Chart A-1 Engine Control System Lamp Inoperative

Chart A-1 (1 Of 2):

Service Engine Soon Lamp Circuit:

DESCRIPTION:

The Engine Control System (ECS) lamp is powered through the 10 AMP fuse number 18 in the fuse block, and grounded by the ECM Pin "C1" to illuminate. The ECS telltale will bulb check at key "ON", is illuminated steadily during cranking, and is illuminated whenever a trouble code with service message is set. If a service trouble code is set, the ECM will send a service status to the BCM over the Universal Asynchronus Receiver Transmitter (UART) data link. At the same time, the ECM grounds Pin "C1" to turn "ON" the ECS telltale.

NOTES ON CHART A-1:

1. If code E018 is present, diagnose code E018 before proceeding. The ECS lamp illuminates on cranking only if the crank input is present to the ECM.

2. If code B334 is current ("No ECM Data" is displayed) then go to CHART A-1 continue to check for loss of power or ground to the ECM.

3. If "Stop Engine/Oil" lamp is displayed at key "ON", engine "OFF", then power to the cluster telltales are ok. Continue to diagnose for location of open ground circuit to the ECS telltale or for blown ECS telltale bulb.

4. Starting at the ECM, this branch of the chart follows CKT 325; grounding CKT 325 as the ECM would do to turn the bulb "ON." If a ground at a given point on CKT 325 brings the telltale "ON", then the circuit from the grounded point to the telltale is OK.

Chart A-1 (2 Of 2):

DESCRIPTION:

If the ENGINE CONTROL SYSTEM telltale is inoperative and code B334 is current, then the ECM may not be "powering up" at key "ON", may not be receiving full time power from battery, or may be damaged due to electrical overload or water intrusion.

NOTES ON CHART A-1 (CONT'D):

1. Checking for switched ignition power to ECM.

2. Checking for ground to ECM. Pin A12 and Pin D1 are redundant grounds - if either ground is OK, the ECM should be able to operate normally. If both grounds are open, the ECM will not power up.

3. Checking for full time memory voltage supply to ECM. Pin C16 and B1 are redundant power supplies to the ECM. If either power supply is OK, the ECM can operate normaly.

4. If power grounds, and connections are OK, then be sure to perform CHART C-1 before replacing ECM. The ECM may have been damaged by electrical overload due to a low resistance component.