Mechanics

MASS AIR FLOW SENSOR

2003 Dodge Neon

Engine Performance problem
2003 Dodge Neon 4 cyl Front Wheel Drive Automatic 64K miles

My computer Scanner shows P0171, which leads to the Mass Air Flow Sensor. Where is this sensor located, every parts store I call says MAP sensor which I thought was different. The car will shake or stall when in park, and get's really bad gas mileage now.
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T3jones
August 24, 2009.




DTC P0171: FUEL SYSTEM 1/1 LEAN

Monitored & Set Conditions
System is monitored with engine running in closed loop mode, ambient/battery temperature above 20 F (-7 C) and altitude less than 8500 feet, and fuel level greater than 15 percent. DTC will set if the PCM multiplies short term compensation by long term adaptive and a certain percentage is exceeded for two trips, a freeze frame is stored, the MIL illuminates and a DTC is stored.
Possible Causes
Good Trip Equal To Zero
Restricted Fuel Supply Line
Fuel Pump Inlet Strainer Plugged
Fuel Pump Module
O2 Sensor
O2 Signal Circuit
O2 Return Circuit
O2 Sensor Heater Operation
Throttle Position Sensor Sweep
MAP Sensor Operation
ECT Sensor Operation
Engine Mechanical Problem
Fuel Contamination/Exhaust Leak
Testing
WARNING: Fuel system is under constant pressure even when ignition is off. Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released.

NOTE: Before proceeding, check for contaminants that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil and coolant.

NOTE: Diagnose any Misfire DTC(s) first, if set along with the fuel system DTC.

Ignition on, engine not running. With the DRBIII(R) scan tool, read DTCs and record the related freeze frame data. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, see INTERMITTENT CONDITION under SELF-DIAGNOSTICS SYSTEM.
WARNING: Fuel system is under constant pressure even when ignition is off. Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE.

Install a fuel pressure gauge. Ignition on, engine not running. With the DRBIII(R) scan tool, actuate ASD fuel system test and observe fuel pressure gauge. Fuel pressure should be 53-63 psi (365-434 kPa). Turn ignition off. If fuel pressure is within specification, stop all actuations and go to next step. If fuel pressure is less than specification, stop all actuations and go to step 12.
NOTE: If one of the O2 sensors signal or return circuits are shorted to ground or voltage, all the other O2 sensor voltage readings will be affected. After the repairs have been made, verify proper O2 sensor operation. If all the O2 sensor voltage readings have not returned to normal, follow the diagnostic procedure for the remaining O2 sensors.

Start the engine. Allow the engine to reach normal operating temperature. With the DRBIII(R) scan tool, read the O2 sensor voltage. Is the voltage switching between 2.5-3.4 volts? If yes, go to next step. If no, go to step 9.
Turn the ignition off. Allow the O2 sensor to cool down before continuing the test. Allow the O2 sensor voltage to stabilize at 5.0 volts. Ignition on, engine not running. With the DRBIII(R) scan tool, actuate the O2 heater test. With the DRBIII(R) scan tool, monitor O2 sensor voltage for at least 2 minutes. Does the voltage stay above 4.5 volts? If yes, replace the O2 sensor. If no, go to next step.
Ignition on, engine not running. With the DRBIII(R) scan tool, read TP sensor voltage. While monitoring the DRBIII(R) scan tool, slowly open and close the throttle. Does the voltage increase and decease smoothly? If yes, go to next step. If no, replace the TP sensor.
Turn the ignition off. Connect a vacuum gauge to a manifold vacuum source. Start the engine. Allow the engine to idle. If engine will not idle, maintain a constant RPM above idle. With the DRBIII(R) scan tool in sensors, read the MAP sensor vacuum value. Is the DRBIII(R) scan tool reading within 1 in. Hg of the vacuum gauge reading? If yes, go to next step. If no, replace the MAP sensor.
For this test to be valid, the thermostat must be operating correctly. This test works best if performed on a cold engine (cold soak). Ignition on, engine not running. With the DRBIII(R) scan tool, read the Engine Coolant Temperature (ECT) sensor value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature. If engine coolant temperature is above 180 F (82 C), allow the engine to cool until 150 F (65 C) is reached. Start the engine. During engine warm-up, monitor the ECT sensor value. The temperature value change should be a smooth transition from start up to normal operating temperature 180 F (82 C). The value should reach at least 180 F (82 C). Did the ECT value increase a smooth transition and did it reach at least 180 F (82 C)? If yes, go to next step. If no, replace the ECT sensor.
Check for any of the following conditions/mechanical problems: Ensure air intake system is free from leaks.
Ensure engine vacuum is at least 13 in. Hg at idle in Park or Neutral.
Ensure valve timing is correct.
Ensure engine compression is within specification.
Ensure exhaust system is free from restrictions or leaks.
Ensure PCV system flows freely.
Ensure torque converter stall speed is within specification.
Ensure power brake booster has no internal vacuum leaks.
Ensure fuel is not contaminated.
Ensure fuel injectors are not restricted.
Ensure fuel injector harness connectors are connected to correct fuel injectors.
Are there any engine mechanical problems? If yes, repair as necessary. If no, test is complete.
Ignition on, engine not running. Disconnect the O2 sensor harness connector. With the DRBIII(R) scan tool, monitor the O2 sensor voltage. The O2 sensor voltage should read 5.0 volts on the DRBIII(R) scan tool with the connector disconnected. Using a jumper wire, jump across the O2 sensor harness connector from the O2 signal circuit to the O2 return circuit at the O2 sensor harness connector. The voltage should drop from 5.0 volts to 2.5 volts with the jumper wire in place. Did the O2 sensor volts change from 5.0 volts to 2.5 volts? If yes, replace the O2 sensor. If no, go to next step.
Turn the ignition off. Disconnect the O2 sensor harness connector. Ignition on, engine not running. With the DRBIII(R) scan tool, monitor the O2 sensor voltage. Is the voltage above 4.8 volts? If yes, go to next step. If no, check the O2 signal circuit for a short to ground, open, or short to voltage. Inspect the O2 sensor connector and the PCM harness connector. If OK, replace and program the PCM. See PROGRAMMING.
Turn the ignition off. Disconnect the O2 sensor harness connector. Ignition on, engine not running. Measure the voltage on the O2 return circuit in the O2 sensor harness connector. Is the voltage at 2.5 volts? If yes, check the fuel system for contaminates. Also, check the exhaust system for any leaks. If no, check the O2 return circuit for a short to ground, open, or short to voltage. Inspect the O2 sensor connector and the PCM harness connector. If OK, replace and program the PCM. See PROGRAMMING.
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released.

Turn the ignition off. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE. Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module. Install special 5/16" Fuel Line Adapter (6539) between disconnected fuel line and the fuel pump module. Attach a fuel pressure test gauge to the " T" fitting on fuel line adapter. Turn the ignition on. With the DRBIII(R) scan tool, actuate the ASD fuel system test and observe the fuel pressure gauge. Note fuel pressure reading, stop ASD fuel system test and turn ignition off. If fuel pressure is 53-63 psi (365-434 kPa), repair or replace fuel supply line as necessary. If fuel pressure is not 53-63 psi (365-434 kPa), go to next step.
Release fuel pressure. Remove fuel pump module from fuel tank. Inspect fuel inlet strainer. Is the fuel inlet strainer plugged? If yes, replace fuel inlet strainer. If no, go to next step.
There are no possible causes remaining, replace the fuel pump module.

BMRFIXIT
Aug 24, 2009.


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