Error Code P1101 is defined as Mass Airflow Sensor Out of Self-Test Range. This means the Mass Airflow System is experiencing an issue like due to faulty sensor, air leak or bad connectors.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, particularly those vehicles made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs of course vary from one make and/or model to another.


Error Code P1101 takes place when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) detects a fault or discrepancy within the MAF (Mass Air Flow) sensor system, as the PCM conducts its self-diagnosis called KOER or Key On Engine Running. If the voltage from the MAF is greater or lesser than the manufacturer allowed, the test fails.

Other related codes include P1001, P1100, P1102, P1103, P1104, and P1105 code.

Common Symptoms

As with other error codes, P1101 triggers the Check Engine light on the dashboard and store the code. Other common symptoms include drivability issues that cause poor engine performance, such as:

  • Rough idling
  • Erratic startup
  • Reduced engine power while running
  • Increase in fuel consumption

Possible Causes

There are many possible causes for this code to appear, some of the most common causes include:

  • Faulty MAF sensor
  • Faulty connectors or wirings in the MAF harness
  • Poor electrical connection in MAF sensor
  • Air leaks before or after the MAF sensor

How to Check

As with other error codes, diagnosis for Error Code P1101 requires the use of OBD-II scanner and a DVOM (digital volt/ohm meter). The steps include:

  • Visual inspection of the wirings and connectors of the MAF sensor harness; the technician should check all the connectors, wirings and other components associated with the MAF system
  • Them, the technician check the air filter for debris to make sure there are no obstructed flow of air
  • Then, after making the necessary repairs or replacements, the technician will clear the codes and test the system to see if the code comes back
  • If the code returns, the mechanic will download the freeze frame data of the PCM, along with other stored codes
  • The technician will also remove the MAF sensor carefully, to see if it’s dirty
  • Next, he will conduct a smoke test to check for leaks before and after the MAF sensor within the vacuum system
  • If there are no leaks detected after fixing the found leaks, the code will then be cleared again. They will then use the DVOM to test the MAF sensor for the reference voltage and ground.
  • If no voltage or ground signal has been detected, they will disconnect the PCM and all related control modules, check the continuity within the battery ground
  • The technician will then check for the continuity between the PCM and the MAF sensor, along with the continuity between the various control modules and the PCM
  • Lastly, he will clear the codes again and retest the system to see if the code comes back

How to Fix

Repairs for this error code are as easy as its diagnosis, and as with other codes, a thorough diagnosis is needed for a complete repair.

  • Repair or replacement of faulty, damaged, or loose connectors, wirings or other components within the MAF sensor harness
  • Cleaning or replacement of dirty air filter
  • Cleaning the MAF sensor using specialized cleaner. Allow the sensor to dry before replacing.
  • Repair leaks within the vacuum system
  • Replacement of the MAF sensor if it still doesn’t work after cleaning
  • Replace faulty control module, such as PCM, if have been tested to be “bad”. Note that replacing the PCM will require reprogramming by the mechanic

One of the most common mistakes when diagnosing this error code is replacing the MAF sensor without trying to clean it first. In many cases, cleaning can solve the P1101 code. Also, it pays to check for vacuum leaks, as these kinds of problems are what lead to the persistence of the code.

Error Code P1101 may not cause major operation problems for the vehicle, but depending on the nature and severity of the problem, it can cause rough driving, power loss and increase in fuel consumption. Also, if left unaddressed for a long time, it can cause serious internal problems for the engine. Thus, it is important to have this error code fixed as soon as possible.