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Rob
Rob, ASE Master Technician
Category: Car
Satisfied Customers: 255
Experience:  GM World Class Technician, Senior Master Subaru Technician, 18 years experience
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1997 Cadillac: p0174 &

Resolved Question:

What is causing a P0174 & P0300 on a 1997 Cadillac, what do I need to do to fix this?
Submitted: 6 years ago.
Category: Car
Expert:  Rob replied 6 years ago.

HiCustomerwelcome to Just Answer!

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)

Please let me know if you need further help.

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Here are the charts for these codes if they help you.

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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

  • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0121, P0122, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0143, P0144, P0146, P0151, P0154, P0562, P0163, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0300, P0325, P0327, P0340, P0401, P0506, P0507, P1121, P1133, P1153, P1154, P1441, P1442, P1508 and P1509 are not set.
  • Closed loop enabled.
  • Engine Coolant Temperature between 84.5°C (184°F) and 105°C (221°F).
  • Barometric Pressure greater than 70.8 kPa.
  • Mass Air Flow between 3 and 200 grams per second.
  • Manifold Absolute Pressure between 27 and 103.2 kPa.
  • Intake Air Temperature between -40°C (-40°F) and 151°C (304°F).
  • Engine speed between 400 and 3000 RPM.
  • Throttle angle less than 19.8%.
  • Vehicle speed less than 70 mph.
  • EVAP canister purge tank not full (PCM estimation).
  • Fuel trim enabled.

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

  • The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
  • The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC

  • The PCM will turn the MIL OFF after three consecutive drive trips within the same driving parameters that set the DTC and the diagnostic runs and does not fail.
  • A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
  • A History DTC will clear after eighty drive cycles within the same driving parameters that set the DTC with no failures of any emission related diagnostic test.
  • PCM battery voltage is interrupted.
  • Using a Scan tool.

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.

  1. Freeze frame data will aid in locating a hard to find malfunction. For example, if the fault only occurs at high speed, this would be determined by monitoring the fuel trim cells. The fuel trim cell for cruise could be above 95%, which indicates a lean condition. The freeze frame will also indicate how many miles ago the condition was present.
  1. If DTC P0171 is also set indicates both banks are operating lean. Inspect items that would cause both banks to operate lean.

Here is for code P0300

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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

  • DTC(s) P0101, P0102. P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0340 and P0502 are not current or have not set since last key ON.
  • Coolant is between -7°C (19°F) and 128°C (262°F).
  • Engine speed running for at least 3.19 seconds.
  • Engine speed is less than 6375 rpm.
  • Traction control is not present.
  • Cylinder shut down is not present
  • Ignition voltage is between 9 and 16 volts.
  • Throttle angle 0.3 degrees or more.
  • Vehicle speed is less than 45 mph.
  • During a 12.5 millisecond time period throttle angle stays between 0.6 and 1 degrees.
  • During a 100 millisecond time period throttle angle stays between 0.96 and 1.28 degrees.
  • Delta MAP diagnostic not in progress.
  • Number of consecutive positive delta revolution mode indexes less than 20.
  • Number of consecutive negative delta revolution mode indexes less than 20.
  • A/C compressor clutch has not changed states in the last 100 milliseconds.
  • Slip speed is at least -64 rpm.
  • 18 engine cycles have occurred since any of above conditions and were not met.
  • Rough road indication is not considered present.
  • 16 engine cycles have occurred since power-up.
  • 16 engine cycles have occurred since both the reference mode and revolution mode were disabled.
  • 8 engine cycles have occurred since a CAM error, or an ignition system error.
  • Diagnostic tool not connected.
  • 10 engine cycles have occurred since desired torque less than 95.3%.

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.

  • Impending catalytic converter damage
  • If a cylinder misfires at a sufficiently high rate for at least 200 engine revolutions, a catalytic converter damaging misfire level is considered present and the Service Engine Soon MIL will flash until the catalyst damaging condition is no longer present, at which time the MIL will remain on steady.
  • Disable TCC if either the number of emission misfires or number of catalyst damaging misfires exceeds 2.
  • Excessive exhaust emissions
  • It a cylinder misfires 15 times in 200 revolutions for 5 out of 16 200 revolution tests in each of two consecutive trips (engine run cycles which meet specific criteria), an excessive exhaust emissions condition is considered present and the Service Engine Soon MIL will be turned on.
  • Disable TCC if either the number of emission misfires or number of catalyst damaging misfires exceeds 2.

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

  • The PCM will turn the MIL OFF after three consecutive drive trips within the same driving parameters that set the DTC and the diagnostic runs and does not fail.
  • A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
  • A History DTC will clear after eighty drive cycles within the same driving parameters that set the DTC with no failures of any emission related diagnostic test.
  • PCM battery voltage is interrupted.
  • Using a Scan tool.

DIAGNOSTIC AIDS

  • If more than one cylinder showed a history of misfire, look for something in common between the cylinders such as, shared coil, etc. If only one cylinder showed a history of misfire look for a possible vacuum leak at that cylinder, etc.
  • If fault cannot be duplicated, wet secondary ignition system and operate vehicle under conditions that the DTC set.
  • It is possible to set DTC P0300 if the vehicle has run out of or is very low on fuel.
  • To quickly determine the cylinder(s) that are misfiring. use the scan tool and observe Misfiring Cyl. in the Misfire data list. This will display the primary and secondary misfiring cylinders.
  • Due to the potentially destructive nature that engine misfire has on the exhaust catalyst always check for proper catalytic converter operation after a misfire has been repaired. This can be accomplished in the following ways:
  • Drive the vehicle under the Test Conditions for DTC P0420 and ensure that the DTC runs and passes.
  • In IM240 areas (or those properly equipped) perform the Catalytic Converter Service Bay Test.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. If other DTCs are set, diagnose them first because other problems may be causing the misfire.
  2. Checking if multiple cylinders are misfiring. If there is a single cylinder misfiring, the diagnosis is much easier.
  3. Checking for causes of a single cylinder misfire.
Rob, ASE Master Technician
Category: Car
Satisfied Customers: 255
Experience: GM World Class Technician, Senior Master Subaru Technician, 18 years experience
Rob and 16 other Car Specialists are ready to help you
Customer: replied 6 years ago.
The motor was running when died. I towed out of street & read the codes P0174 & P0300. I got your reply. I went & cleared the codes & the motor started and ran for about 1 minet & died. it set no codes and restarted and is running now.

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