2007 Jeep Compass

Diagnosis & Testing

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Specific to:

Jeep Compass 2007-2009

Jeep Patriot 2007-2009

The Powertrain Control Module (PCM) automatically regulates the spark advance to fire the spark plugs according to input from various engine sensors. The input signals are then used to compute the optimum ignition timing for the lowest exhaust emissions and the best driveability. During the crank-start period, the ignition timing advance is set to ensure quick and efficient starting.

The amount of electronic spark advance provided is determined by 4 input factors: coolant temperature, engine RPM, throttle position, and available manifold vacuum. On some late model systems, intake manifold temperature is also used. Gear selection may also be a factor.

Battery voltage is supplied to each coil by the Automatic Shutdown (ASD) relay. The PCM opens and closes each coil ground circuit at a specific time to fire the plug.

By controlling the coil ground circuit, the PCM is able to set the base timing and adjust the ignition timing advance. This is done to meet changing engine conditions.

Base ignition timing is set by the PCM and is not adjustable.

Component tests are limited to checks of the spark plugs and coils. Specialized analysis equipment is needed for more in-depth troubleshooting.


WARNING
Do not run the engine with a coil disconnected. Do not attempt to ground a coil to the engine to check for spark. Sensitive components could be ruined or the extremely high voltage could cause serious injury or death.

To test the ignition system, perform the test procedures in a particular sequence. Start with the secondary spark test, commence to the coil test (located under the coil procedures later in this section) and, finally, perform the failure-to-start test. Performing the tests in this order will narrow down the ignition system problem in the easiest manner.

Failure-To-Start Test



Specific to:

Jeep Compass 2007-2009

Jeep Patriot 2007-2009

Before proceeding with this test, refer to the testing procedures for the ignition coil, later in this section.

  1. Using a Digital Volt/Ohmmeter (DVOM) measure the voltage from the negative (-) battery terminal to the positive (+) battery terminal. The voltage should be at least 12.66 volts. This amount of voltage is necessary for an accurate inspection of the system.
  2.  
  3. Detach the ignition coil harness connector.
  4.  
  5. Connect a suitable test light to the B+ (battery voltage) terminal of the ignition coil electrical connector and ground. The B+ (battery voltage) wire for the DIS coil is dark green with an orange tracer. Do not spread the terminal with the test light probe.
  6.  
  7. Turn the ignition key to the ON position. The test light should flash ON and then OFF. Leave the ignition key ON .
    1. If the test light flashes momentarily, the PCM grounded the ASD relay. Proceed to the next step.
    2.  
    3. If the test light did not flash, the ASD relay did not energize. This is caused by either the relay or one of the relay circuits.
    4.  

  8.  
  9. Crank the engine. (If the key was placed in the OFF position in Step 4, turn the key to the ON position before cranking. Wait for the test light to flash once, then crank the engine).
    1. If the test light momentarily flashes during cranking, the PCM is not receiving a crankshaft position sensor signal. Use a DRB or equivalent scan tool to test the sensor and related circuitry.
    2.  
    3. If the test light did not flash during cranking, unplug the crankshaft position sensor connector. Turn the ignition key to the OFF position. Turn the key to the ON position, wait for the test light to momentarily flash once, then crank the engine. If the test light momentarily flashes, the crankshaft position sensor is shorted and must be replaced. If the light did not flash when the engine was cranked, the cause of the no-start condition is in either the crankshaft or camshaft position sensor 8-volt supply circuit, or the camshaft position sensor output or ground circuits. Use a DRB or equivalent scan tool to test the camshaft position sensor and related circuitry.
    4.  

  10.  
  11. To test ignition coil resistance, refer to the following table.

    Click image to see an enlarged view

    Fig. Ignition coil resistance table

  12.  

Secondary Spark Test



Specific to:

Jeep Compass 2007-2009

Jeep Patriot 2007-2009


CAUTION
The ignition system generates approximately 40,000 volts. Personal injury could result from contact with this system.

Since the coil pack contains independent coils in the assembly, each coil must be checked individually. The 2.0L and 2.4L engines use a coil-on-plug design.

  1. Remove the ignition coil from the No. 1 spark plug, then insert a clean spark plug into the spark plug boot.
    NOTE
    Due to the high secondary voltage and risk of electrical shock, it is advisable to wrap a thick, dry cloth around the boot before grasping it.


    WARNING
    Spark plug wire damage may occur if the spark plug is moved more than 1 / 4 inch (6mm) away from the engine ground.

  2.  
  3. Ground the plug to the engine (touch the spark plug metal body to the engine block or other piece of metal on the vehicle).
  4.  
  5. Crank the engine and look for a strong, blue spark across the electrodes of the spark plug.
  6.  
  7. Repeat the test for the remaining cylinders. If there is no spark during all cylinder tests, refer to the failure-to-start test. If one or more tests indicate irregular, weak or no spark, refer to the coil test.

    Click image to see an enlarged view

    Fig. The spark plug must be grounded to a metal part of the vehicle, such as the engine block

  8.  

 
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