GM Century/Lumina/Grand Prix/Intrigue 1997-2000

Mass Air Flow (MAF) Sensor

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OPERATION



The Mass Air Flow (MAF) sensor measures the amount of air which passes through it into the engine during a given time. The PCM uses the mass air flow information to monitor engine operating conditions for fuel delivery calculations. A large quantity of air indicates acceleration, while a small quantity of air indicates deceleration or idle.



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Fig. Typical MAF sensor location-3.4L (VIN X) engine shown, others similar



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Fig. MAF sensor location-3.8L engines

The MAF sensor produces a frequency signal which can be monitored using a scan tool. The frequency will vary within a range around 2000 Hz at idle to about 10,000 Hz at maximum engine load.

A technician's scan tool reads the MAF value and displays it in grams per second (gm/s). At idle, it should read between 4 gm/s-7gm/s on a fully warmed up engine. Values should change rather quickly on acceleration but values should remain fairly stable at any given RPM. A failure in the MAF sensor circuit should set a Diagnostic Trouble Code (DTC).

TESTING



As with most all engine control sensors used in your vehicle, a thorough and proper test can only be performed by a qualified technician using a scan tool to read the data stream from the PCM. There are a few items you should check before taking the vehicle to a qualified technician for diagnosis and repair.



Look for a skewed or stuck Throttle Position (TP) sensor. A malfunctioning TP sensor or TP circuit can cause the PCM to incorrectly calculate the predicted mass air flow value. A scan tool is required to check the Throttle Angle but you can still check for a sticking throttle plate from excessive deposit build up on the throttle plate or in the throttle bore. A poor TP sensor connection, the TP signal circuit shorted to ground or high resistance in the TP sensor ground circuit are also problem areas to check.
 
Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections.
 
Look for a misrouted or damaged harness or damaged wiring going to the IAT sensor, especially if heavy work has recently been done where the connector could have been damaged.
 
Check the MAF sensor harness to make sure it is not routed too close to high voltage wires such as spark plug leads.
 
Check for a plugged intake duct or dirty air filter element.
 
Check for a skewed or unresponsive MAP sensor. The barometric pressure used to calculate the default Mass Air Flow value is based on the MAP sensor reading. A skewed MAP sensor at key ON will cause the BARO reading to be incorrectly calculated. Also, with the engine running, an unresponsive MAP sensor (due to poor vacuum connections, damaged vacuum source, defective vacuum hoses, unmetered air getting into the intake manifold) will cause inaccurate BARO reading updates during wide-open throttle conditions. Both of these conditions result in a difference between the actual MAF sensor signal and the predicted MAF value (PCM calculated). If a large difference between these two values occurs, a DTC will be set. This condition may also cause abnormal IAC counts and hard starts.
 


NOTE
If there is a failure on the MAF sensor circuit, A DTC will set. Refer to Trouble Codes in this section.



Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
 
With the engine running, lightly tap on the MAF sensor and wiggle the wires at the connector, while watching for a change in idle speed. A common problem is MAF sensor wire damage.
 

REMOVAL & INSTALLATION




NOTE
The MAF sensor is located on the air intake housing. Most MAF sensors have a fine mesh screen in front. Use care not to damage the screen when working around the MAF sensor and/or the air intake ducting. Do not allow the sensing elements to touch anything (including solvents and lubricant). Do not drop or handle roughly the MAF sensor. A damaged screen could restrict airflow and lead to a driveability problem.

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connector.
  4.  
  5. Remove the air inlet duct from the MAF sensor and remove the MAF from the air intake duct.
  6.  

To install:

  1. Installation is the reverse of removal.
  2.  
  3. Note that the MAF sensor may have an air flow direction arrow (usually located on top of the MAF sensor). The MAF sensor must be mounted with the arrow pointing towards the throttle body.
  4.  
  5. Take care to ensure that the MAF sensor locating tabs and the locating slots of the intake air ducts line up before connecting the MAF sensor and the intake air ducts.
  6.  
  7. Make sure the MAF sensor is seated in the air inlet grommet and that the electrical connection is secure.
  8.  

 
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