RAM 1500 Van V8-5.9L VIN Z LDC (2001)
Ignition Relay: Description and Operation
IGNITION CONTROL
The ignition Systems used on the 3.9L V-6, the 5.2L V-8 and the 5.9L V-8 are basically identical.
The ignition system is controlled by the Powertrain Control Module (PCM) on all engines.
The ignition system consists of:
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Spark Plugs
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Ignition Coil
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Secondary Ignition Cables
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Distributor (contains rotor and camshaft position sensor)
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Powertrain Control Module (PCM)
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Crankshaft Position, Camshaft Position, Throttle Position and MAP Sensors
AUTO SHUT DOWN RELAY
PCM Output
The 5-pin, 12-volt, Automatic Shutdown (ASD) relay is located in the Power Distribution Center (PDC). Refer to label on PDC cover for relay
location.
The ASD relay supplies battery voltage (12+ volts) to the fuel injectors and ignition coil(s). With certain emissions packages it also supplies
12-volts to the oxygen sensor heating elements.
The ground circuit for the coil within the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the ASD relay by
switching its ground circuit ON and OFF.
The ASD relay will be shut-down, meaning the 12-volt power supply to the ASD relay will be de-activated by the PCM if:
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the ignition key is left in the ON position. This is if the engine has not been running for approximately 1.8 seconds.
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there is a crankshaft position sensor signal to the PCM that is lower than pre-determined values.
ASD Sense - PCM Input
A 12 volt signal at this input indicates to the PCM that the ASD has been activated. The relay is used to connect the oxygen sensor heater element,
ignition coil and fuel injectors to 12 volt + power supply.
This input is used only to sense that the ASD relay is energized. If the Powertrain Control Module (PCM) does not see 12 volts at this input when
the ASD should be activated, it will set a Diagnostic Trouble Code (DTC).
CAMSHAFT POSITION SENSOR
The Camshaft Position (CMP) sensor is located in the distributor.
The sensor contains a hall effect device called a sync signal generator to generate a fuel sync signal. This sync signal generator detects a rotating
pulse ring (shutter) on the distributor shaft. The pulse ring rotates 180 degrees through the sync signal generator. Its signal is used in conjunction
with the Crankshaft Position (CKP) sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors
with their respective cylinders.
When the leading edge of the pulse ring (shutter) enters the sync signal generator, the following occurs: The interruption of magnetic field causes
the voltage to switch high resulting in a sync signal of approximately 5 volts.
When the trailing edge of the pulse ring (shutter) leaves the sync signal generator, the following occurs: The change of the magnetic field causes
the sync signal voltage to switch low to 0 volts.
