No Engine Braking With O/D Cancelled, Manual "1" & "2" Have Engine Braking

Check for poor engine performance. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. Perform QUICK TEST . Record DTCs. Perform TEST G  under SYSTEM TESTS. Repair as necessary. Clear DTCs and perform TRANSMISSION DRIVE CYCLE TEST  under DIAGNOSIS & TESTING. Repeat QUICK TEST  and ensure DTCs are not present.