System Check - DFI/PFI System

DFI System Check:

The DFI System Check is an organized approach for identifying a problem caused by the Digital Fuel Injection System. Driver comments normally fall into one of the following areas:

^ Steady "Service Now" or "Service Soon" light;

^ Driveability problem; or

^ Engine will not start or stalls after start

Understanding the chart and using it correctly will reduce diagnosis time and prevent the unnecessary replacement of parts.

1. The illumination of the "Service Now" and "Service Soon" lights with the engine cranking confirms battery and ignition voltage to the Electronic Control Module (ECM).

2. If one or both of these telltales are not illuminated during crank, see Chart A. 1 for diagnosis. If both telltales illuminate during crank, start engine and note which telltale if any, is illuminated with the engine running before entering diagnostics. If diagnostics cannot be entered, see "Self Diagnostic System Check". If the engine will not start or stalls after start, see Chart A-3. Note any hard trouble codes which are present at this time. Hard trouble codes are given in the second pass and preceded by ".E.E" for ECM codes and ".F.F" for BCM codes. If code E13, E44 or E45 is present, proceed to chart A-6, A-7, or A-8 respectively for diagnosis. If any additional hard codes are present, start with the diagnosis of the lowest trouble code. The text for many trouble trees contain helpful information. However, with the exception of codes E13, E20, E30, E39, E44 and E45, diagnostic charts cannot be used to diagnose intermittent failures or good parts will be replaced. If additional diagnosis is needed, see "Diagnosis by Symptom".

3. If the Service Now and/or Service Soon telltale was illuminated prior to entering diagnostics and there were not any current trouble codes stored, then refer to Chart A-2 for diagnosis.

4. If no additional trouble codes were stored, Perform the "Field Service Mode Check" (contained within DFI System Check). It is essential in the diagnosis of symptoms to determine if the closed loop fuel system is controlling properly. The engine must be at normal operating temperature and running at a constant speed while performing the Field Service Mode Check.

A. Closed loop confirms that the oxygen sensor information is being used by the ECM to control fuel delivery, and that the system is operating normally. Oxygen sensor signal voltage (parameter P.O.7) will swing rapidly from below 0.35 to above 0.55 volts.

B. Open loop indicates that oxygen sensor voltage information is unusable. Oxygen sensor signal voltage parameter P.0.7 is remaining between 0.35 and 0.55 volts. The system is designed to remain in open loop from 30 seconds to 2 minutes after the engine starts and reaches normal operating temperature (above 85°C). If the system fails to go to closed loop refer to Chart A-6 for diagnosis.

C. If the oxygen sensor status light ("ECON" annunciator on CCP) is off all or most of the time, the engine operation is running a lean fuel mixture. Refer to Chart A-7.

D. If the oxygen sensor status light ("ECON" annunciator on CCP) is on all or most of the time, the engine operation is running a rich fuel mixture. For diagnosis refer to Chart A-8.

E. If the oxygen sensor status light ("ECON" annunciator on CCP) turns off and on at least once every 2 seconds the system is operating properly. Refer to "Diagnosis by Symptom".

5. Diagnose oxygen sensor codes first. Use charts A-6, A-7, A-8 for hard or intermittent codes E13, E44 or E45 respectively. If hard or intermittent code E13 is accompanied by code E44, use chart A-7. If hard or intermittent code E13 is accompanied by code E45, use chart A-8.