After fixing a problem with the four wheel drive system of a 1999 Blazer (or similar S series) you may find that you have low range 4 wheel drive or 2 wheel, but no 4HI. If this happens, it is very likely that a “code 2″ has been set in the TCCM (Transfer Case Control Module).
To check for this:
On the diagnostic connector under the dash (driver’s side – 16 pin connector), with the vehicle off, connect pin 13 (5th pin from the left, bottom row) to ground (an easy one is pin 4, top row and one to the left) and turn the key on. Watch the lights on the 4wd buttons – if there is a code, they will flash it out (in this case, 2 flashes).
If you have a code 2, it forces the system to a “safe mode” which only allows 4LO and 2HI.
To clear this, with the ignition off, disconnect the battery for 2.5 minutes (or more – the TCCM actually does take a bit of time to reset), reconnect, turn key on, and try it out.
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