Ignition Coil A Primary/Secondary Circuit Malfunction
The PCM has detected a fault in the primary or secondary circuit of one or more ignition coils. The majority of OBD-II equipped vehicles utilize a “coil on plug” system to provide ignition spark. In this system, an ignition coil is secured to the engine in a manner that allows for the use of a small spark plug wire or plug boot. Each ignition coil is electronically controlled by the PCM.
Code Set Parameters
This type of code pertains to the electrical circuitry between the PCM and the individual (or multiple) ignition coils, as well as the coils themselves. Typical designs provide a switched supply of battery voltage to the ignition coil, with a pulsing ground (supplied by the PCM) to activate ignition spark and control ignition timing. Variations in ignition coil circuit voltage that differ by greater than 10-percent from the manufacturer’s reference voltage will cause a code to be stored and a service engine soon lamp to be illuminated.
Symptoms may include a stored code and the illumination of the malfunction indicator lamp, accompanied by a misfire at idle or choppy acceleration. A general lack of overall engine performance is also a likely symptom. Other injector circuit or misfire codes may also be present. Some OBD-II systems also disable the fuel injector on the affected cylinder.
The most likely causes of this code are a faulty ignition coil, shorted or open wiring in the ignition coil driver circuit from the PCM, a faulty or corroded connector for the ignition coil, or a faulty PCM. PCM failure is rare.
Technicians report that maintenance tune ups are frequently performed (unsuccessfully) to correct this malfunction. This is not to say that the tune up was not overdue, but a thorough diagnosis must be performed first to pin point the exact malfunction. Open circuits in the ignition coil circuit are often found on top of the engine due to wildlife damage.
- Many OBD-II equipped vehicles employ an ignition system that utilizes an individual coil for each cylinder
- The coils are typically mounted near the spark plugs so that either a short spark plug wire or spark plug boot may be used to insulate the high-voltage spark as it is transferred from the coil to the spark plug
High-voltage spark is initiated with a pulsed electrical circuit
- Most coil over ignition systems use a two wire electrical connector
- One wire supplies switched battery voltage (usually 12.6 to 13.8-volts) and the second wire delivers a pulsed ground signal from the PCM
- The pulsed ground signal interrupts the circuit abruptly and causes the magneto inside of the coil to emit a high voltage spark
- This spark is transferred to the spark plug where it is used to ignite the air/fuel mixture in the combustion chamber and cause an explosion.
A scanner, an oscilloscope, and a digital volt/ohmmeter will be helpful in diagnosing this code
- If an oscilloscope is not available, then the digital volt/ohmmeter can be used
- This can be accomplished using the digital volt/ohmmeter placed on the AC Hertz setting
Proceed with your diagnosis by performing a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- After the codes are cleared, operate the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
Continue by determining if the engine is actually misfiring regularly
- In some instances, it will be necessary to place a load on the engine in order to make it misfire regularly
- This can be accomplished by using a helper to sit inside the vehicle with the parking brake set
- If the helper puts the gear shift selector in “drive” (automatic transmission equipped vehicles only - manual transmission equipped vehicles must be tested differently) and pushes very firmly on the brake while gently easing into the accelerator pedal and gradually raising the RPM level, a misfire condition should present itself
- If there is no misfire condition currently present, the problem is likely intermittent and will be much more difficult to diagnose
- Perform a “wiggle test” on each ignition coil to check for loose or corroded prongs in the electrical connector, damaged wiring, or loose connectors
- Inspect the wiring harness to make sure that it is not damaged by wildlife or rubbing/vibrating against hot or sharp objects
- Repair open or shorted wiring or connectors as required, reset the PCM codes, and test drive to make sure the problem is rectified.
If there is currently a misfire present, then you may disconnect/reconnect ignition coil connectors individually until the affected cylinder is isolated
- If a cylinder specific ignition coil code is present, begin this process with the indicated cylinder
- After cylinder isolation has been accomplished use the digital volt/ohmmeter, set to AC Hertz, to test for a Hertz (Hz) signal to the ignition coil
- If a Hz signal of between 5 and 20 is discovered, then the ignition coil is faulty
- Replace it, reset the code, and test drive to make sure the problem is fixed
- If no Hz signal is detected in the affected circuit, use the digital volt/ohmmeter to check for voltage on the coil driver circuit (from the PCM)
- If battery voltage is present suspect a shorted (to voltage) wire in this circuit
- Locate the short and repair it as necessary
- If no voltage is detected in the coil driver circuit, then disconnect the electrical connector from the PCM and test for continuity in the circuit
- If no continuity is found, repair the open circuit as required
- If continuity between the coil connector and the PCM connector is detected, test for continuity between the circuit and ground
- There should be no continuity between ground and the coil driver circuit
- If continuity is found, locate and repair the shorted (to ground) wire, reset the code, and test drive the vehicle.
If you have reached this point and no problem has been found you may suspect a faulty coil driver in the PCM
- Before condemning the PCM make sure that the input readings necessary to activate the coil driver are present
- Crankshaft sensor and camshaft sensor codes should have been addressed before beginning a diagnosis for any ignition coil code