I have a 99 Silverado 4x4 with the 5.3l and automatic. A couple of days ago I started it in the morning and it would rev up to almost 2k then drop to about 500. I thought it was going to die out so I tried to keep some light gas pedal to keep the rpm up a little. No help at all. The engine would rev but wouldn't maintain a steady idle. As it warmed up, the idle was ok and driveability wasn't a problem. It set codes for the SES. I stopped at autozone and got three codes. P0171, P0174, and P0300. What do I need to do for further troubleshooting? It seems that there is a wide range of what it might be. My truck has 4 o2 sensors. Surely they can't all be bad in one try. Any ideas are appreciated.
The Crankshaft Position sensor is mounted through the side of the engine block at the rear of Bank 2 above the starter assembly. The Crankshaft Position sensor works in conjunction with a 24X reluctor wheel on the crankshaft. The reluctor wheel is inside the engine immediately in front of the rear main bearing. The PCM provides a 12 volt power supply to the CKP sensor as well as a ground and a signal circuit.
A misfire causes a change in crankshaft speed. The PCM 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 crankshaft speed has occurred. You can expect a certain amount of acceleration/deceleration between each firing stroke, but if the crankshaft speed changes are greater than an expected amount, the PCM interprets this as a misfire.
The PCM uses the Crankshaft Position sensor for misfire detection and to control spark and fueling. As the crankshaft rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 24X signal in combination with the Camshaft Position sensor 1X signal in order to accurately determine crankshaft position. The PCM also calculates a 4X signal from this information. The PCM uses the 4X signal for internal calculations. The
4X signal also provides a tach signal for any device which requires one.
Observe that as long as the PCM receives the Crankshaft Position sensor
24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.
DTC P0171 Fuel Trim System Lean Bank 1 Circuit Description
The powertrain control module (PCM) controls a Closed Loop air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The PCM monitors the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fuel trim values change in response to trends in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. You can use a scan tool in order to monitor the short and long term fuel trim. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the PCM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition. If the PCM detects an excessively Rich or Lean condition, the PCM sets a diagnostic trouble code (DTC). The long term fuel trim diagnostic parameter is an average of several of the long term speed load learn cells which the PCM selects based on the engine speed and the engine load.
DTC P0174 Fuel Trim System Lean Bank 2 Circuit Description
The powertrain control module (PCM) controls a Closed Loop air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The PCM monitors the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fuel trim values change in response to trends in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. You can use a scan tool in order to monitor the short and long term fuel trim. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the PCM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition. If the PCM detects an excessively Rich or Lean condition, the PCM sets a diagnostic trouble code (DTC). The long term fuel trim diagnostic parameter is an average of several of the long term speed load learn cells which the PCM selects based on the engine speed and the engine load.
KENG wrote: :: George wrote: ::: I have a 99 Silverado 4x4 with the 5.3l and automatic. A couple of ::: days ago I started it in the morning and it would rev up to almost ::: 2k then drop to about 500. I thought it was going to die out so I ::: tried to keep some light gas pedal to keep the rpm up a little. No ::: help at all. The engine would rev but wouldn't maintain a steady ::: idle. As it warmed up, the idle was ok and driveability wasn't a ::: problem. It set codes for the SES. I stopped at autozone and got ::: three codes. P0171, P0174, and P0300. What do I need to do for ::: further troubleshooting? It seems that there is a wide range of ::: what it might be. My truck has 4 o2 sensors. Surely they can't ::: all be bad in one try. Any ideas are appreciated. ::: ::: ::: :: :: :: :: DTC P0300 Engine Misfire Detected :: Circuit Description :: :: The Crankshaft Position sensor is mounted through the side of the :: engine block at the rear of Bank 2 above the starter assembly. The :: Crankshaft Position sensor works in conjunction with a 24X reluctor :: wheel on the crankshaft. The reluctor wheel is inside the engine :: immediately in front of the rear main bearing. The PCM provides a 12 :: volt power supply to the CKP sensor as well as a ground and a signal :: circuit. :: :: A misfire causes a change in crankshaft speed. The PCM 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 :: crankshaft speed has occurred. You can expect a certain amount of :: acceleration/deceleration between each firing stroke, but if the :: crankshaft speed changes are greater than an expected amount, the PCM :: interprets this as a misfire. :: :: The PCM uses the Crankshaft Position sensor for misfire detection :: and to control spark and fueling. As the crankshaft rotates, the :: reluctor wheel teeth interrupt a magnetic field produced by a magnet :: within the sensor. The sensors internal circuitry detects this and :: produces a signal which the PCM reads. The PCM uses this 24X signal :: in combination with the Camshaft Position sensor 1X signal in order :: to accurately determine crankshaft position. The PCM also calculates :: a 4X signal from this information. The PCM uses the 4X signal for :: internal calculations. The 4X signal also provides a tach signal for :: any device which requires one. :: :: Observe that as long as the PCM receives the Crankshaft Position :: sensor 24X signal, the engine will start. The PCM can determine top :: dead center for all cylinders by using the Crankshaft Position :: sensor 24X signal alone. The Camshaft Position sensor 1X signal is :: used by the PCM to determine if the cylinder at top dead center is :: on the firing stroke, or the exhaust stroke. The system attempts :: synchronization and looks for an increase in engine speed indicating :: the engine started. If the PCM does not detect an increase in engine :: speed, the PCM assumes it incorrectly synchronized to the exhaust :: stroke and re-syncs to the opposite cam position. A slightly longer :: cranking time may be a symptom of this condition. :: :: DTC P0171 Fuel Trim System Lean Bank 1 :: Circuit Description :: :: The powertrain control module (PCM) controls a Closed Loop air/fuel :: metering system in order to provide the best possible combination of :: driveability, fuel economy, and emission control. The PCM monitors :: the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel :: delivery based on the signal voltage while in Closed Loop. A change :: made to the fuel delivery changes the long and short term fuel trim :: values. The short term fuel trim values change rapidly in response :: to the HO2S signal voltages. These changes fine tune the engine :: fueling. The long term fuel trim values change in response to trends :: in the short term fuel trim. The long term fuel trim makes coarse :: adjustments to fueling in order to re-center and restore control to :: short term fuel trim. You can use a scan tool in order to monitor :: the short and long term fuel trim. The ideal fuel trim values are :: around 0 percent. A positive fuel trim value indicates that the PCM :: is adding fuel in order to compensate for a lean condition. A :: negative fuel trim value indicates that the PCM is reducing the :: amount of fuel in order to compensate for a rich condition. If the :: PCM detects an excessively Rich or Lean condition, the PCM sets a :: diagnostic trouble code (DTC). The long term fuel trim diagnostic :: parameter is an average of several of the long term speed load learn :: cells which the PCM selects based on the engine speed and the engine :: load. :: :: DTC P0174 Fuel Trim System Lean Bank 2 :: Circuit Description :: :: The powertrain control module (PCM) controls a Closed Loop air/fuel :: metering system in order to provide the best possible combination of :: driveability, fuel economy, and emission control. The PCM monitors :: the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel :: delivery based on the signal voltage while in Closed Loop. A change :: made to the fuel delivery changes the long and short term fuel trim :: values. The short term fuel trim values change rapidly in response :: to the HO2S signal voltages. These changes fine tune the engine :: fueling. The long term fuel trim values change in response to trends :: in the short term fuel trim. The long term fuel trim makes coarse :: adjustments to fueling in order to re-center and restore control to :: short term fuel trim. You can use a scan tool in order to monitor :: the short and long term fuel trim. The ideal fuel trim values are :: around 0 percent. A positive fuel trim value indicates that the PCM :: is adding fuel in order to compensate for a lean condition. A :: negative fuel trim value indicates that the PCM is reducing the :: amount of fuel in order to compensate for a rich condition. If the :: PCM detects an excessively Rich or Lean condition, the PCM sets a :: diagnostic trouble code (DTC). The long term fuel trim diagnostic :: parameter is an average of several of the long term speed load learn :: cells which the PCM selects based on the engine speed and the engine :: load. :: :: KenG
Thanks for the response. So, I have 3 DTC's but it doesn't appear to have any way to diagnose the trouble code. I'm still stuck for not knowing which part to throw at it. The autozone guy cleared the codes and it started ok this morning but there is probably still some fault in the system. I suppose I just have to wait for the code to be set again.
Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have fuel level DTCs also set. * A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis . * Excessive vibration from sources other than the engine could cause a misfire DTC. The following are possible sources of vibration: o Variable thickness brake rotor o Drive shaft not balanced o Certain rough road conditions * Observe, if more then one cylinder is mis-firing, the scan tool may only display one cylinder mis-firing. This will not be apparent until the repair is completed. Also, if an ignition coil/module ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders mis-firing. Inspect the ground circuit for the ignition coil/modules on the cylinder bank of the engine that has more then one cylinder mis-firing.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as you apply the water.
If the Misfire Current counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. Perform the diagnostic table for DTC P0335 first if this condition is suspected.
If a misfire is present and you suspect a fuel control problem, force the fuel system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.
A misfire may not be apparent at idle. The misfire may only occur above idle under a load. Road test the vehicle and monitor the misfire current counters.
If more than one cylinder is misfiring, the misfire current counters may only increment for only one cylinder. Example: Cylinders 1 and 8 are both misfiring, yet only cylinder 8 increments on the misfire current counter.
If one of the injector fuses is open, only two or three misfire current counters may increment for the corresponding side of the engine. 4.
The cylinder with the more significant misfire may cause another cylinders counter to increment only by a small amount. 10.
If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug. 12.
If there are no fuel system problems, refer to Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L,
6.0L. An engine mechanical problem can cause a spark plug to gas foul. Inspect for loose rockers, collapsed lifters or worn camshaft lobes.
If the customers concern is the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic. Refer to DTC P0420 Catalyst System Low Efficiency Bank 1 and/or DTC P0430 Catalyst System Low Efficiency Bank 2 .
DTC P0300 - Engine Misfire Detected
Step
Action
Value(s)
Yes
No
1
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
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