Diagnostic Aids - Ignition System
DiagnosisIf the 18X 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 engine speeds under 400 RPM. The engine will continue to run and start normally
If the 3X reference signal is not received by the PCM while the engine is running, the PCM will use the 18X reference pulses to calculate RPM and crankshaft position. The engine will continue to run and start normally, but DTC P1374 will be set.
If an open Reference Low circuit occurs, poor engine performance may result and possibly a MIL with no DTC.
The PCM generates IC timing pulses anytime crankshaft reference signals are being received. The PCM uses the IC control circuit to send the IC timing pulses to the ignition control module (ICM). When the ignition system is operating in the Bypass Mode (no voltage on the bypass control circuit), the ICM grounds the IC pulses. The ignition system switches to the IC Mode when the PCM applies the 5 volt Bypass signal to the ICM on the Bypass circuit. The ICM switches the IC pulses from ground to allow the PCM to control spark timing. The PCM monitors the IC and Bypass circuits for electrical malfunctions affecting proper ignition system operation. If a malfunction occurs, diagnosis is included in DTC P1351, P1352, P1361 and P1362 diagnostic tables.
Diagnostic Aids
The following information lists important considerations to aid 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 the high voltage secondary ignition components when the engine is running, or personal injury may result.
^ The dual Hall-effect crankshaft position sensor is the most critical part of the ignition system. If the sensor is damaged so that the CKP 18X or CKP Sync crank sensor pulses are not generated, the engine will not start.
^ There are 4 circuit wires connecting the dual crankshaft position sensor to the ignition control module. If there is a problem with any of the four, the engine will not start (no spark and no injector pulses). The circuits are described as follows:
- The 10 to 12 volt sensor feed for the Hall effect switches from the ignition control module.
- The CKP 18X CKP pulse signal to the ignition control module.
- The CKP Sync pulse signal to the ignition control module.
- The sensor ground circuit for both Hall-effect switches.
^ If the CKP Sync pulses stop while the engine is running, the engine will keep running. The ignition control module remembers the correct ignition coil sequence. However, the engine will not restart after being shut OFF.
^ If the 18X CKP pulses stop while the engine is running, the engine will stop running and will not restart. The loss of the 18X CKP signal to the ICM results in the loss of crankshaft position information and the ICM's ability to generate the 3X reference signals.
^ Crankshaft position sensor clearance is very important The sensor must not contact the rotating interrupter rings at any time, or sensor damage will result. If the balancer interrupter rings are 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 reinstalling the crankshaft balancer, torque the balancer attachment bolt to the proper specifications. This is critical to prevent crankshaft damage and ensure the balancer stays attached to the crankshaft.
^ If a crankshaft position sensor assembly is replaced, inspect the crankshaft balancer interrupter rings for bent blades. If a bent blade exists, the new crankshaft position sensor can be destroyed within 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. Do not pull on the ignition wire(s) without rotating each boot to dislodge it from the plug or coil tower. Never pierce a secondary ignition wire or boot for any purpose. 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 a ground wire to the ignition control module bracket mounting stud. If servicing is required, ensure that good electrical contact is made between the ground and the 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. To check RPM, use either of the following items:
- A tachometer designed with an inductive pickup, used on the secondary side of an ignition system. These tachs are identified by a clamp that goes around a spark plug wire. Set the tach to 2-cycle operation. The 2-cycle setting is required because spark plugs on this engine fire every time the piston is at the top of its stroke. If a 2 cycle selection is not available, divide the indicated 4 cycle reading by 2.
- A scan tool.