Chart A-5 Check Engine Light Inoperative

Chart A-5:

Chart A-5 Wiring Diagram:

CIRCUIT DESCRIPTION:

When the engine is started, the ECM grounds terminal "G" to turn out the "CHECK ENGINE" light. It alternately grounds and opens it to flash a code.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. This checks for open fuse, or open in "CHECK ENGINE" light circuit, including instrument panel connector, printed circuit, and "CHECK ENGINE" lamp. Normal response is lamp "ON."

2. This checks for grounded CKT 487 from terminal "C" of lamp driver, to ECM terminal "4," an open CKT 439 to terminal "B" of lamp driver, a bad ground or faulty lamp driver. A normal reading is about 9 to 11 volts, because of the drop through the upper resistor in the lamp driver. Over 11 volts indicates there is no drop in the lamp driver. This indicates a bad ground, or faulty lamp driver.

3. This step checks for an open in the wire to terminal "B." Normal voltage is approximately battery voltage.

3A. This checks for an open CKT 439 to terminal "E" from the "CHECK ENGINE" lamp. With terminal "E" grounded, the lamp should normally light. Lamp "OFF" indicates an open, and lamp "ON" indicates faulty lamp driver connection or lamp driver.

4. This checks for a grounded CKT 487 from driver terminal "C" to ECM terminal "4." Normal response is light "ON."