Communication Problems:
Seriously, Just Talk to Me
T
he NV233 four-wheel drive systems are found on Blazer, S-10 trucks, and Tahoe appli-
cations. A common unit with an all- too-common problem: the scan tool won’t provide data or allow for code retrieval. But it is possible to retrieve codes manually.
Manual Code Retrieval
To retrieve codes manually:
• Locate the data link connector (DLC) near the right side of the steering column. • Install a jumper wire between the diagnostic pigtail (orange wire at DLC terminal 13) and ground. • Key On, Engine Off. • Watch the 4WD selector switch status lights. After about 3 seconds, if there’s
a code in the Transfer Case Control Module (TCCM) system, the 4WD selector switch lights will start to flash. The NV233 transfer case only has
four possible codes, and all are single digit:
Code 1: TCCM Internal Fault Code 2: Encoder Circuit Fault Code 3: Motor Circuit Fault Code 4: TCCM RAM/ROM Fault To clear the codes: • T series — Remove T/L CTSY (20 amp) fuse • K series — Remove T-CASE fuse
34
• Wait 2½ minutes, then reinstall the fuse. • Cycle the ignition 5 times. The codes should be cleared from
the TCCM.
Checking the 4WD Lights
Refer to the TCCM connector
views to determine the correct terminal locations for performing these tests. When attempting to retrieve codes
from the NVG233 transfer case system, you may find 4WD lights that aren’t working. If the 4WD lights won’t light, check the 10-amp gauges fuse (fuse 4) located in the instrument panel fuse block. If the 10-amp gauges fuse is good, inspect the 20-amp 4WD fuse (fuse 19), also located in the instrument panel fuse block. If either fuse is blown, repair the circuit as needed. Next, check the TCCM power feed
circuits at terminals C6, C8, D14 and D15 for 12 volts with the key on, and the ground circuits at terminals C10, D10, D12 and D13 for a good path to ground. The ground path should have less than 0.05 volts. After verifying good power and
ground circuits to the TCCM, turn the key on, engine off, check for power on TCCM terminals C11, C12 and C13. You should have 12 volts on these cir- cuits if the indicator circuits are intact. A quick and easy test for the 4WD
The NV233
by The ATRA Technical
Department
members.atra.com www.atra.com
light system is to ground TCCM termi- nals C11, C12 and C13 one at a time, and see if each 4WD light turns on. If the 4WD lights turn on when
you ground the circuit, the circuits are intact. If the TCCM won’t operate the light, suspect a TCCM problem. While it’s nice to be able to bypass
the scan tool and grab codes, not having scan data can make it difficult to col- lect the information you need to repair the unit. So let’s take a look at some of the more common problems on this system. IMPORTANT: Before replacing
the TCCM, always check the power and ground circuits, and always make sure you don’t have any shorts in the control circuits. Take care of any of these problems before replacing any control module.
Code 1: TCCM Internal Fault
Attempt to clear code 1. If the code resets:
• Key on, engine off. • Check for battery voltage on cir- cuit 1640 (orange wire) at TCCM terminals D14 and D15. If there’s no voltage, check and repair circuit 1640 as needed. • If you have battery voltage at TCCM terminals D14 and D15, check the TCCM ground circuits
GEARS May/June 2010
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