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type H: negative (-) multiplex
The system is most commonly found in 1999 and newer Grand Am and Alero models, in 2000 and
newer Impala and Monte Carlo models, and in Chrysler and Mazda models. The door lock switch or
door key cylinder may contain either one or two resistors.
Single-Resistor Type
If one resistor is used in the door lock switch/key cylinder, the wire will pulse ground in one direction
and resistance to ground when operated in the opposite direction.
Two-Resistor Type
If two resistors are used in the factory door lock switch/key cylinder, the door lock switch/key cylinder
will read resistance to ground in both directions.
Determining the Proper Resistor Values
To determine the resistor values, the door lock switch/key cylinder must be isolated from the factory
door lock system. For testing, use a calibrated digital multimeter that is set to ohms.
I I M M P P O O R R T T A A N N T T ! ! To ensure an accurate resistance reading, do not touch the resistor or leads
during testing.
1.
Cut the output wire from the door lock switch/key cylinder in half.
2.
Test with the meter from the switch side of the cut door lock switch/key cylinder wire to a reliable
ground source. Some good ground references are the ground input source to the door lock
switch/key cylinder or battery ground.
3.
Operate the door lock switch/key cylinder in both directions to determine the resistor values. If
the multimeter displays zero resistance in one direction, no resistor is needed for that direction.
4.
Once the resistor value(s) is determined, refer to the wiring diagram for proper wiring.
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