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Chevy: fault code po 144, 172, 175 (remedy)..Haynes..Manuel

Customer Question

fault code po 144, 172, 175 (remedy)?
1996 chevy 1500 I have the Haynes Repair Manuel
& know what the codes are.Just want possible remedy.   Thanks
Submitted: 4 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 4 years ago.

hi

there are a few things that could cause your engine to flood or run rich...

first,check the fuel pressure,make sure it don't have over 65psi,if it does,the problem may be the return line clogged also,a bad fuel pressure regulator may cause this..worst case,would be the spider injector

the problem may be the ect[engine coolant tempeture sensor]this is located on the front of the intake manifold...please print the info below

thanks

please ACCEPT my answer so I can get credit for my work.i don't receive commission unless you do ..I'm not always going to be giving you good news,so please don't let this stand in the way of you accepting my answer.it does not cost you more money.we will still be able to communicate.. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.PLEASE ASK IF YOU NEED MORE HELP

 

P0144

DTC P0144 HO2S Circuit High Voltage Bank 1 Sensor 3



Circuit Description

The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.

Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.

This diagnostic trouble code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the vehicle control module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:

 

  • An open or a short to voltage on either the HO2S signal or HO2S low circuits.
  • A malfunctioning HO2S.
  • A problem in the HO2S heater or its circuit.
  • A faulty HO2S ground.

This DTC is designed to detect an HO2S voltage that remains at a high (rich) voltage for more than 110 seconds during a 130 second test period. This DTC is set under the following conditions:

  • There is an HO2S circuit fault that results in a false rich exhaust condition.
  • The HO2S is correctly detecting the rich air/fuel ratio resulting from either a vacuum leak or a fuel control system problem.

Conditions for Running the DTC

  • No active TP sensor DTCs.
  • No active EVAP sensor DTCs.
  • No active IAT sensor DTCs.
  • No active MAP sensor DTCs.
  • No active ECT sensor DTCs.
  • No active MAF sensor DTCs.
  • No active misfire DTCs.
  • No intrusive tests (i.e., EGR or Catalyst) in progress.
  • No device control active.
  • The system voltage is more than 9 volts.

Rich Test Enable

  • System in closed loop.
  • The air/fuel ratio is between 14.5-14.8.
  • The throttle position is between 0-50 percent.
  • The above condition is met for 5 seconds.

Decel Fuel Cut-off (DFCO) Rich Test Enable

  • DFCO mode active.
  • System in closed loop.
  • The elapsed time since test enabled is more than 2 seconds.

Conditions for Setting the DTC

Rich Test

The O2 sensor voltage is more than 993 mV for more than 110 seconds.

DFCO Rich Test

The O2 sensor voltage is more than 468 mV for more than 40 seconds.

Action Taken When the DTC Sets

  • The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
  • The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.

Conditions for Clearing the MIL or DTC

  • The control module turns OFF the MIL afterXXXXXtrips when the test has run and passed.
  • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
  • Use a scan tool in order to clear the DTCs.

Diagnostic Aids

Important: Never solder HO2S wires.

Check the following items:

  • The fuel pressure: If the pressure is too high, the system will run rich. The VCM can compensate for some increase; however, if the pressure gets too high, the DTC may set.
  • A rich injector. Perform a Injector Balance Test.
  • A leaking injector.
  • Fuel contaminated oil.
  • EVAP canister purge: Check for a fuel saturation. If full of fuel, check the canister control and hoses.
  • Leaking fuel pressure regulator diaphragm by checking the vacuum line to the regulator for fuel.
  • The TP sensor: An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving.
  • False rich indication due to silicon contamination of the heated oxygen sensor. This DTC, accompanied by a lean driveability condition and a powdery white deposit on the sensor, may indicate a false rich indication.

An intermittent may be caused by any of the following conditions:

  • A poor connection.
  • Rubbed through wire insulation.
  • A broken wire inside the insulation.

Thoroughly check any circuitry that is suspected of causing the intermittent complaint.

Test Description

The number below refers to the step number on the diagnostic table.

  1. In order to determine if the engine is rich during De-acceleration Fuel Cut-Off (DFCO) operate the vehicle up to highway speed conditions and release the accelerator pedal allowing the vehicle to coast in gear. Monitor the scan tool HO2S voltage and the DFCO parameter. A rich condition will cause HO2S voltage to be above 468 mV during DFCO.
  1. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.
  2. This step checks the HO2S HIGH signal circuit for a short to voltage.
  1. An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.

 




DTC P0172 Fuel Trim System Rich Bank 1



Circuit Description

In order to provide the best possible combination of driveability, fuel economy, and emission control, the vehicle uses a closed loop air and fuel metering system. While in closed loop, the VCM monitors the oxygen sensor signal voltage. The VCM adjusts the fuel delivery based on a signal voltage. The long and short term fuel values, which a scan tool can monitor, indicate a change made to the fuel delivery. Ideal fuel trim values are around 0% (128 counts); if the oxygen sensor signal indicates a lean condition, the VCM will add fuel. This results in fuel trim values above 0%. If the oxygen sensor detects a rich condition, the fuel trim values will read below 0%. This will indicate that the VCM is reducing the amount of fuel delivered. The VCM sets this DTC when an excessively rich condition is detected.

Conditions for Running the DTC

 

  • No active O2 sensor DTCs.
  • No active TP sensor DTCs.
  • No active MAP sensor DTCs.
  • No active EGR sensor DTCs.
  • No active EVAP system sensor DTCs.
  • No active ECT sensor DTCs.
  • No active MAF sensor DTCs.
  • No active IAT sensor DTCs.
  • No active VS sensor DTCs.
  • No active misfire DTCs.
  • Throttle position less than 70%.
  • Engine speed is between 575 and 4,000 RPM.
  • The BARO greater than 70 kPa.
  • The ECT is between 75 and 114°C (167-237°F).
  • The MAP is between 22 and 85 kPa.
  • The IAT is between -8 and 76°C (46-169°F).
  • The MAF is between 3 and 85 g/s.
  • The vehicle speed less than 85 MPH.

Conditions for Setting the DTC

The average of the short term fuel trim values over a period of 120 seconds indicates that a rich condition is present.

Action Taken When the DTC Sets

Important: To complete a trip cycle for the fuel trim diagnostic, the fuel trim diagnostic test must enable and run according to the current DTC Will Set When criteria above. A trip is not considered complete until the fuel trim diagnostic has run by the VCM.

When the current DTC initially sets, a software flag indicating an emissions related fault sets for 3 trips. The flag will clear provided the lean condition is no longer present. However, if the VCM detects the conditions for setting the current DTC during a trip while the flag is still set, the VCM turns on the MIL (Malfunction Indicator Lamp). The MIL remains on during all of the subsequent trips until the DTC has been cleared by service or the lean condition has not been detected and the conditions for checking the fuel trim have been met for 3 consecutive trips.

Conditions for Clearing the MIL or DTC

  • The control module turns OFF the MIL afterXXXXXtrips when the test has run and passed.
  • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
  • Use a scan tool in order to clear the DTCs.

Diagnostic Aids

If using the diagnostic tables does not isolate the problem, try monitoring the LT fuel trim and fuel trim cell while operating the vehicle under various loads. This may isolate the condition which caused the setting of the current DTC.

A condition that causes the DTC P0300 Engine Misfire Detected may also set the current DTC; conversely an extremely rich condition which sets the current DTC can cause a misfire at idle and the DTC P0300 to set. If the cause of the current DTC cannot be determined and the DTC P0300 is also set, refer to DTC P0300.

Typical Fuel Trim Values



The fuel trim values table indicates the typical fuel adjustment values as displayed on a scan tool. Negative values, or a rich condition, indicates that the injector pulse width is being decreased in order to lean out the fuel mixture. Positive values, or a lean condition, indicates that the injector pulse width is being increased in order to richen the fuel mixture.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

 

  1. A more negative value indicates the VCM is leaning the fuel mixture (Rich condition), and a more positive value indicates the VCM is richening the fuel mixture (Lean condition).
  1. This step checks the fuel system for problems.

 






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