P1101 – Mass Air Flow Sensor Out of Self-Test Range

By Reinier (Contact Me)
Last Updated 2018-09-28
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P1101 HO2S11 Sensor Circuit Voltage Too Low Air Leak (AUDI, VOLKSWAGEN)
Airbag Control Module Signal Received (CHRYSLER, DODGE, JEEP)
Mass Air Flow Sensor Out of Self-Test Range (FORD, LINCOLN, MAZDA, MERCURY)
Manifold Absolute Pressure Sensor Abnormal (HYUNDAI)
Intake Air Flow System Performance (ISUZU)
Vacuum Control Solenoid Valve System Traction Control System (MITSUBISHI)
Neutral Position Switch Circuit High Input (SUBARU)

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What Does Code P1101 Mean?

OBD II fault code P1101 is a manufacturer specific code that is defined by carmakers Ford, Jaguar, Lincoln, Mazda, Mercedes, Mercury, and Oldsmobile as “MAF Sensor Out Of Self-Test Range”, and is set when the PCM (Powertrain Control Module) detects an abnormally high or low voltage from the MAF (Mass Airflow) sensor during the sensors’ self-test phase.

The purpose of a MAF sensor is to measure the total volume of air that enters the engine when the engine is running. The PCM uses this information as the basis from which to calculate an appropriate fuel delivery strategy to suit the current operating conditions, in order to maintain the air/fuel mixture within a narrow range on either side of the ideal 14.7 parts of air to one part of fuel mixture.

In practice, most MAF sensors use a heated element that is supplied with a 5-volt reference voltage. As air flows over the element the flowing air changes the elements’ resistance, and these changes are then relayed back to the PCM via a dedicated signal circuit. The PCM interprets the changes in the signal voltage as changing volumes of air, and it bases the injector pulse width on the volume of air that enters the engine at any given moment in order to maintain the air/fuel mixture.

As a practical matter though, the density of air is directly related to its temperature. Therefore, the PCM also uses input data from other engine sensors such as the engine coolant temperature sensor, intake air temperature sensor, the engine speed sensor, and in some cases, the barometric air pressure sensor to obtain a better idea of how much air actually enters the engine, as opposed to the desired volume of air.

However, for the PCM to be able to be sure that the input data from all implicated sensors correlate, it needs to be sure that the MAF sensor is calibrated correctly. To check this calibration, the PCM runs a test on the MAF sensor’s signal voltage; once when the ignition is switched on but with the engine not running, and once again when the engine is running at a predefined speed. In the first test on most applications, the signal voltage from the MAF sensor should be about 0.27 volts and the sensor fails the test when the signal voltage is significantly higher than this value.

During the second test, the MAF sensor should return a signal voltage of about 2.44 volts, with an allowable deviation of about 0.45 volts to either side of 2.44 volts. If this deviation is exceeded in any direction, the MAF sensor also fails the test. It should be noted however that the actual test voltages might vary somewhat between applications.

Nonetheless, when any or both self-tests fail, the PCM recognizes that it cannot control the injector pulse widths effectively (based on the volume of the intake air), and it will set code P1101, and illuminate a warning light as a result.

Why does code P1101 affect Ford, Jaguar, Lincoln, Mazda, Mercedes, Mercury, and Oldsmobile applications more than others?

On Ford applications, and especially F-series trucks, the most common cause of this code is air and/or engine vacuum leaks downstream of the MAF sensor that cause the MAF sensor to under report the air flow through the sensor during the second self-test.

On other applications, and especially Mercedes models, the most common cause of this code is oil contamination of the MAF sensor’s sensing element, which also causes the sensor to under report the air flow through the sensor.

Where is the P1101 sensor located?

The image above shows the typical location (circled) of the MAF sensor in the inlet tract. Note however that in many cases, the MAF sensor is a large, stubby tube that is inserted into the inlet ducting, and held in place with two clamps or spring-loaded clips. Note also that in most cases the MAF sensor is located closer to the throttle body than in the example shown here.

Nonetheless, MAF sensors are usually easy to identify, since they are usually the only sensors in the large diameter intake ducting.

What are the common causes of code P1101?

Some common causes of code P1101 could include the following-

  • Damaged, burnt, shorted, disconnected, or corroded wiring in the MAF sensors’ reference and/or signal circuit(s)
  • Oil contamination of the MAF sensors’ sensing element
  • Defective MAF sensor
  • Vacuum leaks downstream of the MAF sensor
  • Excessively dirty or clogged air filter element
  • The use of unsuitable aftermarket air filters
  • Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced

Other Manufacturer Specific Definitions for P1101

Mass Air Flow Sensor Out of Self-Test Range (Ford)
Intake airflow -incorrect (GM)
Heated oxygen sensor (HO2S) low voltage (Volkswagen)
Heated oxygen sensor (HO2S) 1, Bank 1 - low voltage/air leak (Audi)
Intake air flow -incorrect (Buick)
Intake airflow -incorrect (Cadillac)
Intake airflow -incorrect (Chevrolet)
Airbag Control Module Signal Received (Chrysler)
Ambient air temperature sensor -circuit high (Dodge)
Ambient air temperature sensor -circuit high (Freightliner)
Intake airflow -incorrect (Hummer)
Manifold Absolute Pressure Sensor Abnormal (Hyundai)
Mass air flow (MAF) and manifold absolute pressure (MAP) sensors – circuit malfunction (Isuzu)
Airbag Control Module Signal Received (Jeep)
Mass air flow (MAF) sensor/volume air flow   (VAF) sensor- range/performance problem (Land Rover)
Mass air flow (MAF) sensor -signal malfunction (Lincoln)
Mass air flow (MAF) sensor – out of self-test range (Mazda)
Mass air flow (MAF) sensor -signal malfunction (Mercury)
Traction control vacuum solenoid – circuit malfunction (Mitsubishi)
Intake air flow -incorrect (Pontiac)
Intake airflow – incorrect (Saab)
Intake air flow -incorrect (Saturn)
Park/neutral position (PNP) switch – circuit malfunction (Subaru)

BAT Team Discussions for P1101

  • need help with a subaru..plz
    I live in a small town and the Subaru dealer is an hour away. My 95 legacy check engine light came on and code is P1101. Neutral Position Circuit High Input? No one seems to know what this is or what it does. Should I be driving it..can anyone refer me to a link to buy one..I would appreciate any...
  • 98 subaru forester 2.5
    98 subaru forester 2.5 this car will not start when it is cold have lots of trouble it run fine after it gets warm the codes i am getting are p1100, p1101, p1120, p1121, is this the air control valve or the map sensor im getting codes for both does anyone know what could be the problem ...