1998 GMC Jimmy 4WD will not engage

FUNCTIONAL TEST 1. Place transmission is Park position, turn ignition off and wait at least 6 seconds. Turn ignition to run position (engine off) and watch 3 shift select buttons. If all 3 buttons blink once, go to next step. If all 3 buttons do not blink once, see step 2) in FUNCTIONAL TEST FAILED. 2. During step 1), if one button stayed lit to indicate transfer case shift position, go to next step. If one button did not stay lit, see step 4) in FUNCTIONAL TEST FAILED. 3. Shift transfer case to 4HI, to 2HI, then back to 4HI. If transfer case mode shifts between 4HI and 2HI, go to next step. If transfer case mode does not shift between 4HI and 2HI, see step 5) in FUNCTIONAL TEST FAILED. 4. Apply parking brake. Place transmission in Park position (A/T) or in 1st gear (M/T). Turn ignition to run position (engine off). Place transfer case in 4HI position. Press 4LO shift select button. If 4LO shift select button blinks for 30 seconds then stops when 4HI button illuminates, go to next step. If button blinking does not respond as indicated, see step 7) in FUNCTIONAL TEST FAILED. 5. Place ignition in run position (engine off). Shift transfer case to 4HI position and press 4LO shift select button while noting blinking. Place transmission in Neutral (A/T) or push clutch to floor (M/T). If 4LO shift select button stops blinking and stays lit when transmission is shifted as indicated, go to next step. If 4LO button does not respond as indicated, see REDUCED OR NO MODE & RANGE SHIFT OPERATION test. 6. Press transfer case 2HI shift select button and shift transfer case to 2HI position. Place transmission in Park (A/T) or in 1st gear (M/T). Turn ignition off. Using a jumper wire, ground DLC pin No. 13. Turn ignition to run position (engine off). If all 3 shift select buttons blink once then stay off, test is complete, system is functioning normally. If all 3 shift select buttons do not respond as indicated, see step 8) in FUNCTIONAL TEST FAILED. Page 1 of 1 DIAGNOSIS - NEW VENTURE 233 -1998 GMC Jimmy 2/28/2009
FUNCTIONAL TEST FAILED 1. If any of the 3 shift select buttons blinked once, go to next step. If any button did not blink once, see ALL SHIFT SELECT BUTTONS DO NOT LIGHT test. 2. If one shift select button stayed lit to indicate transfer case shift position, go to next step. If one shift select button did not stay lit to indicate position, go to step 4). 3. If transfer case mode shifts between 4HI and 2HI, go to next step. If transfer case mode does not shift between 4HI and 2HI, go to step 5). 4. Turn ignition to run position (engine off). Place transmission in Neutral position. Push vehicle forward about 5 feet. If transfer case mode shifts between 4HI and 2HI, perform diagnosis of transfer case mechanical components. If transfer case mode does not shift between 4HI and 2HI, see REDUCED OR NO MODE & RANGE SHIFT OPERATION test. 5. If more than one shift select button stays lit, see MORE THAN ONE SHIFT SELECT BUTTON REMAINS LIT test. If more than one shift select button does not stay lit, go to next step. 6. Set parking brake. Place transmission in Park (A/T) or 1st gear (M/T). Turn ignition to run position (engine off). Press 4LO transfer case shift select button. If 4LO button blinks for 30 seconds, go to next step. If 4LO button does not blink for 30 seconds, to go step 8). 7. With ignition in run position (engine off), press 4LO shift select button and note blinking. Place transmission in Neutral (A/T) or depress clutch pedal (M/T). If 4LO shift select button stops blinking and stays lit when transmission is shifted as above, see PERFORM A DIAGNOSTIC ON TCCM. If 4LO shift select button does not react as indicated, see REDUCED OR NO MODE & RANGE SHIFT OPERATION test. 8. If transfer case range shifts to 4LO, see ALL SHIFT SELECT BUTTONS REMAIN LIT test. If transfer case range does not shift to 4LO, see REDUCED OR NO MODE & RANGE SHIFT OPERATION test. Page 1 of 1 DIAGNOSIS - NEW VENTURE 233 -1998 GMC Jimmy 2/28/2009
SELF-DIAGNOSTIC SYSTEM RETRIEVING DTCS 1. Turn ignition off for at least 6 seconds. Locate DLC near right side of steering column. Install jumper wire between diagnostic pigtail (Orange wire at DLC, terminal No. 13) and ground. 2. Turn ignition to run position (engine off). Observe shift select buttons. If all shift select buttons blink once at same time then stop, no DTCs are stored. If only one code is stored, that code will blink repeatedly, with a 3 second delay between sequences. If more than one code is present, next code will flash after a 3 second delay, then sequence will repeat. Count number of blinks for each code. See Fig. 1. 3. Write down all DTCs. After retrieving DTCs clear TCCM memory and repeat procedure. See CLEARING DTCS. If DTCs return, perform appropriate DTC test. See DTC DEFINITIONS under SELF-DIAGNOSTIC SYSTEM. Fig. 1: Reading Diagnostic Trouble Code Courtesy of GENERAL MOTORS CORP. DTC DEFINITIONS DTC "1" When ignition switch is in run position, TCCM tests whether RAM standby power (maintained battery power) to TCCM was lost since ignition was last turned off. When power is interrupted to TCCM (pin No. 6), TCCM stores loss of RAM standby power and sets DTC "1". If DTC "1" is present, check circuit between TCCM and fuse block. Repair circuit as necessary. If circuit is okay, replace TCCM. DTC "2" During electronic shifting, TCCM checks motor/encoder for normal operation. If motor/encoder does not function properly, TCCM stores motor/encoder failure DTC "2". If DTC "2" is present, check circuits between TCCM and motor/encoder. If circuits are okay, replace motor/encoder. If circuits are repaired, perform FUNCTIONAL TEST. NOTE: Diagnostic Trouble Codes (DTC) are displayed on 3 transfer case shift select buttons. When proper conditions are met, select buttons will blink to indicate DTC from "1" to "4". NOTE: To diagnose affected DTC(s), refer to DIAGNOSTIC TESTS. Tips     Click a link to view tip Tech1 Tip: DTC 2.
DTC "3" Each time electronic shift motor is turned on or off, TCCM tests whether motor functions properly. If motor does not function properly, TCCM stores motor circuit failure DTC "3". Shift select buttons will blink to alert driver of problem. If DTC "3" is present, check circuits between TCCM and electric shift motor. If circuits are okay, replace electric shift motor. If circuits are repaired, perform FUNCTIONAL TEST. DTC "4" Each time ignition is turned on, TCCM tests memory, program and internal system to ensure TCCM is operating properly. If fault is detected in TCCM, it stores a RAM/ROM memory failure DTC "4". If DTC "4" is present, replace TCCM. CLEARING DTCS Turn ignition off. Remove 10-amp courtesy lamp fuse No. 8. Wait at least 40 seconds and reinstall fuse. Cycle ignition on and off 5 times. Now all DTCs will be cleared from TCCM memory. NOTE: DTCs will not clear if 10-amp courtesy lamp fuse No. 8 is not removed for at least 30 seconds.

DTC 3 in your case could be a simple problem with the connectors, GM has a tech bulliten out about thier wiring and connectors, "suspect connector leads befor the module as the failure" Smetimes even when a connection looks good, it's not!