Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
2. A visual/physical inspection should include checking the following components:
   • The wiring for proper connections, pinches or cuts.
   • The ECM grounds for being clean and tight.
   • The vacuum hoses for splits, kinks, and proper connections as shown on the Vehicle Emission Information label. Check thoroughly for any type of leak or restriction.
   • For air leaks at the throttle body mounting area and intake manifold sealing surfaces.
3. When all the accumulators are relatively equal, then the misfire is being caused by something that affects the entire engine. When they are not then the misfire is being caused by something that is specific to two or more cylinders.
4. Whenever the misfire is not present operating the vehicle may be necessary to duplicate the conditions in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. Whenever the misfire accumulators start to increment, then misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared.
5. Check fuel for water, alcohol, etc.
6. A basic engine problem that affects all cylinders is the only possibility at this point. (Cam timing, throttle body leak, restricted air flow, etc.)
7. Tests the ignition system voltage output using a spark tester.
8. Replace any spark plugs that are worn, cracked or fouled.
9. Checks for voltage at the ignition feed circuit.
10. Whenever the driver circuit is shorted to ground, the light will be ON steady. When the driver circuit is shorted to voltage or open, the light will be OFF.
11. Since voltage is supplied to the fuel injector on a single circuit, the malfunction could only be a poor connection or open in the fuel injector harness. An open before the harness would result in an "Engine Cranks But Will Not Run" complaint.
12. Before replacing the ECM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.