Chart A2 - "Service Soon" Light On - No Codes Set
NOTE:
As a carryover from the previous year, manufacturer refers to the "SERVICE SOON" light as the "ENGINE CONTROL SYSTEM" light in flow charts. This light was renamed "SERVICE SOON" in late 1988.
The "SERVICE SOON" light is powered through the 10-amp "IGN-1" fuse in fuse block, and grounded by ECM terminal C1 to illuminate. The "SERVICE SOON" light checks the bulb with key on. Light is illuminated steadily during cranking, and is illuminated whenever a trouble code with service message is set. If a service trouble code is set, ECM sends a service status to BCM via the data link. At the same time, the ECM grounds terminal C1 to turn on "SERVICE SOON" light.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Intermittent loose grounds or power connections can cause ECM to repeatedly power-up, power-down or to reset.
- Check for bulb grounded by ECM through terminal C1 or through a circuit fault.
- Remove and replace both ECM connectors and ensure that they are latched. Check MEM-CAL unit for proper orientation, bent terminals, and full seating in socket. Subsitute a known good MEM-CAL unit to see if unit is causing the light to flicker. If test MEM-CAL unit does not correct condition, replace ECM. Be sure to perform CHART C1 - ECM REPLACEMENT CHECK.