System Description
The Powertrain Control Module (PCM) monitors both the crankshaft and camshaft position in order to detect engine misfire. The PCM looks for the rapid decrease in crankshaft speed associated with engine misfire once every 100 camshaft revolutions. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under severe misfire, the PCM flashes the MIL. A flashing MIL signals that a misfire capable of damaging the catalytic converter is detected. The Torque Converter Clutch is disabled momentarily to determine if the misfire was due to a rough road condition (automatic transmission only).
Conditions for Setting the DTC
| • | The misfire total is greater than 12 counts. |
| • | The engine speed is between 469 RPM and 6406 RPM |
| • | The battery voltage is between 9 volts and 17 volts. |
| • | The Engine Coolant Temperature (ECT) is between -7°C (20°F) and 123°C (254°F). |
| • | The engine has been running more than 15 seconds. |
| • | The Throttle Position (TP) hasn't changed more than 8% in 1 second. |
| • | DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0601, P0742, P1133, and P1404 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 a misfire is severe enough to cause catalyst damage. |
| • | The Torque Converter Clutch (TCC) will disable whenever a misfire is being detected with or without a misfire DTC set (automatic transmission only). |
| • | The PCM will record the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn off after 3 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. |
| • | A scan tool can clear the DTCs. |
Diagnostic Aids
An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel.
Whenever the DTC is an intermittent, refer to the Driveability Symptom Tables.
Perform the fuel Injector Balance Test. Refer to Fuel Injector Balance Test .
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 Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. This information on the scan tool can be referred to later.
-
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. |
| • | Check the throttle body mounting area and intake manifold sealing surfaces for air leaks. |
-
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.
-
If the misfire is not present, operate the vehicle within the the conditions recorded 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.
-
Check the fuel for contamination (water, alcohol, etc).
-
A basic engine problem that affects all cylinders is the only possibility at this point (e.g. cam timing, throttle body leak, restricted air flow, etc.) Refer to the Engine Mechanical portion of the service manual.
-
Tests the ignition system voltage output using a spark tester J 26792.
-
Replace any spark plugs that are worn, cracked or fouled. Refer to the Ignition System portion of the service manual if any plugs are fouled or damaged due to an engine mechanical malfunction.
-
Checks for voltage at the ignition feed circuit.
-
When the fuel injector 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.
-
Since the voltage is supplied to the fuel injector on a single circuit, the malfunction could only be a poor electrical connection or an open in the fuel injector electrical harness. An open before the harness would result in a Cranks But Will Not Run complaint.
-
Before replacing the PCM, check the terminals for improper mating, broken locks, or physical damage to the wiring harness. The replacement PCM must be reprogrammed and the crankshaft position system variation learn procedure must be performed. Refer to the latest Techline procedures for PCM reprogramming and to the Powertrain Control Module (PCM) for the Crankshaft Position System Variation Procedure .
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
2 | Install a scan tool. Is DTC P0200 set? | -- | ||
Were any repairs necessary? | -- | |||
4 | Start the engine and allow the engine to idle. Are any Misfire Current counters incrementing? | -- | ||
Are all counters equal (within a percentage of each other)? | -- | |||
Are any Misfire Current counters incrementing? | -- | Go to Diagnostic Aids | ||
7 |
Is the fuel pressure within the specified range? | 284-325 kPa (41-47 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? | -- | -- | |
Was spark observed on all four spark plug cables? | -- | |||
Replace any malfunctioning spark plugs. Were any malfunctioning? | -- | |||
Does the fuel injector test light blink? | -- | |||
14 | Perform the Fuel Injector Solenoid Coil Test . Are the fuel injectors OK? | -- | ||
15 |
Did the test light illuminate? | -- | ||
16 | Replace any malfunctioning fuel injector(s). Is the action complete? | -- | -- | |
17 | Check the affected 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? | -- | -- | ||
Repair the open ignition feed circuit between the fuel injector harness electrical connector and the fuel injector electrical connector. 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? | 30000ohms | ||
21 |
Notice: Do not leave the jumper wire connected to the PCM IC circuit connector for longer than 5 seconds at a time. Failure to do so may damage the ignition coil and/or the Ignition Control Module. Is spark present when the jumper is removed from the IC circuit? | -- | ||
22 |
Was a repair necessary? | -- | ||
23 | Remove the ignition coil from the cylinder that did not spark. Using a DVM measure the secondary coil resistance. Is the secondary coil resistance within the specified value? | 5-8K ohms | ||
24 |
Was spark observed on the spark tester? | -- | ||
25 | Check for poor electrical connections, if OK replace the ICM. Is the action complete? | -- | -- | |
26 | Inspect the PCM electrical connector and connections. Are the electrical connections OK? | -- | ||
Replace the PCM. Is the action complete? | -- | -- | ||
28 | Replace the spark plug cable. Is action complete? | -- | -- | |
29 | Replace the malfunctioning ignition coil. Is the action complete? | -- | -- | |
30 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
31 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to Applicable DTC Table | System OK |
