DFI System Check
The DFI SYSTEM CHECK is an organized approach for identifying a problem caused by DFI system. Driver comments normally fall into one of the following: Steady "SERVICE NOW/SOON" lights, driveability problems, or engine cranks but will not run.
- Lighting of "SERVICE NOW/SOON" lights during cranking confirms battery and ignition voltage to ECM.
- Enter diagnostics and note any hard codes that are present at this time. Hard trouble codes are given during second pass and preceded by ".E.E" for ECM codes and by ".F.F" for BCM codes. If any hard codes are present, start with diagnosis of lowest numbered code.
- If no trouble codes were stored or any intermittent codes were present, see DFI TESTS W/ CODES. The "Field Service Mode Check" (contained within DFI System Check) is essential in diagnosis of symptoms to determine if closed loop fuel system is controlling properly. The engine must be at operating temperature, and running at constant speed while performing "Field Service Mode Check":
- Closed loop confirms that oxygen sensor information is being used by ECM to control fuel delivery, and that system is operating normally. Signal voltage will swing rapidly from below .35 to above .55 volts.
- Open loop indicates that oxygen sensor voltage information is not usable. Signal voltage is constant value between .35 and .55 volts. System will be in open loop from 30 seconds to 2 minutes after engine reaches normal operating temperature. If system fails to go to closed loop, see CHART A-3.
- If oxygen sensor status light ("ECON" light on CCP panel) is on all or most of the time, engine operation is running rich fuel mixture. See CHART A-6.
- If oxygen sensor status light is off all or most of the time, engine operation is running lean fuel mixture. See CHART A-5.
- If oxygen sensor status light blinks off and on, system is operating properly. See DFI TESTS/CODES Article.