Refer to
Ignition 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 the reluctor wheel.
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 in the scan tool for later reference.
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When a DTC P0108 is present, verify that no misfire is present by viewing the misfire counters. DTC P0108 may set as a result of misfire.
-
A visual/physical inspection should include checking the following components:
| • | The wiring for proper connections, pinches or cuts. |
| • | The PCM grounds for being clean and tight. |
| • | 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. |
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This determines if DTC P0300 is the result of a hard failure or an intermittent condition.
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When all the accumulators are relatively equal, then the misfire is being caused by something that affects the entire engine. When they are not then the misfire is being caused by something that is specific to two or more cylinders.
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Whenever the misfire is not present operating the vehicle 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. Whenever 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.
-
Check fuel for water, alcohol, etc.
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A basic engine problem that effects all cylinders is the only possibility at this point. (I.e. cam timing, throttle body leak, restricted air flow, etc.) Refer to Section 6A .
-
Tests the harness wiring and for PCM control of the fuel injectors using injector test light J 34780-2.
-
Checks for voltage at the ignition feed circuit.
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Whenever the driver circuit is shorted to ground, the light will be ON steady. When the driver circuit is shorted to voltage or open, the light will be OFF.
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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.
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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.
-
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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Are any component DTCs set? | -- | Go to DTC Tables first | ||
Were any repairs necessary? | -- | |||
Are any Misfire Current counters incrementing? | -- | |||
Are all counters equal (within a small percentage of each other)? | -- | |||
Are any Misfire Current counters incrementing? | -- | Go to Diagnostic Aids | ||
7 |
Is the fuel pressure within the specified value? | 214-303 kPa (31-44 psi) | Go to Fuel System Diagnosis | |
Check the fuel for contamination. Is the fuel OK (uncontaminated)? | -- | |||
Check for a basic engine problem. Is the action complete? | -- | -- | ||
10 | Replace the contaminated fuel. Is the action complete? | -- | -- | |
Does the injector test light blink? | -- | |||
12 | Perform the Injector Coil Test Procedure , refer to Fuel Injector Solenoid Coil Test Are the fuel injectors OK? | -- | ||
Did the test light illuminate? | -- | |||
14 |
Was spark observed on all four spark plug cables? | -- | ||
15 |
Are the frequency readings within the specified values? | 1-10 Hz | ||
16 | Replace any faulty fuel injector(s). Is the action complete? | -- | -- | |
17 | Check the effected fuel injector driver circuit(s) for an open, short to ground or short to voltage. Was a problem found? | -- | ||
Repair the open or the shorted fuel injector driver circuit(s). Is the action complete? | -- | -- | ||
Replace the PCM. Is the action complete? | -- | -- | ||
20 | Measure the resistance of the spark plug cable that the spark plug tester did not spark. Is the resistance of the spark plug cable less than the specified value? | 30000 ohms | ||
21 |
Is the voltage less than the specified value? | 0.5V | ||
22 | Remove the ignition coil from the cylinder that did not show a frequency response. Using a DVM measure the secondary coil resistance. Is the secondary coil resistance within the specified value? | 5-8 K ohms | ||
23 |
Does the test light? | -- | ||
24 |
Was spark observed on the spark tester? | -- | ||
25 | Repair the open in the effected ignition control circuit. Is the action complete? | -- | -- | |
26 | Repair the open ignition feed circuit. Is the action complete? | -- | -- | |
27 | Repair the short to voltage in the effected ignition control circuit. Is the action complete? | -- | -- | |
28 | Replace the ICM. Is the action complete? | -- | -- | |
Replace any faulty spark plugs. Is the action complete? | -- | -- | ||
30 | Replace the faulty ignition coil. Is action complete? | -- | -- | |
Replace the PCM. Is the action complete? | -- | -- | ||
32 | Replace the spark plug cable. Is the action complete? | -- | -- | |
33 |
Was a problem found? | -- | ||
34 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
35 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC Table | System OK |
