Honda hard start, rough idle P0300

Diagnose and fix Honda hard start, rough idle P0300

If you have a Honda hard start, rough idle P0300 condition, read this post for the fix. Late model Honda engines are built with variable valve timing mechanisms that rotate the camshaft to change valve timing to reduce emissions and increase power and fuel economy. The mechanical advance/retard mechanisms are driven by oil pressure. The amount of oil pressure is controlled by the Variable Timing Control (VTC) oil control solenoid. Camshaft

Honda hard start, rough idle

Honda Oil Control Solenoid

position sensor A detects the intake camshaft angle and sends the information to the ECM. The ECM controls the VTC oil control solenoid valve as the intake camshaft angle changes. The solenoid is in electronically controlled valve that receives a pulse width modulate power signal from the ECM. The ECM regulates how long the power stays on versus off, which controls how long the valve is open versus closed. In other words, the length of the pulse determines oil pressure to the valve timing mechanism.

Proper oil and oil changes affect VTC oil control solenoid accuracy

The ECM bases its commands to the VTC oil control solenoid accuracy under the assumption that you’ve used the recommended oil viscosity and change your oil based on factory recommendations. If you use a DIFFERENT oil viscosity, you will get an incorrect result. For example; a 2009 Honda Accord requires 5W-20 motor oil for ALL temperature ranges. If you switch to 10W-30 or 5W-30, the thicker viscosity oil will provide different variable valve timing results which the ECM will see as a failure, resulting in a trouble code.

In addition, not following factory oil change recommendations can cause sludge buildup which can clog the intake screen on the oil control solenoid, restricting oil flow and causing incorrect cam timing.

What is a Honda P0300

A Honda P0300 trouble code is a random misfire. This means that the ECM can’t single out an individual cylinder as the cause of the misfire. When the misfire spreads across all cylinder look for these issues:

• Worn spark plugs

• erratic Crankshaft or camshaft position sensor data

• clogged or intermittent VTC oil control solenoid

Most common causes of Honda hard start, rough idle P0300

• clogged or intermittent VTC oil control solenoid

• Incorrect crankshaft position sensor readings

Here’s how to proceed: Start by cleaning the VTC strainer. If you

Honda hard start, rough idle

Honda oil control solenoid strainer

notice sludge buildup, that’s a sign you haven’t been changing oil according to factory recommendation and the buildup may return until the sludge is remove. After cleaning the strainer, test the oil control solenoid for power, short to ground, internal short or open. These solenoid have a high failure rate, especially when operated with a clogged strainer. Replace the oil control solenoid.

Check crankshaft position sensor for proper reference, ground and signal. See Honda technical service bulletin 09-050 here. If you replace the camshaft position sensor, you MUST perform a camshaft position sensor relearn procedure using a SCAN TOOL. If you skip this step, it’ll never operate properly.

Honda P0300

Honda crankshaft position sensor

©, 2017 Rick Muscoplat

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