Minimum Function System-Check Engine Light Inop

Fig. 001 - Chart - A-4 Check Engine Light Inoperative:

1. This checks for blown gages fuse or open in "CHECK ENGINE" light circuit, including IP connector, remote lamp driver circuit and "CHECK ENGINE" lamp.
a. Normal response is lamp "ON".
2. This checks for a shorted ECM.
a. Grounded ECM terminal "2" will turn the "CHECK ENGINE" light "OFF". If disconnecting ECM turns light "ON", ECM is shorted.
3. This checks for grounded wire from terminal "C" of lamp driver to terminal "2" of ECM, an open circuit to terminal "B" of lamp driver, a bad ground or faulty lamp driver.
a. 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, thus, a bad ground or faulty lamp driver.
4. This step checks for an open in the wire to terminal "B".
a. Normal voltage is approximately battery voltage.
4a. This checks for an open wire to terminal "E" from the "Check Engine" lamp.
a. With terminal "E" grounded, the lamp should normally light. Lamp "OFF" indicates an open, where lamp "ON" indicates faulty lamp driver connection or lamp driver.
5. This checks for a grounded wire from driver terminal "C" to ECM terminal "2". Normal response is light "ON".