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Category: Chevy
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Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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Chevrolet Tahoe 4X4: -service 4 wd light comes on randomly..lights lit

Resolved Question:


2003 Chevrolet Tahoe 4X4

--service 4 wd light comes on randomly
--last time vehicle was in Auto 4wd, it went to 2wd by itself, all lights lit up for 4wd selection at the same time, then went out. Has been in 2wd since

history codes:


currently 4wd drive works when commanded to
Submitted: 6 years ago.
Category: Chevy
Expert:  AMEDEE replied 6 years ago.
Hello and Welcome to Just Answer. My name is XXXXX XXXXX I will try my best to assist you and your 100% satisfaction is my goal. I have been working on these vehicles for over 10 years so I am very familiar with this system and how they work. However, keep in mind, that I need some solid concrete facts/evidence/clues from you in order to give you a good answer about your vehicle. Please realize that all my answers are based solely on the info that you provide me with....

If you clear the codes, which code comes back first?

Are you saying that the 4wd works when you turn it on by way of a scanner...or by way of the switch?

Do you have access to a scanner?
Customer: replied 6 years ago.

*4wd works by switch


*no current codes presently


*all codes presented were history codes

Expert:  AMEDEE replied 6 years ago.
There is in fact a TSB out about this problem. It says to reprogram the TCCM. It is TSB number 03-04-21-005.

Here it is.

Date: June, 2003

Service 4WD Light On, 4WD Inoperative, Diagnostic Trouble Codes (DTC) C0300 and/or C0305 Set (Reprogram Transfer Case Control Module (TCCM))

2003 Chevrolet Avalanche, Silverado, Suburban, Tahoe, TrailBlazer
2003 GMC Envoy, Sierra, Yukon, Yukon XL
2003 Oldsmobile Bravada with 4WD (RPOs NP4, NP8)


Some customers may comment that the Service 4WD light is on and/or the 4WD is inoperative.


Condition may be caused by a TCCM calibration issue.


Follow the service procedure below for diagnosis and repair of this condition.
With a scan tool, select the TCCM DTCs.
If TCCM DTCs C0300 or C0305 are present in the TCCM, continue with TCCM reprogramming in Step 2. If TCCM DTC C0374 is present with any of the above codes, disregard and clear the DTC and continue with TCCM reprogramming in Step 2.
If TCCM DTC C0374 is present alone with none of the above listed codes, additional diagnosis is required. If TCCM DTC C0550 is present, refer to DTC C0550 in SI for proper diagnosis of the applicable vehicle. Clear all DTCs and reprogram the TCCM with TIS version 3.5 or newer released to the dealers on 3-22-03.

Edited by AMEDEE on 2/16/2011 at 11:24 PM EST
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