Service Engine Soon Light Inoperative
When engine is started, ECM grounds terminal A10 to turn off SERVICE ENGINE SOON light. When ALDL terminal "B" is grounded, ECM alternately grounds and opens terminal A10 to flash a code.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- This tests for an open ECM fuse or an open in SERVICE ENGINE SOON light circuit, including instrument panel connector and printed circuit board. Light on is normal response.
- This tests for a shorted ECM. A grounded ECM terminal A10 will cause SERVICE ENGINE SOON light to go off. If light comes on after disconnecting ECM, ECM is shorted. Light on is normal response.
- This tests for a grounded circuit between terminal "C" of remote lamp driver and 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. Because of voltage drop through remote lamp driver upper resistor, a normal voltage reading should be 6-11 volts. If voltage is greater than 11 volts, there is no voltage drop in remote lamp driver module due to bad ground or faulty module.
- This tests for an open wire to remote lamp driver terminal "B". Normal reading should be close to battery voltage.
- This tests for a grounded circuit between terminal "C" of remote lamp driver and ECM terminal A10. Light on is normal response.