Ignition System Overview
The electronic ignition system controls fuel combustion by providing
a spark in order to ignite the compressed air/fuel mixture at the correct
time. In order to provide optimum engine performance, fuel economy,
and control of exhaust emissions, the PCM controls the spark advance
of the ignition system. The electronic ignition system has the following
advantages over a mechanical distributor system:
| • | Remote mounting capability |
| • | No mechanical load on the engine |
| • | More coil cool down time between firing events |
| • | Elimination of mechanical timing adjustments |
| • | Increased available ignition coil saturation time |
The electronic ignition system does not use the conventional
distributor and coil. The ignition system consists of the following components/circuits:
| • | Eight ignition coils/modules |
| • | Eight ignition control (IC) circuits |
| • | The camshaft position (CMP) sensor |
| • | The 1X camshaft reluctor wheel |
| • | The crankshaft position (CKP) sensor |
| • | The 24X crankshaft reluctor wheel |
| • | The related connecting wires |
| • | The powertrain control module (PCM) |
Crankshaft Position Sensor and Reluctor Wheel
The crankshaft position (CKP) sensor is located in the right rear of
the engine, behind the starter. The CKP sensor is a dual magneto resistive
type sensor. The dual micro switches monitor both notches of the reluctor
wheel for greater accuracy. The CKP sensor works in-conjunction with
a 24X reluctor wheel. The reluctor wheel is mounted on the rear of
the crankshaft. The 24X reluctor wheel uses 2 different width
notches that are 15 degrees apart. This pulse width encoded (PWE) pattern
allows cylinder position identification within 90 degrees of
crankshaft rotation. In some cases, cylinder identification can be located
in 45 degrees of crankshaft rotation. This reluctor wheel also
has dual track notches that are 180 degrees out of phase. The
dual track design allows for quicker starts and accuracy.
The PCM also receives a 4X signal from the CKP sensor. The PCM utilizes
the 4X signal for the following conditions:
The CKP signal must be available for the engine to start. The CMP signal
is not needed in order to start and operate the engine. The PCM can determine
when a particular cylinder is on either a firing or exhaust stroke
by the 24X signal. The CMP sensor is to determine what stroke the
engine is on. The system will attempt synchronization and look for
an increase in the MAF signal. An increase in the MAF signal indicates
the engine has started. If the PCM does not detect an increase in
the MAF signal, a re-sync will occur to the opposite cam position.
A slightly longer cranking time may be a symptom of this condition.
Camshaft Position Sensor
The camshaft position (CMP) sensor is mounted through the top of the
engine block at the rear of the valley cover. The CMP sensor works
in conjunction with a 1X reluctor wheel. The reluctor wheel is located
at the rear of the camshaft. The CMP sensor is used to determine whether
a cylinder is on the firing or the exhaust stroke. As the camshaft
rotates, the reluctor wheel interrupts a magnetic field produced by
a magnet within the sensor. The CMP sensor internal circuitry detects
this and produces a signal which is used by the PCM. The PCM uses
this signal in combination with the CKP 24X signal to determine crankshaft
position and stroke.
The CKP signal must be available for the engine to start. The CMP signal
is not needed to start and operate the engine. The PCM can determine when
a particular cylinder is on either a firing or exhaust stroke by the
24X signal. The CMP sensor is to determine what stroke the engine
is on. The system will attempt synchronization and look for an increase
in the MAF signal. An increase in the MAF signal indicates that the
engine has started. If the PCM does not detect an increase in the
MAF signal, a re-sync will occur to the opposite cam position. A slightly
longer cranking time may be a symptom of this condition.
Ignition Coils/Module
The ignition system on this vehicle features a multiple coil ignition
and is known as coil near plug. The secondary ignition wires are short
compared with a distributor ignition system wire. The 8 ignition
coils/modules are individually mounted above each cylinder on the
rocker covers. The coils/modules are fired sequentially. There is
an ignition control (IC) circuit for each ignition coil/module. The
8 ignition control circuits are connected to the PCM. All timing
decisions are made by the PCM, which triggers each coil/module individually.
The ignition coil/modules are supplied with the following circuits:
| • | The ignition feed circuit |
| • | The ignition control circuit |
| • | The reference low circuit |
The ignition feed circuits are fused separately for each bank of the
engine. The 2 fuses also supply the injectors for that bank of the
engine. Each coil/module is serviced separately.
This system puts out very high ignition energy for plug firing. Because
the ignition wires are shorter, less energy is lost to ignition wire resistance.
Since the firing is sequential, each coil has 7 events to saturate
as opposed to the 3 events in a waste spark arrangement. Futhermore,
no energy is lost to the resistance of a waste spark system.
Circuits Affecting Ignition Control
In order to properly control the ignition timing, the PCM relies on
the following information:
| • | The engine load (manifold pressure or vacuum) |
| • | The atmospheric (barometric) pressure |
| • | The intake air temperature |
| • | The crankshaft position |
The ignition control (IC) system consists of the following components:
| • | The ignition coil/modules |
| • | The 24X crankshaft position sensor |
| • | The powertrain control module (PCM) |
The ignition control utilizes the following in order to control the
spark timing functions:
| • | The 24X signal -- The 24X crankshaft position sensor sends
a signal to the PCM. The PCM uses this signal in order to determine the crankshaft
position. The PCM also utilizes this signal in order to trigger the
fuel injectors. |
| • | The ignition control (IC) circuits -- The PCM uses these
circuits in order to trigger the ignition coil/modules. The PCM uses the crankshaft
reference signal in order to calculate the amount of spark advance
needed. |
Noteworthy Ignition Information
There are important considerations to point out when servicing the ignition
system. The following noteworthy information will list some of these, to help
the technician in servicing the ignition system.
| • | The ignition coils secondary voltage output capabilities are very
high -- more than 40,000 volts. Avoid body contact with ignition
high voltage secondary components when the engine is running, or personal
injury may result. |
| • | The 24X crankshaft position sensor is the most critical part of
the ignition system. If the sensor is damaged so that pulses are not generated,
the engine will not start. |
| • | Crankshaft position sensor clearance is very important! The sensor
must not contact the rotating interrupter ring at any time, or sensor damage
will result. If the interrupter ring is bent, the interrupter ring
blades will destroy the sensor. |
| • | Ignition timing is not adjustable. There are no timing marks on
the crankshaft balancer or timing chain cover. |
| | Important: Never pierce a secondary ignition wire or boot for any testing purposes.
|
| • | Be careful not to damage the secondary ignition wires or boots when
servicing the ignition system. Rotate each boot in order to dislodge the boot
from the plug or from the coil tower before pulling the boot from either
a spark plug or the ignition coil. Future problems are guaranteed
if pinpoints or test lights are pushed through the insulation for testing. |
Powertrain Control Module (PCM)
The PCM is responsible for maintaining proper spark and fuel injection
timing for all driving conditions. In order to provide optimum driveability
and emissions, the PCM monitors input signals from the following components
in calculating ignition control (IC) spark timing:
| • | The engine coolant temperature (ECT) sensor |
| • | The intake air temperature (IAT) sensor |
| • | The mass air flow (MAF) sensor |
| • | The trans range inputs from transaxle range switch |
| • | The throttle position (TP) sensor |
| • | The vehicle speed sensor (VSS) |
Results of Incorrect Operation
An ignition control circuit that is open, grounded, or short to voltage
will set an ignition control circuit DTC. If a fault occurs in the IC output
circuit when the engine is running, the engine will experience a misfire.
DTCs P0351-P0358 will set when a malfunction is detected with
an ignition control circuit. When an ignition control DTC sets, the
PCM will disable the injector for the appropriate cylinder.
The PCM uses information from the engine coolant temperature sensor
in addition to the RPM in order to calculate spark advance values as follows:
| • | High RPM equals more advance |
| • | A cold engine equals more advance |
| • | Low RPM equals less advance |
| • | A hot engine equals less advance |
Therefore, detonation may be caused by high resistance in the engine
coolant temperature sensor circuit. Poor performance may be caused by low
resistance in the engine coolant temperature sensor circuit.
If the engine cranks but will not run, or immediately stalls,
the Engine Cranks But Will Not Run diagnostic table must be used to determine
if the failure is in the ignition system or the fuel system. If DTC
P0300, P0341, P0342, P0343, P0335, or P0336 is set, the appropriate
diagnostic trouble code table must be used for diagnosis.
