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Home >> Ford >> 1994 >> F 350 4WD Pickup V8-7.3L DSL Turbo VIN F >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Pinpoint Tests >> Pinpoint Tests >> L - Self Test Output (STO)/"Check Engine" Light >> Test Notes
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Test Notes

You should enter this pinpoint test only when you have been directed here from symptom charts.

To prevent the replacement of good components, be aware that the following non-EEC areas may be at fault:
- fuse, bulb or socket

This pinpoint test is intended to diagnose only the following:
- Self-Test Output (STO)/Malfunction Indicator Lamp (MIL) Circuit
- Powertrain Control Module (PCM)


DESCRIPTION
The CHECK ENGINE light is intended to alert the driver of certain concerns in the closed loop system. The CHECK ENGINE light output is turned on when the strategy detects a concern in certain input/output circuits. The light will remain on as long as the concern is present. Regulations governing this light also require that the Diagnostic Trouble Codes (DTCs) be displayed by the flashing of this light.

CHECK ENGINE Light Functionality
The CHECK ENGINE light is located in the instrument cluster and is amber colored. The CHECK ENGINE light functions in one of three modes:

1. Bulb check - at key-ON the light is turned on for a short duration as a bulb check. If this does not occur, check the wiring, the bulb, and the associated fuse.

2. Detection of certain concerns - the CHECK ENGINE light is used to indicate that one of certain concerns has been detected by the PCM or Injector Driver Module (IDM). Only those concerns which result in a change in power output available from the engine will cause the light to be turned ON. Examples of such concerns are:
a. injector low side short to ground - the PCM will turn OFF 4 cylinders to prevent engine damage.
b. accelerator pedal sensor out of range - the PCM will allow the engine to idle only.

3. Self-Test - output of detected Diagnostic Trouble Codes (DTCs) - SLOW mode - DTCs detected by the PCM or IDM will be flashed to the CHECK ENGINE light in middle, least, most significant digit order (e.g., code 911 would be flashed as 1-1-9). This is normal for PCM using three-digit codes.
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