Refer to
Ignition Controls
and
Fuel Controls
for wiring view.
System Description
The Powertrain Control Module (PCM) monitors both the crankshaft and the camshaft position in order to detect an engine misfire. A rapid decrease in the crankshaft speed indicates misfire. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and before illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under a severe misfire, the PCM flashes the MIL. A flashing MIL indicates that there is a misfire that is capable of damaging the catalytic converter. The torque converter clutch (TCC) disables momentarily in order to determine if the misfire was due to a rough road condition, automatic transmission 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) illuminates if the fault is active within the same conditions for two out of eighty ignition cycles and a misfire is present. |
| OR |
| The MIL illuminates after two consecutive ignition cycles during in which the diagnostic runs with the fault active |
| OR |
| The MIL illuminates immediately and flashes if a misfire is severe enough to cause any catalyst damage. |
| • | In vehicles with automatic transmission only, the torque converter clutch (TCC) is disablesd when a misfire is present. |
| • | The PCM records the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed. |
| • | A history DTC clears after 40 consecutive warm up cycles without a fault. |
| • | Clear the MIL/DTCs with 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. Refer to DTC P0300 Engine Misfire Detected .
Verify the electronic Ignition Control Module (ICM) 11 pin harness connector terminal K, ground circuit should have less than 0.5 ohms of resistance.
If DTC is intermittent, refer to Symptoms .
When checking the electrical terminal connections with a test light or DMM, a malfunctioning electrical terminal connection maybe cleaned and not detected as a problem. You may also clean a corroded or dirty electrical terminal connection when disconnecting and reconnecting any electrical connector.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
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.
-
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.
-
A visual/physical inspection should include checking:
-
This step determines if DTC P0300 is the result of a hard failure or an intermittent condition.
-
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. The history counter begins counting after the DTC is set. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared.
-
If all the accumulators are relatively equal, then the misfire is being caused by something that affects the entire engine. If they are not then the misfire is being caused by something that is specific to two or more cylinders.
-
A basic engine problem that effects more than cylinder. (i.e. cam timing, compression, etc.) Refer to Section 6A . Also a possible fuel injector problem might exist. Refer to Fuel Injector Balance Test and Fuel Injector Solenoid Coil Test .
-
After repairs, verify no misfire by duplicating the conditions within Freeze Frame Data while watching the misfire counters.
-
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.
-
Replace any spark plugs that are worn, cracked or fouled. Refer to Section 6A if any plugs are fouled or damaged due to an engine mechanical failure.
-
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.
-
If the no spark condition is caused by coil connections, a coil or a secondary boot assembly, the test light will blink.
-
Refer to Ignition Coils for on vehicle service of the ignition system.
-
Refer to Ignition Coils for on vehicle service of the ignition system.
-
If the resistance is high, then the IC circuit is open or the PCM is faulty.
-
Refer to Ignition Control Module Replacement for on vehicle service of the ignition system.
-
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.
-
Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.
-
Conditions for setting the DTC P0420 need to be run to determine the catalyst has been damaged from the misfire.
| • | 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 throttle body mounting area and intake manifold sealing surfaces. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Install a scan tool. Was a DTC P0200 set? | -- | |||
Were any repairs necessary? | -- | |||
With the engine idling. Are any Misfire Current counters incrementing? | -- | |||
Are any Misfire Current counters incrementing? | -- | |||
Are all counters equal (within a small percentage of each other)? | -- | |||
7 |
Is the fuel pressure within the specified value? | 211-304 kPa (31-44 psi) | ||
8 | Check the fuel for water, alcohol or other contamination. Is the fuel OK (uncontaminated)? | -- | ||
Is the action complete? | -- | -- | ||
Replace the contaminated fuel. Is the action complete? | -- | -- | ||
Does the spark tester spark on all the cylinders? | -- | |||
Check for any faulty spark plugs in the cylinders that indicated misfire and replace if necessary. Were any spark plugs faulty? | -- | |||
Is the resistance less than the specified value? | 10 K ohms | |||
Does the test light blink? | -- | |||
15 | Remove the ignition coil from the ignition coil housing and recheck the resistance between the secondary terminals of the ignition coils. Is the resistance less than the specified value? | 10 K ohms | ||
16 | Repair the open or short in the ignition coil harness, poor ignition coil connection or replace the ignition coil, ignition coil housing or boot assembly. Is the action complete? | -- | -- | |
17 | Visually inspect the ICM 11 pin harness connector to see if the connections are clean and tight and repair as necessary. Were any repairs necessary? | -- | ||
Is the action complete? | -- | -- | ||
Replace the affected ignition coil. Is the action complete? | -- | -- | ||
Is the resistance between the specified value? | .6-2.6 K ohms | |||
Replace the ICM. Is the action complete? | -- | -- | ||
22 | Inspect the PCM connector and connections. Are the connections OK? | -- | ||
23 | Check the affected cylinders ignition control circuit for an open or a short and repair as necessary. Was a repair necessary? | -- | ||
Repair the connector or connections. Is the action complete? | -- | -- | ||
Replace the PCM. Is the action complete? | -- | -- | ||
Does the scan tool indicate that these diagnostics have ran and passed? | -- | |||
27 | Check if any additional DTC's are set. Are any DTC's set that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
