For 1990-2009 cars

The electronic ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide optimum engine performance, fuel economy, and control of exhaust emissions, the PCM controls the spark advance of the ignition system. Electronic ignition has the following advantages over a mechanical distributor system:

• | No moving parts.

• | Less maintenance.

• | 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 three ignition coils, an ignition control module, a camshaft position sensor, 2 Hall-effect crankshaft position sensors, an engine crankshaft balancer with interrupter rings attached to the rear, related connecting wires, and the Ignition Control (IC) and fuel metering portion of the PCM.

Conventional ignition coils have one end of the secondary winding connected to the engine ground. In this ignition system, neither end of the secondary winding is grounded. Instead, each end of a coil's secondary winding is attached to a spark plug. Each cylinder is paired with the cylinder that is opposite it (1-4, 2-5, 3-6). These two plugs are on companion cylinders, i.e., on top dead center at the same time.

When the coil discharges, both plugs fire at the same time to complete the series circuit. The cylinder on compression is said to be the event cylinder and the one on exhaust is the waste cylinder. The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverse roles. This method of ignition is called a waste spark ignition system.

Since the polarity of the ignition coil primary and secondary windings is fixed, one spark plug always fires with normal polarity and its companion plug fires with reverse polarity. This differs from a conventional ignition system that fires all the plugs with the same polarity. Because the ignition coil requires approximately 30% more voltage to fire a spark plug with reverse polarity, the ignition coil design is improved, with saturation time and primary current flow increased. This redesign of the system allows higher secondary voltage to be available from the ignition coils - greater than 40 kilovolts (40,000 volts) at any engine RPM. The voltage required by each spark plug is determined by the polarity and the cylinder pressure. The cylinder on compression requires more voltage to fire the spark plug than the one on exhaust.

It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its companion plug. The disconnected plug wire acts as one plate of a capacitor, with the engine being the other plate. These two capacitor plates are charged as a spark jumps across the gap of the connected spark plug. The plates are then discharged as the secondary energy is dissipated in an oscillating current across the gap of the spark plug that is still connected. Secondary voltage requirements are very high with an open spark plug or spark plug wire. The ignition coil has enough reserve energy to fire the plug that is still connected at idle, but the coil may not fire the spark plug under high engine load. A more noticeable misfire may be evident under load; both spark plugs may then be misfiring.

### 24X and 7x Crankshaft Position Sensors/Harmonic Balancer Interrupter Ring

The 24X crankshaft position sensor (1), secured in an aluminum mounting bracket (3) and bolted to the front side of the engine timing chain cover (2), is partially behind the crankshaft balancer (refer to the 24X Crankshaft Position Sensor graphic).

The 7x crankshaft position sensor uses a two wire connector at the sensor and a three-way connector at the ignition control module.

The 24X crankshaft position sensor contains a Hall-effect switch. The magnet and Hall-effect switch are separated by an air gap. A Hall-effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (called an interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON-OFF-ON-OFF-ON-OFF. Compared to a conventional mechanical distributor, this ON-OFF signal is similar to the signal that a set of breaker points in the distributor would generate as the distributor shaft turned and the points opened and closed.

In the case of the electronic ignition system, the piece of steel is a concentric interrupter ring mounted to the rear of the crankshaft balancer. The interrupter ring has blades and windows that, with crankshaft rotation, either block the magnetic field or allow it to reach the Hall-effect switch. The Hall-effect switch is called a 24X crankshaft position sensor, because the interrupter ring has 24 evenly spaced blades and windows. The 24X crankshaft position sensor produces 24 ON-OFF pulses per crankshaft revolution.

The 7x crankshaft position sensor is the other Hall-effect switch closer to the crankshaft. The interrupter ring is a special wheel cast on the crankshaft that hes seven machined slots, six of which are equally spaced 60 degrees apart. The seventh slot is spaced 10 degrees from one of the other slots. as the interrupter ring rotates with the crankshaft, the slots change the magnetic field. this will cause the 7x the Hall-effect switch to ground the 3X signal voltage that is supplied by the ignition control module. The ignition control module interprets the 7x ON-OFF signals as an indication of crankshaft position. The ignition control module must have the 7x signal to fire the correct ignition coil.

The 24X interrupter ring and Hall-effect switch react similarly. The 24X signal is used for better resolution at a calibrated RPM.

### Camshaft Position (CMP) Sensor

The camshaft position sensor is located on the timing cover behind the water pump near the camshaft sprocket. As the camshaft sprocket turns, a magnet in it activates the Hall-effect switch in the camshaft position sensor. When the Hall-effect switch is activated, it grounds the signal line to the PCM, pulling the camshaft position sensor signal circuit's applied voltage low. This is interpreted as a CAM signal. The CAM signal is created as piston #1 is on the intake stroke. If the correct CAM signal is not received by the PCM, DTC P0341 will be set.

### Ignition Coils

Three twin-tower ignition coils are individually mounted to the ignition control module. Each coil provides spark for two plugs simultaneously (waste spark distribution). Each coil is serviced separately. Two terminals connect each coil pack to the module. Each coil is provided a fused ignition feed. The other terminal at each coil is individually connected to the module, which will energize one coil at a time by completing and interrupting the primary circuit ground path to each coil at the proper time.

### Ignition Control Module (ICM)

The ignition control module performs the following functions:

• | It determines the correct ignition coil firing sequence, based on 7x pulses. This coil sequencing occurs at start-up. After the engine is running, the module determines the sequence, and continues triggering the ignition coils in proper sequence.

• | It sends the 3X crankshaft reference (fuel control) signal to the PCM. The PCM determines engine RPM from this signal. this signal is also used by the PCM to determine crankshaft speed for Ignition Control (IC) spark advance calculations.

The 3X reference signal sent to the PCM by the ignition control module is an ON, OFF pulse occurring 3 times per crankshaft revolution.

### Circuits Affecting Ignition Control

To properly control ignition timing, the PCM relies on the following information:

• | Engine load (manifold pressure or vacuum)

• | Atmospheric (barometric) pressure

• | Engine temperature

• | Intake air temperature

• | Crankshaft position

• | Engine speed (RPM)

The Ignition Control (IC) system consists of the following components:

• | Ignition coils

• | Ignition control module

• | 7x crankshaft position sensor

• | 24X crankshaft position sensor

• | Powertrain control module

• | All connecting wires

The electronic Ignition Control Module (ICM) connector terminals are identified as shown in the Electronic Ignition System graphic. These circuits perform the following functions:

• | 3X reference high (CKT 430) - The 7x crankshaft position sensor sends a signal to the electronic ignition control module which generates a reference pulse that is sent to the PCM. The PCM uses this signal to calculate crankshaft position and engine speed (also used to trigger the fuel injectors).

• | 3X reference low (CKT 453) - This wire is grounded through the ICM and assures the ground circuit has no voltage drop between the ICM and the PCM

• | Ignition control bypass (CKT 424) - During initial cranking,the PCM will look for synchronizing pulses from the camshaft position sensor and the 7x crankshaft position sensor. The pulses indicate the position of the #1 piston and the #1 intake valve. Five volts is applied to the bypass circuit at precisely the same time these signals are received by the PCM. This generally occurs within one or two revolutions of the crankshaft. An open or grounded bypass circuit will set a DTC P1350 and the engine will run at base ignition timing. A small amount of spark advance is built into the ignition control module to enhance performance.

• | Ignition Control (IC) (CKT 423) - The PCM uses this circuit to trigger the electronic ignition control module. The PCM uses the crankshaft reference signal to calculate the amount of spark advance needed.

• | 24X reference signal - The 24X crankshaft position sensor increases idle quality and low speed driveability by providing better resolution at a calibrated RPM.

### 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 7x 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 balancer 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.

• | If crankshaft position sensor replacement is necessary, the crankshaft balancer must be removed first. The balancer is a press fit onto the crankshaft; removing the serpentine accessory drive belt and balancer attaching bolt will allow its removal with special tool J 38197. When reinstalled, proper torquing of the balancer attachment bolt is critical to ensure the balancer stays attached to the crankshaft.

• | If a crankshaft position sensor assembly is replaced, check the crankshaft balancer interrupter ring for any blades being bent. If this is not checked closely and a bent blade exists, the new crankshaft position sensor can be destroyed by the bent blade with only one crankshaft revolution!

• | Neither side of the ignition coil primary or secondary windings is connected to engine ground. Although the ignition coil packs are secured to the ignition control module, it is not an electrical connection to ground.

• | Be careful not to damage the secondary ignition wires or boots when servicing the ignition system. Rotate each boot to dislodge it from the plug or coil tower before pulling it from either a spark plug or the ignition coil. Never pierce a secondary ignition wire or boot for any testing purposes! Future problems are guaranteed if pinpoints or test lights are pushed through the insulation for testing.

• | The ignition control module is grounded to the engine block through 3 mounting studs used to secure the module to its mounting bracket. If servicing is required, ensure that good electrical contact is made between the module and its mounting bracket, including proper hardware and torque.

• | A conventional tachometer used to check RPM on a primary ignition tach lead will not work on this ignition system. In order to check RPM, use a Scan Tool.

### Powertrain Control Module (PCM)

The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:

• | Ignitions Control module (ICM).

• | Engine Coolant Temperature (ECT) sensor.

• | Intake Air Temperature (IAT) sensor.

• | Mass Air Flow (MAF) sensor.

• | Trans Range inputs from Transaxle Range switch.

• | Throttle Position (TP) sensor.

• | Vehicle Speed Sensor (VSS).

### Modes of Operation

The ignition system uses the same four ignition module-to-PCM circuits as did previous Delco engine management systems using distributor-type ignition. Ignition Control (IC) spark timing is the PCM's method of controlling spark advance and ignition dwell when the ignition system is operating in the IC Mode. There are two modes of ignition system operation:

• | Bypass Mode.

• | IC Mode.

In Bypass Mode, the ignition system operates independently of the PCM, with Bypass Mode spark advance always at 10 (BTDC. The PCM has no control of the ignition system when in this mode. In fact, the PCM could be disconnected from the vehicle and the ignition system would still fire the spark plugs, as long as the other ignition system components were functioning. (This would provide spark but no fuel injector pulses. The engine will not start in this situation.) The PCM switches to IC Mode (PCM controlled spark advance) as soon as the engine begins cranking. After the switch is made to IC Mode, it will stay in effect until one of the following conditions occur:

• | The engine is turned OFF.

• | The engine quits running.

• | A PCM/IC fault (DTC P1350 or DTC P1361) is detected.

If a PCM/IC fault is detected while the engine is running, the ignition system will switch to Bypass Mode operation. The engine may quit running, but will restart and stay in Bypass Mode with a noticeable loss of performance.

In the IC Mode, the ignition spark timing and ignition dwell time is fully controlled by the PCM. IC spark advance and ignition dwell is calculated by the PCM using the following inputs:

• | Engine speed (24X reference or 3X reference).

• | Crankshaft position (24X reference or 3X reference and Camshaft position PCM input signal).

• | Engine Coolant Temperature (ECT sensor).

• | Throttle Position (TP sensor).

• | Knock Signal (Knock sensor).

• | Park/Neutral Position (PRNDL input).

• | Vehicle Speed (Vehicle Speed Sensor).

• | PCM and ignition system supply voltage.

The following describes the PCM to ignition control module circuits:

• | 3X reference PCM input - From the ignition control module, the PCM uses this signal to calculate engine RPM and crankshaft position. The PCM compares pulses on this circuit to any that are on the Reference Low circuit, ignoring any pulses that appear on both. The PCM also uses the pulses on this circuit to initiate injector pulses. If the PCM receives no pulses on this circuit, the PCM will use the 24X reference pulses to calculate RPM and crankshaft position. The engine will continue to run and start normally, but DTC P1374 will be set.

• | 24X reference PCM input - The 24X reference signal is used to accurately control spark timing at low RPM and allow IC operation during crank. Below 1200 RPM, the PCM is monitoring the 24X reference signal and using it as the reference for ignition timing advance. When engine speed exceeds 1200 RPM, the PCM begins using the, 3X reference signal to control spark timing. If the 24X reference signal is not received by the PCM while the engine is running, a DTC P0336 will be set and 3X reference will be used to control spark advance under 1200 RPM, and Bypass Mode will be in effect at under 400 RPM. The engine will continue to run and start normally.

• | Reference low PCM input - This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares voltage pulses on the 3X or 24X reference input to those on this circuit, ignoring pulses that appear on both. If the circuit is open, or connected to ground at the PCM, it may cause poor engine performance and possibly a MIL (Service Engine Soon) with no DTC.

• | Bypass signal PCM output - The PCM either allows the ignition control module to keep the spark advance at Bypass Mode 10 degrees BTDC, or the PCM commands the ignition module to allow the PCM to control the spark advance (IC Mode). The ignition control module determines correct operating mode based on the voltage level that the PCM sends to the ignition control module on the bypass circuit. The PCM provides 5 volts on the bypass circuit if the PCM is going to control spark timing (IC Mode). If the PCM does not apply 5 volts to the bypass circuit, or if the ignition control module doesn't sense the 5 volts, the ignition control module will control spark timing (Bypass Mode). An open or grounded bypass circuit will set DTC P1361 and the ignition system will stay at Bypass Mode advance.

• | Ignition Control (IC) PCM output - The IC output circuitry of the PCM sends out timing pulses to the ignition control module on this circuit. When in the Bypass Mode, the ignition control module grounds these pulses. When in the IC Mode, these pulses are the ignition timing pulses used by the ignition control module to energize one of the ignition coils. Proper sequencing of the 3 ignition coils, i.e.; which coil to fire, is always the job of the ignition control module. If the IC circuit is grounded when the engine is started, DTC P1361 will set and the ignition system will stay in the Bypass Mode. If the IC circuit becomes open or grounded during IC Mode operation, DTC P1350 or P1361 may set. When this happens, the engine will quit running but will restart. Upon restart following an ignition cycle, DTC P1361 will be set, and the ignition system will operate in Bypass Mode.

• | Knock Sensor (KS) PCM input - The KS system is comprised of A knock sensor, a KS module, and the PCM. The PCM monitors the knock sensor signal to determine when engine detonation occurs. When the knock sensor detects detonation, the PCM retards the spark timing (IC) to reduce detonation. Retarded timing can also be a result of excessive valve lifter, pushrod or other mechanical engine or transaxle noise.

• | Camshaft Position PCM input (CAM signal) - The PCM uses this signal to determine the position of the cylinder #1 piston during its intake stroke. This signal is used by the PCM to calculate true Sequential Fuel Injection (SFI) mode of operation. The PCM compares the number of CAM pulses to the number of 24X and 3X reference pulses. If the cam signal is lost while the engine is running the fuel injection system will shift to a calculated sequential fuel injection mode based on the last cam pulse, and the engine will continue to run. The engine can be re-started and will run in the calculated sequential mode as long as the fault is present with a 1 in 6 chance of being correct.

### How DTCs P1350/P1361 are Set

The IC output circuitry in the PCM issues IC output pulses anytime crankshaft reference signal input pulses are being received. When the ignition system is operating in the Bypass Mode (no voltage on the bypass control circuit), the ignition control module grounds the IC pulses coming from the PCM. The ignition control module will remove the ground from the IC circuit only after switching to the IC Mode. (The PCM commands switching to IC Mode by applying 5 volts on the bypass circuit to the ignition control module.) The PCM monitors its own IC output, and expects to see no pulses on the IC circuit when it has not yet applied 5 volts on the bypass control circuit. When the second 3X reference pulse at the start of crank is seen by the PCM, it applies 5 volts to the bypass control circuit and the IC pulses should no longer be grounded by the ignition control module. The PCM constantly monitors its IC output, and should detect the IC pulses only when commanding the IC Mode.

If the IC circuit is open, the PCM will detect IC output pulses while attempting to start the engine (in the Bypass Mode) due to the ignition control module not being able to ground the IC pulses. Three things will occur:

• | DTC P1350 will set.

• | The PCM will not apply 5 volts to the bypass circuit.

• | The engine will start and run in Bypass Mode.

If IC circuit is grounded, the PCM would not detect a problem until the change to IC Mode is commanded by the PCM. When the PCM applies 5 volts to the bypass control circuit, the ignition control module will switch to IC Mode. With the IC circuit grounded, there would be no IC pulses for the ignition control module to trigger the ignition coils, and the engine may falter. The PCM will quickly revert back to Bypass Mode (turn OFF the 5 volts on the bypass circuit), DTC P1361 will set, and the ignition system will operate in Bypass Mode until the fault is corrected and the engine is stopped and restarted.

If bypass circuit is open or grounded, the ignition control module cannot not switch to IC Mode. In this case, the IC pulses will stay grounded in the ignition control module, and DTC P1361 will be set. The engine will start and run in Bypass Mode.

### Results of Incorrect Operation

An open or ground in the IC or bypass circuit will set DTC P1350 or P1361. If a fault occurs in the IC output circuit when the engine is running, the engine may falter or quit running but will restart and run in the Bypass Mode once the ignition has been cycled. A fault in either circuit will force the ignition system to operate on Bypass Mode timing (10° BTDC), which will result in reduced performance and fuel economy.

The PCM uses information from the engine coolant temperature sensor in addition to RPM to calculate spark advance values as follows:

• | High RPM = more advance

• | Cold engine = more advance

• | Low RPM = less advance

• | Hot engine = less advance

Therefore, detonation could be caused by high resistance in the engine coolant temperature sensor circuit. Poor performance could be caused by low resistance in the engine coolant temperature sensor circuit.

If the engine cranks but will not run or immediately stalls, 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, P0321, P0341, P0336 P1200, P1350 P1361 or P1374 is set, the appropriate diagnostic trouble code chart must be used for diagnosis.

If a misfire is being experienced with no DTC set, refer to Symptoms section for diagnosis.