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Code P0300 means the computer is seeing misfires in the enigne. Code P0174 means lean condition on Bank 2, the even numbered cylinders. With these two codes the thing you need to look for first is a vacuum leak on bank 2 (front cylinders)
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Here are the charts for these codes if they help you.
CIRCUIT DESCRIPTION To provide the best possible combination of driveability, fuel economy and emission control, a Closed Loop air/fuel metering system is used. While in Closed Loop, the PCM monitors the heated oxygen sensor signal voltage and adjust fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the long and short fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0%; if heated oxygen sensor signal is indicating a lean condition, the PCM will add fuel, resulting in a fuel trim above 0%, 100% is maximum lean. If a rich condition is detected, the fuel trim values will be below 0%, -99% is maximum rich, indicating that the PCM is reducing the amount of fuel delivered. If an excessively lean condition is detected, the PCM will set DTC P0174.CONDITIONS FOR SETTING THE DTC Test Conditions
Failure Condition The PCM detects the average fuel trim cell values are greater than 1.125 for short term fuel trim and 0.992 for long term fuel trim for 2.5 seconds.ACTION TAKEN WHEN THE DTC SETS
CONDITIONS FOR CLEARING THE MIL/DTC
DIAGNOSTIC AIDS If the scan tool indicated the test ran and passed, the fault is not present. If the scan tool indicated that the test did not run, ensure that all the test conditions were met.TEST DESCRIPTION Number(s) below refer to the step number(s) on the Diagnostic Table.
Here is for code P0300
CIRCUIT DESCRIPTION This diagnostic test is used to detect misfires in any cylinder. A misfire occurs when there is a complete lack of or poor combustion in the cylinder. A misfire will cause a fluctuation in crankshaft revolution speed. The PCM uses the time between 4X reference pulses to determine when these fluctuations occur. At lower engine speeds, fluctuations in crankshaft speed are measured each reference pulse to detect misfire. At higher engine speeds, fluctuations in crankshaft speed are monitored over two engine revolutions and fluctuations in crankshaft speed at each half revolution are compared to compute a balance number. The 4X reference pulses originate in the ignition control module and vary with RPM.CONDITIONS FOR SETTING THE DTC Test Conditions
Failure Condition A misfire has been detected.ACTION TAKEN WHEN THE DTC SETS The PCM will turn on the SERVICE ENGINE SOON MIL under the following conditions.
PCM turns ON the ENGINE MISFIRE message. The PCM will record operating conditions at the time the DTC Sets. This information will be stored in the Freeze Frame and Failure Records.CONDITIONS FOR CLEARING THE MIL/DTC
TEST DESCRIPTION Number(s) below refer to the step number(s) on the Diagnostic Table.