P0303

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 Convener 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 Convener 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 tan 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.

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 in the scan tool for later reference.

2. Whenever a DTC P0108 is present, verify that no misfire is present by viewing the misfire counters. DTC P0108 may set as a result of a misfire.

3. A visual/physical inspection should include checking the following conditions:

^ The wiring for proper connections, pinches and cuts.

^ Clean and tight PCM grounds.

^ The 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 throttle body mounting area and intake manifold sealing surfaces.

4. This step determines if DTC P0303 is the result of a hard failure or an intermittent condition.

6. When the misfire is not present, operate the vehicle to the conditions found 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. Whenever the misfire accumulators start 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.

10. No spark on one coil, may be caused by an open secondary circuit. Therefore, the coil's secondary resistance should be checked.

13. Use injector test light J 34780-2 to test the harness wiring and for PCM control of the injectors.

14. Perform the injector Coil Test Procedure on the misfiring cylinder only.

16. Determines if the injector driver circuit is shorted to ground or voltage or if the PCM is faulty.

20. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.

22. 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.

27. Since voltage is supplied to the injector on a single circuit before the injector harness, the fault could only be a poor connection or open in the injector harness. An open before the harness would result in a Cranks But Won't Run complaint.

28. A basic engine problem that affects only cylinder #3 is possible at this point (i.e. valve train, compression, etc.).