Chart A-1 Engine Control System Fault Telltale Inop

DESCRIPTION
The "Engine Control System Fault" lamp is powered through the Instrument Panel Cluster (IPC) and grounded by the ECM Pin A 19 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 Now or Service Soon message is set.
ECM Pin A19 is turned on in conjunction with a code with Service Now or Service Soon message. If a trouble code is set, the ECM will send a Service Now or Service Soon status to the BCM over the UART data link. At the same time, the ECM grounds Pin A19 to turn on the "ENGINE CONTROL SYSTEM FAULT" telltale.

Notes on Chart A-1
1. If the "ENGINE CONTROL SYSTEM FAULT" 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 the battery, or may be damaged due to electrical overload or water intrusion.
2. Checking for power to the IPC. If no other telltales light, the IPC may not be receiving power. See ECM Trouble Codes for diagnosis. Testing and Inspection
3. Checking for ECM receiving ignition signal.
4. Fault is most likely at the ECM connector or ECM. Before replacing the ECM, see "ECM Replacement Check", Chart C-1 in System Charts. Chart C-1 Vehicle Will Not Enter Diagnostics

Notes on Intermittents
Turn the ignition "ON" and manipulate circuit 419 while observing the "Engine Control System Fault" telltale. If the telltale flashes off, repair intermittent open in circuit 419.