Alero V6-3.4L VIN E (1999)
Mass Air Flow (MAF) Sensor: Diagnostic Aids
Basic Knowledge Required
Without a basic knowledge of electricity, it will be difficult to use the diagnostic procedures contained in this section. You should understand the basic
theory of electricity and know the meaning of voltage (volts), current (amps) and resistance (ohms). You should understand what happens in a circuit
with an open or a shorted wire. You should be able to read and understand a wiring diagram.
Checking Aftermarket Accessories
Do not connect aftermarket accessories into the following circuits:
CAUTION: Refer to SIR Service Precautions Caution in Cautions and Notices.
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SIR circuits, all such circuits are indicated on circuit diagrams with the SIR symbol.
NOTE: Refer to OBD II Symbol Description Notice in Cautions and Notices.
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OBD II circuits, all such circuits are indicated on circuit diagrams with the OBD II symbol.
Always check for aftermarket accessories (non-OEM) as the first step in diagnosing electrical problems. If the vehicle is so equipped, disconnect the
system to verify that these add-on accessories are not the cause of the problems.
Possible causes of vehicle problems related to aftermarket accessories include:
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Power feeds connected to points other than the battery.
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Antenna location.
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Transceiver wiring located too close to vehicle electronic modules or wiring.
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Poor shielding or poor connectors on antenna feed line.
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Check for recent service bulletins detailing installation guidelines for aftermarket accessories.
Intermittents and Poor Connections Diagnosis
Most intermittents are caused by faulty electrical connections or wiring. Inspect for the following items:
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Wiring broken inside the insulation.
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Poor connection between the male and female terminal at a connector. Refer to Testing for Proper Terminal Contact below for the specific
procedure.
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Poor terminal to wire connection. Some conditions which fall under this description are poor crimps, poor solder joints, crimping over wire the
insulation rather than the wire itself and corrosion in the wire to terminal contact area, etc.
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Wire insulation which is rubbed through. This causes an intermittent short as the bare area touches other wiring or parts of the vehicle.
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Refer to Testing for Electrical Intermittents for test procedures to detect intermittent open, high resistance, short to ground, and short to voltage
conditions. See: General Electrical Diagnostic Procedures/Troubleshooting Tests/Testing For Proper Terminal Contact
General Information
The following is an example of a symptom and the correct course of action taken by the technician.
IMPORTANT: Research for possible bulletins, DTCs and the vehicle's service history. Also, thoroughly screen the customer regarding the problem in
order to complete the repair of the vehicle and completely satisfy the customer when a DTC or a symptom diagnosis is not available.
Verify the Customer Concern, Check the Problem
Customer complaint is the headlamps are inoperative. Verify the normal operating procedure of the circuit and the components that share that circuit.
Review the Headlamps Electrical Schematic (Preliminary Checks)
Review the schematic, it is essential to understand how a circuit should work before trying to figure out why it doesn't. After understanding how a circuit
should operate, read the schematic again, this time keeping in mind what has been learned by operating the circuit. Since both the low beam headlamps
are inoperative, ensure that the following components are operating properly.
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The headlamp Switch.
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The YEL wire.
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Low contacts of the Headlamp Dimmer Switch.
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C100 terminal 1E.
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The TAN wires. Grounds G105 and G109.
Perform the System Check
The system check indicates that the low beam headlamps operate when the high beam switch is in high. Also, the high beam indicator illuminates but
neither high beam headlamp operates.
Check For Bulletins
Utilizing a combination of Techline tools and the information accumulated from the Preliminary Checks, check for bulletins.
Isolate the Root Cause
At this point analyze and (diagnose the problem), and develop text. Since the high beam indicator illuminated when the headlamp dimmer switch was in
the high position, the high contacts of the headlamp dimmer switch and the LT GRN wire between the headlamp dimmer switch and C100 are good. At
this point, it is extremely unlikely that the high beam filaments in the RH and LH headlamps are both open or that both headlamp connections are bad.
The cause must be a bad connection at C100 or an open in the LT GRN wire between C100 and the RH headlamp.