Mechanics

CHEVY TRANSFER CASE

1999 Chevrolet Blazer

1999 Chevy Blazer

My 1999 Chevrolet Blazer sometimes switches from 2 wd to 4wd hi & lo. The lights for all 3 drive modes will come on all at once the car will still drive. This problem does not occur everytime we drive the car it just happens randomly. We were told that the chain in our transfer case was thin & loose and that we needed new bearings but in order to replace these parts the entire transfer case would have to be rebuilt/replaced. Any suggestions?
Avatar
Nreich2k9
July 29, 2010.



The first step is having the codes read, these codes wont turn the service engine light on, they are B and U codes. But if you want to hunt in the dark here's a few tests: ALL SHIFT SELECT BUTTONS REMAIN LIT 1. If this diagnostic was referred from another test, go to next step. If diagnostic started here, perform FUNCTION TEST under DIAGNOSIS & TESTING, then go to next step. 2. Turn ignition off for at least 6 seconds, then turn ignition on (engine off). If mode and range shifts can now be made, go to next step. If mode and/or range shifts cannot be made, go to step 8. 3. If shift modes can be made from 2HI to 4HI to 2HI, go to next step. If shift modes cannot be made, go to step 7. 4. Turn ignition on (engine off). Check for battery voltage at TCCM terminal D2 (Light Green/Black wire) and terminal D16 (Purple wire). See Fig. 2. If battery voltage is present at both pins, see RETRIEVING CODES under DIAGNOSIS & TESTING. If battery voltage is not present, go to next step. 5. Turn ignition off. Check for open in Purple wire and Light Green/Black wire between select switch and TCCM. If open was found, go to next step. If no open was found, see RETRIEVING CODES under DIAGNOSIS & TESTING. 6. With ignition off, repair open circuit(s), then go to FUNCTION TEST under DIAGNOSIS & TESTING. 7. Turn ignition on (engine off). If 2HI cannot be selected, check for open between TCCM terminal C4 (Dark Green/White wire) and shift select switch. If 4HI cannot be selected, check for open between TCCM terminal C5 (Gray/Black wire) and shift select switch. If open is found, return to step 6. If no open is found, see RETRIEVING CODES under DIAGNOSIS & TESTING. 8. Turn ignition on (engine off). Check for open between TCCM terminal D5 (Red/White wire) and motor/encoder. If an open is found, return to step 6. If no open is found, see RETRIEVING CODES under DIAGNOSIS & TESTING. MORE THAN ONE SHIFT SELECT BUTTON REMAINS LIT 1. If this diagnostic was referred from another test, go to next step. If diagnostic started here, perform FUNCTION TEST under DIAGNOSIS & TESTING, then go to next step. 2. If 2HI button remains lit, check for ground in Light Green/Black wire between shift select switch and TCCM. If 4HI button remains lit, check for ground in Tan/Black wire between shift select switch and TCCM. If 4LO button remains lit, check for ground in Purple/White wire between shift select switch and TCCM. If circuit is grounded, go to next step. If circuit is not grounded, see RETRIEVING CODES under DIAGNOSIS & TESTING. 3. Ensure ignition is off. Repair ground condition in appropriate wire circuit. Restore system, then go to FUNCTION TEST under DIAGNOSIS & TESTING.

Function test Perform first!
Test Procedure 1. Place transmission in Park, turn ignition off and wait at least 6 seconds. Turn ignition on (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, go to step 2 under TEST RESULTS. 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, go to step 4 under TEST RESULTS. 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, go to step 5 under TEST RESULTS. 4. Apply parking brake. Place transmission in Park (A/T) or 1st gear (M/T). Turn ignition on (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, go to step 7 under TEST RESULTS. 5. Turn ignition on (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, go to step 7 under TEST RESULTS. 6. Press transfer case 2HI shift select button and shift transfer case to 2HI position. Place transmission in Park (A/T) or 1st gear (M/T). Turn ignition off. Using a jumper wire, ground DLC pin No. 13. Turn ignition on (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, go to step 8 under TEST RESULTS. Test Results 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 under SYMPTOM TESTS. 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. Shift transfer case to 4HI, then 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, go to step 5. 4. Turn ignition on (engine off). Place transmission in neutral. 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 under SYMPTOM TESTS. 5. If more than one shift select button stays lit, see MORE THAN ONE SHIFT SELECT BUTTON REMAINS LIT under SYMPTOM TESTS. If more than one shift select button does not stay lit, see REDUCED OR NO MODE & RANGE SHIFT OPERATION under SYMPTOM TESTS. 6. Set parking brake. Place transmission in Park (A/T) or 1st gear (M/T). Turn ignition on (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, go to step 8. 7. With ignition on (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 RETRIEVING CODES under DIAGNOSIS & TESTING. If 4LO shift select button does not react as indicated, see REDUCED OR NO MODE & RANGE SHIFT OPERATION under SYMPTOM TESTS. 8. If transfer case range shifts to 4LO, see ALL SHIFT SELECT BUTTONS REMAIN LIT under SYMPTOM TESTS. If transfer case range does not shift to 4LO, see REDUCED OR NO MODE & RANGE SHIFT OPERATION under SYMPTOM TESTS.

Merlin2021
Jul 30, 2010.