Isuzu Trooper TOD check light

1998 Trooper. Has Traction on Demand 4x4.Check light blinks in the TOD gauge when in 4 wheel drive. Apparently I don't have drive to front wheels in high range but low range shows it has locked 4 wheel drive. What is going on? And can I drive it in low range? Thanks

Most likely one or both of the vacuum switches that control Lock/Unlock of the front axle is bad. Same thing happened to me about a year ago (only the Lock one was bad, had a leak).
The service manual has a step-by-step to trouble shoot it.


BTW it's only sold as an assy.
St Charles Isuzu has the best price and free shipping.

Is the blinking happening only in 4L? If so, it could be as simple as the 4L should only be set in neutral, not in any other position?