STS RWD V8-4.6L VIN A (2006)
Main Relay (Computer/Fuel System): Testing and Inspection
POWERTRAIN RELAY DIAGNOSIS
CIRCUIT DESCRIPTION
The main relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly
to the powertrain relay coil and the armature contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control
circuit, via an internal integrated circuit, called an output driver module. When the ECM commands the relay ON, the relay coil creates an
electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay
load circuit. The closing of the relay contacts allows current to flow from the battery to the following fuses and relays.
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V8 ECM fuse
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Post O2
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ODD coils fuse
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EVEN coils fuse
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Pre O2/CAM fuse
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S/P fan relay
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Low speed fan relay
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High speed fan relay
When the ignition switch is turned to the OFF position, power is interrupted to the output driver module in the ECM, and the powertrain relay
electromagnetic field collapses. This action allows the spring tension pulling on the armature to separate from the relay load circuit contact, which
interrupts current flow to the fuses and relays.
If the powertrain relay fails to close, the engine will crank, but will not run. The GMLAN and class II data communications will be available, with the
use of a CANdi module and scan tool.
DIAGNOSTIC AIDS
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The main relay will remain powered up for 15 seconds after the ignition switch is turned OFF.
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The powertrain relay system diagnosis table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Starting and
Charging. See: Starting and Charging/Testing and Inspection/Component Tests and General Diagnostics/Battery Inspection/Test
TEST
