ignition wires are connected to the proper cylinders.

Was a problem found and corrected?

--

Go to Step 9

Go to Step 5

4 |

1. Turn on the ignition with the engine off.
2. Review the Freeze Frame data for this DTC and note parameters.
3. Clear the DTCs.
4. Turn off the ignition for 15 seconds.
5. Start the engine.
6. Operate the vehicle within the conditions that were required for this diagnostic to run, and as close to the conditions that were recorded in the Freeze Frame as possible. Refer to Conditions for Running the DTC.
7. Check for any DTCs.

Is this DTC set?

--

Go to Step 5

Refer to Diagnostic Aids

5 | Use the Spark Tester J 26792 (ST-125) in order to check for a spark on the affected cylinder while cranking the engine. Is the spark present? | -- | Go to Step 6 | Go to Ignition System Check
6 | Check the spark plug for signs of oil or coolant fouling. Was a problem found? | -- | Refer to Engine Mechanical | Go to Step 7
7 | Check the spark plug for the following conditions:

• | Cracks/damage

• | Excessive wear

• | An improper gap (If an improper gap is found, and the plug is reusable, be sure to re-gap the spark plug by using a wire type gauge, J 41319).

• | Carbon tracking on the insulator (replace the affected wire also, if this is found).

Was a problem found and corrected?

--

Go to Step 9

Go to Step 8

8 | Check the compression and perform a leak down test on the affected cylinder. Refer to Engine, General Information for procedures. Was a problem found and corrected? | -- | Go to Step 9 | Go to Fuel Injector Balance Test .
9 |

1. Clear the DTCs with the scan tool.
2. Turn off the ignition for 15 seconds.
3. Operate the vehicle with the conditions that are required for this vehicle to run. Refer to Conditions for Running the DTC.
4. Check for any DTCs.

Is this DTC set?

--

Go to Step 2

Go to Step 10

10 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | The System is OK