| P1101 – Mass Air Flow Sensor Out of Self-Test Range
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Manufacturer Specific Definitions for P1101
Table of Contents
- What Does Code P1101 Mean?
- Where is the P1101 sensor located?
- What are the common causes of code P1101?
- Get Help with P1101
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
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