Service Engine Soon Light Inoperative
When engine is started, the ECM grounds terminal A10 to turn off the SERVICE ENGINE SOON light. When ALDL terminal "B" is grounded it alternately grounds and opens ECM terminal A10 to flash a code.
Test Number 1) This tests for an open ECM fuse or an open in the SERVICE ENGINE SOON light circuit, including instrument panel connector and printed circuit board. Normal response is light on.
Test Number 2) This tests for a shorted ECM. Grounded ECM terminal A10 will turn the SERVICE ENGINE SOON light off. If disconnecting ECM turns light on, ECM is shorted. Normal response is light on.
Test Number 3) This tests for a grounded circuit No. 487 from terminal "C" of remote lamp driver to ECM terminal A10. It also checks for an open circuit No. 439 to terminal "B" of remote lamp driver module, a bad ground, or a faulty remote lamp driver. A normal reading is 9-11 volts because of the voltage drop through the remote lamp driver upper resistor. A reading of over 11 volts indicates there is no voltage drop in the remote lamp driver module caused by bad ground or faulty module.
Test Number 4) This tests for an open wire to remote lamp driver terminal "B". Normal reading should be close to battery voltage.
Test Number 5) This tests for a grounded circuit No. 487 from terminal "C" of remote lamp driver to ECM terminal A10. Normal response is light on.