P0302

Diagnostic Chart:

Wiring Diagram:

SYSTEM DESCRIPTION

The Powertrain Control Module (PCM) monitors crankshaft and camshaft position to detect if the engine is misfiring. The PCM looks for a quick drop in crankshaft speed. This test is executed in blocks of 100 camshaft revolution tests. It may take between one to several tests to store a DTC and illuminate the Malfunction Indicator Lamp (MIL). Under light misfire conditions, it may also take more than one trip to set a DTC. Severe misfire will flash the MIL indicating that catalyst damage is possible. The Torque Converter Clutch is disabled momentarily to determine if the misfire was due to a rough road condition (automatic trans. only).

CONDITIONS FOR SETTING THE DTC

^ Misfire total is greater than 12 counts.

^ Engine speed is between 469 RPM (automatic trans.) or 750 RPM (manual trans.) and 3400 RPM

^ Battery voltage is between 9 volts and 17 volts.

^ Engine Coolant Temperature (ECT) is between -7°C (20°F) and 123°C (254°F).

^ Engine has been running more than 15 seconds.

^ Throttle Position (TP) hasn't changed more than 8% in 1 second.

^ DTC(s) P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0502, P0503, P0601, P0742, P1133, and P1406 not set.

ACTION TAKEN WHEN THE DTC SETS

^ The Malfunction Indicator Lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles when there is misfire.

Or

^ The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

Or

^ The MIL will illuminate immediately and flash if misfire is severe enough to cause catalyst damage.

^ Torque Converter Clutch (TCC) is disabled when misfire is present (automatic only).

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

^ A history DTC is stored.

^ Coolant fan turns ON.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.

^ A history DTC will clear after 40 consecutive warm up cycles without a fault.

^ DTC(s) can be cleared by using a scan tool.

DIAGNOSTIC AIDS

An intermittent can also be the result of a defective reluctor wheel. Remove crankshaft sensor and inspect reluctor wheel through sensor mount hole. Check for porosity and condition of wheel.

Verify electronic Ignition Control Module (ICM) 11 pin harness connector terminal K, CKT 750 resistance is less than 0.5 ohms.

If DTC is intermittent, refer to Symptoms. Testing and Inspection

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.

2. If a DTC P0200 is present, the condition causing misfire is in the injector circuitry. The DTC P0200 table will diagnose the injectors and circuitry.

3. A visual/physical inspection should include checking:

^ Wiring for proper connections, pinches and cuts.

^ PCM grounds for being clean and tight.

^ Vacuum hoses for splits, kinks and proper connections as shown on the Vehicle Emission Information label. Check thoroughly for any type of leak or restriction.

^ For air leaks at the intake manifold sealing surface.

4. This step determines if DTC P0302 is the result of a hard failure or an intermittent condition.

5. If a plug boot is burned, the other plug on that ignition coil may still fire at idle. This step tests the system's ability to produce at least 25,000 volts at each spark plug.

6. If the misfire is not present it may be necessary to duplicate the conditions in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. If the misfire accumulators starts to increment, then misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared. The current counter must count a total of at least 195 misfires before writing to the history counter.

7. Spark is available at the misfiring cylinder. At this point the misfire is being caused by a spark plug or a basic engine problem.

8. A basic engine problem that affects only cylinder #2 is possible at this point (i.e. valve train, compression, etc.).

9. Replace any spark plugs that are worn, cracked or fouled. Refer to ENGINE if any plugs are fouled or damaged due to an engine mechanical failure. Engine

10. No spark, on one coil, may be caused by an open secondary circuit. Therefore, the coil's secondary resistance should be checked. Resistance readings above 20,000 ohms, but not infinite, will probably not cause a no start but may cause an engine miss under certain conditions.

11. If the no spark condition is caused by coil connections, a coil or a secondary boot assembly, the test light will blink.

13. The ignition coil harness can easily be checked by performing the previous step with the ignition coil harness connected to the ICM. Check for a voltage and ground signal to the ignition coils at the ignition coil electrical connector.

15. Refer to Ignition Coils for service of the ignition system.

16. Refer to Ignition Coils for service of the ignition system. Ignition System

19. Refer to Ignition Control Module for service of the ignition system. Ignition Control Module

20. Any circuitry, that is suspected as causing the complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.

22. Conditions for setting the DTC P0420 need to be run to determine if the catalyst has been damaged from the misfire.