Note: This test is for a 4-wire COP with a feedback signal to the ECU. Some 4-wire COPs have two ground pins and no feedback signal: these should be tested as a 3-wire COP (see 3-Wire COP Test).
The trigger signal rises from 0 volts to about 4 volts at coil switch-on and then returns to 0 volts at coil switch-off. The time between these events, called the dwell period or the coil saturation time, is determined by a current-limiting circuit in the vehicle's Electronic Control Module (ECM) or ignition amplifier.
The feedback signal tells the ECU that ignition has occurred. The signal is inverted, so a high level (about 5 volts) indicates the inactive state and a low level (0 volts) indicates a successful ignition. The feedback signal on this engine is common to all four cylinders, so there are four feedback pulses for every engine cycle.
A 4-wire COP has the following connections (pin numbers may vary depending on the type of coil):
In addition to the trigger and feedback signals shown in the waveform above, it is sometimes useful to monitor the positive supply voltage and current and the ground voltage. For instructions on checking the supply and ground/earth pins, see the 3-wire COP test.
Positive supply voltage. This should be close to battery voltage. If it is low or absent then the ignition system is not receiving enough power and the coil will not function.
Supply current. This can be measured using a current clamp ('amps clamp') around the ignition supply wire, either close to the coil or at the fusebox. A pulse should be seen whenever the coil fires. If the supply and trigger voltages are present but there is no supply current pulse, the coil has probably failed open-circuit. If there is a current pulse but no ignition, the coil output or spark plug may be short-circuited.
Ground. A small pulse will be seen on this signal during ignition as the coil draws current from the battery, but the pulse height should not exceed a few hundred millivolts. A larger voltage indicates too much resistance in the ground wiring, which could cause an ignition fault.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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August 19 2016
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