GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Catera 🢒 Engine 🢒 Engine Controls - 3.0L (L81) 🢒 DTC P0300

Circuit Description

The crankshaft position (CKP) sensor sends pulses to the engine control module (ECM) as the reluctor wheel teeth rotate past the sensor. Besides using these pulses in order to synchronize the ignition and fuel injector operation, the ECM also times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in the crankshaft speed has occurred. A misfire causes an unexpected change in the crankshaft speed. A certain amount of acceleration and deceleration is expected between each firing stroke, but if the crankshaft speed changes are more than an expected amount, the ECM will interpret this as a misfire. The ECM continuously calculates the crankshaft position from the CKP sensor signals. This information is used in order to determine which cylinder is misfiring so that the ECM can increment the appropriate misfire counter and set the appropriate diagnostic trouble code (DTC), if necessary. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set. If the misfire is random and on multiple cylinders, DTC P0300 will set.

Conditions for Running the DTC
    • DTCs P0100, P0115, P0116, P0335, P1120, or P1220 are not set.
    • The engine speed is between 520-6,520 RPM.
    • The torque management is not active.
    • The anti-lock brake/traction control (ABS/TC) system is not active.
    • Rough road is not detected.
    • The fuel cut-off is not active, including the traction control, the deceleration, the high speed/RPM.
    • The engine has been running for longer than 5 seconds.
    • The air intake temperature (IAT) is more than -8°C (17°F).
    • The evaporative emission (EVAP) diagnosis is not active.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed.
    • A History DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic.
    • The DTC can be cleared with a scan tool

Diagnostic Aids

If DTC P1460 was also set, and if no misfire is currently present, the vehicle may have run low on fuel.

A Misfire DTC could be caused by an excessive vibration from sources other than the engine. Check for the following possible sources:

    • A tire or wheel that is out of round or out of balance
    • Variable thickness brake rotor or drum
    • An unbalanced drive shaft
    • Certain rough road conditions
    • a damaged accessory drive belt

DTC P0300 - Engine Misfire Detected

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Install the scan tool.
  2. Start the engine.
  3. Allow the engine to idle or operate within the conditions listed in the Freeze Frame Records.
  4. Monitor all of the misfire current counters with the scan tool. There are a total of 6 counters, 1 counter per cylinder.

Are any of the misfire current counters incrementing?

Go to Step 4

Go to Step 3

3

Is DTC P1460 also set?

Go to DTC P1460

Go to Step 9

4

Are any DTCs from P0201-P0206 also set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 5

5

Are any DTCs from P0301-P0306 also set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 6

6
  1. Visually and physically inspect the following items:
    2. • The vacuum hoses for splits, kinks, and proper connections
    • The throttle body and the intake manifold for any vacuum leaks
    • The crankcase ventilation valve and/or system for any vacuum leaks
    • The ECM ground--Verify that they are clean and secure.
  2. Repair as necessary.

Did you find and correct the condition?

Go to Step 10

Go to Step 7

7
  1. Inspect the fuel system for any restrictions, leaks or fuel contamination. Refer to Fuel System Diagnosis or Alcohol/Contaminants-in-Fuel Diagnosis .
  2. Repair as necessary.

Did you find and correct the condition?

Go to Step 10

Go to Step 8

8
  1. Perform the ignition system check. Refer to Electronic Ignition (EI) System Diagnosis .
  2. Repair as necessary.

Did you find and correct the condition?

Go to Step 10

Go to Diagnostic Aids

9
  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame data for this DTC and note the parameters.
  3. Clear the DTCs.
  4. Turn OFF the ignition for 15 seconds.
  5. Start the engine.
  6. Operate the vehicle within the Conditions For Running the DTC, and as close to the data observed in the Freeze Frame/Failure Records.
  7. Check for any DTCs.

Did the DTC fail this ignition?

Go to Step 2

Go to Diagnostic Aids

10
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 11

Go to Step 2

11

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK