SMU for All 2002 L-Series (L81) Engine Service Manuals Regarding DTC P0031, P0621, and P1637 Flowcharts

The purpose of this bulletin is to update all 2002 L-Series (L81) Engine Service Manuals at your location.

Please obtain all 2002 L-Series (L81) Engine Service Manuals and make the necessary updates as indicated below.

1. On page 385 (DTC P0621 Flowchart) and page 431 (DTC P1637 Flowchart), write in the following bulleted step after "Raise vehicle." and before "Using DVOM, measure voltage on circuit 225 at the generator ring terminal."

Disconnect generator L-terminal (ring terminal)

2. On page 121 (DTC P0031 Flowchart), write in the following bulleted steps after "Check ENGINE CNTL 3 fuse. Replace and retest if open. If fuse continues to open, check for a short to ground on circuit(s) 2740."

•	Disconnect HO2S bank 1 sensor 1.

•	Using DVOM, measure voltage on circuit 751.