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Chevrolet: Rough Running Engine and DTC P0300

Some customers may complain of a rough running engine and the check engine light is on. You may find DTC P0300 (Engine Misfire Detected) set along with a misfire and low compression in one or more cylinders.

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Models 

2016-2017 Chevrolet Malibu 1.5L (LFV) 

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Figure 1: Examples of pistons with varying levels of damage. 

Concern

Some customers may complain of a rough running engine and the check engine light is on. You may find DTC P0300 (Engine Misfire Detected) set along with a misfire and low compression in one or more cylinders.

Figure 2: Examples of light vertical marks visible on the cylinder wall: None of the marks in the cylinder walls could be felt with the fingernail and engine replacement is not recommended.

Cause

The condition may be caused by a damaged piston.


Figure 3: Example of a damaged cylinder wall.

Correction

Repair the engine mechanical concern based on the results of the Service Procedure testing below. This bulletin does not apply to 2017 vehicles built with VIN sequence HF214702 and higher as they have the updated piston assemblies installed. To isolate the source of cylinder leakage to a valve or cylinder sealing issue, it may be necessary to remove the intake and exhaust manifolds.

If low compression is found, perform cylinder leakage testing in the service information and record the test results to isolate the concern. If excessive leakage to the crankcase is isolated, check piston and cylinder wall condition.

Figure 4: In this example, the scuffing is wide and has removed the cross-hatch from the cylinder wall in the area above the arrow. This would result in oil consumption and requires engine replacement.

If the cylinder wall surface has not been compromised, replace all four piston and rod assemblies. Fill the crankcase with current specification Dexos oil. Check that the vehicle is up to the latest released calibration available. If not, reprogram the engine control module (ECM).

An unmetered air leak in the induction system, or an engine mechanical issue causing rough running, may cause the ECM to learn an incorrect Throttle Body Idle Airflow Compensation value over time.

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This incorrectly learned value may cause various symptoms to occur such as MIL on with P1101 setting, rough or unstable idle speeds and/or engine stall.

Once the mechanical repairs have been completed, perform a throttle body inspection and cleaning, followed by a throttle body idle relearn and air flow compensation reset function with a scan tool.

Article courtesy Underhood Service.

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