Vehicle On-Board Diagnostics (OBD) System Check
This should be the starting point of any driveability or symptom diagnosis. Perform the Vehicle OBD system check. Refer to Vehicle On-Board Diagnostic (OBD) System Check (Chart 1 of 2) and Vehicle On-Board Diagnostic (OBD) System Check (Chart 2 of 2) in Data Link Communications. This check verifies the communication integrity of all on-board control modules and their self-diagnostic capabilities. If diagnostic trouble codes (DTCs) are stored, go directly to the numbered DTC chart.
Verify Complaint
Verify the customer complaint and locate the correct symptom definition. Check all of the items associated with that symptom in both the complaint/condition and symptom section.
Gather Information
Gather information from all resources available to pinpoint the when, where, why, and how of the symptom. Road test with the customer when possible to completely understand the symptom. Compare the symptom to a similar vehicle to verify this is an abnormal condition. Find out (when applicable) grade of fuel and where purchased, maintenance history (oil changes, etc.), typical driving cycle, etc. Perform a bulletin search focusing on specific symptoms.
Visual Inspection
The importance of the visual inspection cannot be overstressed. Visual inspection can lead to correcting a problem without further testing and can save valuable time. The check should include:
| • | Use of aftermarket equipment (e.g., alarm systems, cellular phones, lighting, CB radio, etc.) |
| • | Use of aftermarket parts (e.g., air filter, PCV valve, spark plugs, fuel filter, battery, etc.) |
| • | Inspect wiring harnesses for proper routing, connections, pinches, chaffing and cuts |
| • | Inspect the powertrain control module (PCM) and component grounds for tightness and evidence of corrosion. |
Customer Snap-Shot Function
The PCM has the capability of running a CUSTOMER SNAP-SHOT function to aid in intermittent diagnosis. In the past, intermittent driveability concerns relied solely on the self-diagnostic capabilities of the on-board diagnostics. With this feature, the customer has the ability to capture engine general information parameters when experiencing driveability concerns to aid in diagnosis. If the vehicle is equipped with cruise control, activation of the function is accomplished simply by toggling the ON/OFF cruise control switch 3 times within 3 seconds. The PCM looks for 3 transitions either OFF or ON within the 3 second window to capture the data. The PCM then sets DTC P1624 and information is stored in the Freeze Frame/Failure Record. The Freeze Frame/Failure Record can be accessed using a scan tool. The PCM will allow only one capture per ignition cycle.
