Part Two

Control System DTCs

DTC Troubleshooting: P0300, P0301, P0302, P0303, P0304

DTC P0300 : Random Misfire Detected
DTC P0301 : No. 1 Cylinder Misfire Detected
DTC P0302 : No. 2 Cylinder Misfire Detected
DTC P0303 : No. 3 Cylinder Misfire Detected
DTC P0304 : No. 4 Cylinder Misfire Detected

27. Check Cylinder Leakage

-1. Perform a cylinder leakage test. Engine Compression Test and Cylinder Leakage Test

-2. Record your test results in the chart shown below.

Does any cylinder have leakage greater than 10 %?
-YES- If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed, and then perform the Repair Confirmation.
-NO- The cylinders are sealing properly. Go to step 28.

28. Check Cylinder Compression

-1. Perform a cylinder compression test. Engine Compression Test and Cylinder Leakage Test

-2. Record your test results in a chart similar to the one shown below.

Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-YES- The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed, and then perform the Repair Confirmation.
* Incorrect camshaft timing.
* A bent (short) connecting rod.
* Worn or damaged camshaft lobes.
-NO- The engine compression and cylinder leakage is normal. Go to step 29.

29. Exchange Fuel Injector

-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.

-2. Drive the vehicle under the conditions when the misfire was duplicated.

-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE

Do the misfire counts stay on the problem cylinder after the fuel injector is swapped?
-YES- The fuel injector is OK. All of the failures have been checked for this type of misfire. Go to step 1 in the Failure Confirmation procedure and ensure you selected the correct troubleshooting procedure.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then perform the Repair Confirmation.

30. Inspect Spark Plug

-1. Remove the spark plug from the problem cylinder.

-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.

Does the spark plug show any signs of failure or is it not the correct part number?
-YES- Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 31.

31. Check Ignition Coil Spark

-1. Turn the ignition switch to LOCK (0).

-2. Remove the ignition coil from the problem cylinder.

-3. Connect a commercially available spark tester between the ignition coil and engine ground.

-4. Start the engine with the ignition coil connected.

Does the ignition coil produce a spark?
-YES- The ignition coil wiring is OK. Go to step 39.
-NO- There is a problem with the ignition coil wiring. Go to step 32.

32. Exchange Ignition Coil

-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.

-2. Connect a commercially available spark tester between the ignition coil and engine ground.

-3. Start the engine with the ignition coil connected.

Does the ignition coil produce a spark?
-YES- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then perform the Repair Confirmation.
-NO- There is a problem with the ignition coil circuit. Go to step 33.

33. Check Ignition Coil Power and Ground

-1. Disconnect the ignition coil 3P connector from the problem cylinder.

-2. Turn the ignition switch to ON (II).

-3. Measure the voltage between ignition coil 3P connector terminals No. 1 (power) and No. 2 (ground).

Is there battery voltage?
-YES- The ignition coil power and ground circuits are OK. Go to step 34.
-NO- There is a problem with the ignition coil power or ground circuit. Go to step 38.

34. Check Ignition Coil Control Short to Power

-1. Turn the ignition switch to ON (II).

-2. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.

Is there about 4 V or more?
-YES- The ignition coil control circuit is shorted to power. Go to step 35.
-NO- The ignition coil control circuit is not shorted to power. Go to step 36.

35. Isolate Ignition Coil Control Short to Power

-1. Jump the SCS line with the HDS.

-2. Turn the ignition switch to LOCK (0).

-3. Disconnect the ECM/PCM connectors.

-4. Turn the ignition switch to ON (II).

-5. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.

Is there about 4 V or more?
-YES- There is a short to power on the ignition coil control circuit. Find and repair the failure, and then perform the Repair Confirmation.
-NO- The ECM/PCM is malfunctioning. Replace the ECM/PCM Service and Repair, and then perform the Repair Confirmation.

36. Check Ignition Coil Control Open Circuit

-1. Jump the SCS line with the HDS.

-2. Turn the ignition switch to LOCK (0).

-3. Disconnect the ECM/PCM connectors.

-4. Check for continuity between the ignition coil control terminal at the ECM/PCM connector and at the ignition coil 3P connector terminal No. 3.

Is there continuity?
-YES- The ignition coil control circuit is not open. Go to step 37.
-NO- Repair the open circuit between the ignition coil and the ECM/PCM, and then perform the Repair Confirmation.

37. Check Ignition Coil Control Short to Ground

-1. Check for continuity between the ignition coil control terminal at the ignition coil 3P connector terminal No. 3 and body ground.

Is there continuity?
-YES- Repair the short to ground on the ignition coil control wire, and then perform the Repair Confirmation.
-NO- The ignition coil control wiring is OK. Substitute a known-good ECM/PCM Service and Repair, and then perform the Repair Confirmation.

38. Check Ignition Coil Power Circuit

-1. Measure the voltage between ignition coil 3P connector terminal No. 1 (power) and a known-good engine ground.

Is there battery voltage between the ignition coil power terminal and engine ground?
-YES- The power circuit is OK. Repair the open circuit between the ignition coil (3P connector terminal No. 2) and G101, and then perform the Repair Confirmation.
-NO- Repair the open circuit between the ignition coil and the ignition coil relay, and then perform the Repair Confirmation.

39. Inspect Ignition Coil

-1. Inspect the ignition coil and spark plug tube for engine oil contamination.

Is the ignition coil covered in engine oil?
-YES- Clean the oil from the ignition coil and spark plug tube. Replace the spark plug tube seals in the cylinder head cover Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 40.

40. Exchange Spark Plug and Ignition Coil

-1. Exchange the spark plug and the ignition coil with a normally operating cylinder.

-2. Drive the vehicle under the conditions when the misfire was duplicated.

-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE

Did the misfire counts stay on the problem cylinder?
-YES- The ignition coil and spark plug are OK. Go to step 42.
-NO- There is a failure in the ignition coil or the spark plug. Go to step 41.

41. Exchange Ignition Coil

-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.

-2. Drive the vehicle under the conditions when the misfire was duplicated.

-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE

Did the misfire counts stay on the problem cylinder?
-YES- The spark plug has a failure. Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then perform the Repair Confirmation.

42. Check MAP Sensor Fluctuation

-1. Start the engine, and let it idle until the cooling fans cycle twice.

-2. Turn off all engine and electrical loads (AC, radio, lights, etc.).

-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.

-4. Begin displaying live vehicle data on a line graph.

-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.

-6. Watch the MAP SENSOR fluctuation. See examples below.

Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
-YES- The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 43.
-NO- The intake manifold vacuum fluctuation is OK. Go to step 46.

43. Adjust Valve Clearance

-1. Adjust the valve clearances Adjustments, and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 °F (38 ° C) before adjusting the valve clearance. Short cutting this step may cause incorrect valve clearance and engine misfire.

-2. Recheck the MAP Sensor fluctuation at idle.

Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
-YES- Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 44.
-NO- The excessive MAP sensor fluctuation was caused by incorrect valve clearance. Perform the Repair Confirmation.

44. Check Cylinder Leakage

-1. Perform a cylinder leakage test. Engine Compression Test and Cylinder Leakage Test

-2. Record your test results in the chart shown below.

Does any cylinder have leakage greater than 10 %?
-YES- If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed, and then perform the Repair Confirmation.
-NO- The cylinders are sealing properly. Go to step 45.

45. Check Cylinder Compression

-1. Perform a cylinder compression test. Engine Compression Test and Cylinder Leakage Test

-2. Record your test results in a chart similar to the one shown below.

Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-YES- The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed, and then perform the Repair Confirmation.
* Incorrect camshaft timing.
* A bent (short) connecting rod.
* Worn or damaged camshaft lobes.
-NO- The engine compression and cylinder leakage is normal. Go to step 46.

46. Exchange Fuel Injector

-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.

-2. Drive the vehicle under the conditions when the misfire was duplicated.

-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE

Do the misfire counts stay on the problem cylinder after the fuel injector is swapped?
-YES- The fuel injector is OK. Go to step 47.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then perform the Repair Confirmation.

47. CKP Pattern Clear/Pattern Learn

-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.

-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern.

-3. Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts.

-4. Drive the vehicle under the conditions when the misfire was duplicated.

-5. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE

Did the misfire counts stay on the problem cylinder?
-YES- Update the ECM/PCM with the latest software ECM/PCM Update or substitute a known-good ECM/PCM Service and Repair, and then perform the Repair Confirmation.
-NO- Perform the Repair Confirmation.

48. Inspect Spark Plug

-1. Remove the spark plug from the problem cylinder.

-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.

Does the spark plug show any signs of failure or is it not the correct part number?
-YES- Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 49.

49. Check MAP Sensor Fluctuation

-1. Start the engine, and let it idle until the cooling fans cycle twice.

-2. Turn off all engine and electrical loads (AC, radio, lights, etc.).

-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.

-4. Begin displaying live vehicle data on a line graph.

-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.

-6. Watch the MAP SENSOR fluctuation. See examples below.

Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
-YES- The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 50.
-NO- The intake manifold vacuum fluctuation is OK. Go to step 53.

50. Adjust Valve Clearance

-1. Adjust the valve clearances Adjustments, and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 ° F (38 ° C) before adjusting the valve clearance. Short cutting this step may cause incorrect valve clearance and engine misfire.

-2. Recheck the MAP Sensor fluctuation at idle.

Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine hot?
-YES- Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 51.
-NO- The excessive MAP sensor fluctuation was caused by incorrect valve clearance. Perform the Repair Confirmation.

51. Check Cylinder Leakage

-1. Perform a cylinder leakage test. Engine Compression Test and Cylinder Leakage Test

-2. Record your test results in the chart shown below.

Does any cylinder have leakage greater than 10 %?
-YES- If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed, and then perform the Repair Confirmation.
-NO- The cylinders are sealing properly. Go to step 52.

52. Check Cylinder Compression

-1. Perform a cylinder compression test. Engine Compression Test and Cylinder Leakage Test

-2. Record your test results in a chart similar to the one shown below.

-3. Tighten the EGR valve nuts.

-4. Operate the vehicle under the conditions where the misfire was duplicated.

Did the misfire counts stop or significantly reduce?
-YES- A leaking EGR valve is causing the misfire. Replace the EGR valve Service and Repair, and then perform the Repair Confirmation.
-NO- The misfire is not caused by a leaking EGR valve. Go to step 54.

54. Check Fuel Pressure

-1. Relieve the fuel pressure. Service and Repair

-2. Attach the fuel pressure gauge set and the fuel pressure gauge. Testing and Inspection

-3. Locate and record the fuel pressure specification for your vehicle.

-4. Start the engine and record the fuel pressure under the conditions the misfire was duplicated.

Is the fuel pressure within specifications?
-YES- The fuel pressure is OK. Go to step 55.
-NO- Check for pinched or damaged fuel lines. If OK, replace the fuel tank unit Fuel Tank Unit Removal/Installation, and then perform the Repair Confirmation.

55. Check Fuel Contamination

-1. Remove the fuel tank unit. Fuel Tank Unit Removal/Installation

-2. Inspect for evidence of fuel contamination such as diesel fuel, water, rust, or debris.
NOTE: If the misfire occurred shortly after refueling, the likely cause is poor fuel quality. The MIL DIST (MIL distance) value in the DATA LIST, along with the fuel level, can help you make this determination.
Incorrect or contaminated fuel typically affects multiple cylinders. But a problem such as water in the fuel can cause a single cylinder misfire that occurs randomly.

Is there evidence of fuel contamination?
-YES- Replace the fuel filter and then drain/refill the fuel tank with a known-good fuel. Perform the Repair Confirmation.
-NO- The fuel system has no signs of fuel contamination. Go to step 56.

56. Check MAF Sensor g/s

-1. Locate and record the MAF SENSOR g/s specification for your vehicle. This can be found in troubleshooting procedure for DTC P0171.

-2. Ensure the vehicle meets these conditions:
* Engine coolant temperature (ECT SENSOR 1) above 176 °F (80 °C)
* A/T in P or N, M/T in neutral
* All electrical loads off

-3. Monitor the ENGINE SPEED in the DATA LIST with the HDS. Raise and hold the engine speed steady at the specified rpm.

-4. While holding the rpm steady, check the MAF SENSOR in the DATA LIST.

Is the MAF Sensor g/s value within specifications?
-YES- The MAF sensor is reading correctly. Replace the fuel injectors Service and Repair, and then perform the Repair Confirmation.
-NO- The MAF sensor is not reading correctly. Replace the MAF sensor/IAT sensor Service and Repair, and then perform the Repair Confirmation.

57. Inspect Spark Plug

-1. Remove the spark plug from the problem cylinder.

-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.

Does the spark plug show any signs of failure or is it not the correct part number?
-YES- Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 58.

58. Inspect Ignition Coil

-1. Inspect the ignition coil and spark plug tube for engine oil contamination.

Is the ignition coil covered in engine oil?
-YES- Clean the oil from the ignition coil and spark plug tube. Replace the spark plug tube seals in the cylinder head cover Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 59.