How To Use The Diagnostic Procedures

WARNING: This page is about a different car, the 2004 Ford Pickup Heritage. However, it is still accessible from the selected car via links, so may be relevant.

Use the information about the vehicle driveability or emission concern to attempt to verify/re-create the symptom. Look for any vehicle modifications or aftermarket items that may contribute to the symptom. A check of any applicable TSBs, if this information is available.
Go to QT: STEP 1: DIAGNOSTIC QUICK TEST . Perform the Quick Test step(s). Follow any notes as directed.
If Diagnostic Quick Test is completed, no DTC(s) were received and no special notes applied, go toSTEP 2: NO DTC(S) PRESENT SYMPTOM CHART INDEX .
Select the symptom that best describes the vehicle symptom (for multiple symptoms select the one that is most noticeable). Go to Step 3: No DTC(s) Present Symptom Chart that is indicated. If no DTC(s) are present and the vehicle's symptom is not listed in the No DTC(s) Present Symptom Chart Index, go to the appropriate service information article to continue diagnosis.
The No DTC(s) Present Symptom Chart contains areas to be tested for diagnosis of the vehicle's symptom. The chart is arranged to place the higher probability, or easiest to test items toward the top of the chart. The technician, however, is not required to follow this order due to reasons such as variations in vehicle type, vehicle repair history or technician experience.
- The System/Component column indicates the areas that will be tested. This column may also contain a quick system/component test.
- The Reference column indicates where to go for the System/Component testing. All references are to pinpoint test steps in REFERENCE VALUES - BI-FUEL CNG unless noted otherwise. If referenced to a Pinpoint Test Step or a service information article, go to the procedures. Follow the directions given in those procedures, including directions to other tests or articles. If a damaged part is found, repair/replace as directed. If no fault is found, and diagnosis in that area is complete, return to the No DTC(s) Present Symptom chart and continue to the next item.
- If a quick system/component test is in the System/Component column, the reference column will indicate where to go if the test failed.
During diagnosis, if directed to test a system/component that is not contained on that vehicle, proceed to the next step.
If the No DTC(s) Present Symptom Chart for the vehicle symptom is completed and no fault is found, return to Step 2: No DTC(s) Present Symptom Chart Index to address the next most prominent symptom. If all diagnosis is complete and no fault is found, it may be helpful to go to PINPOINT TEST Z: INTERMITTENT in the PINPOINT TEST - CNG, FLEX-FUEL & GASOLINE article, for further diagnosis.
Utilize the Customer Information Worksheet and the Bi-Fuel Driveability Diagnostic Form located in REFERENCE VALUES - BI-FUEL CNG , to record customer and test data during diagnosis.
After repair, restore the vehicle by reconnecting any components, removing test equipment, etc. Verify that the vehicle is operating properly and the original complaint is eliminated. If a DTC was present, rerun Diagnostic Quick Test to verify repair and clear any Continuous Memory DTC(s).

NOTE: If a symptom is determined to be intermittent, careful visual and physical underhood inspection of connectors wiring harnesses, vacuum lines, components, etc. is required. The Customer Information Worksheet may contain more detailed symptom information. Before an in-depth diagnosis begins, start the engine and wiggle wires, tap on components, etc., while listening for an indication of a concern (such as rpm change or relay clicking).

Information about engine conditions is stored when a Diagnostic Trouble Code (DTC) that lights the Malfunction Indicator Lamp (MIL) is set. This information is called Freeze Frame Data and may be helpful in diagnosing intermittents. (Refer to the FREEZE FRAME DATA in the DIAGNOSTIC METHODS - CNG, FLEX-FUEL & GASOLINE article, for more information.)