Question about 1994 Chevrolet S-10 Blazer

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4 wheel drive doesnt engage, service 4wd light comes on code co327 changed encoder motor and sensor tried used module had it reprogramed made it so the lights dont work on the switch. HELP

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That is the code for the transfer case control module. It is really expensive to replace, maybe $500 or more. Unfortunately, everytime I have had the code pop up, you will have to have the trans case drained, flushed, and the control module will have to be changed. I am truly sorry for the bad news, but I really hope all works out:(

Posted on Mar 06, 2009

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I have a 1998 Chevy Tahoe I tryed to put my truck is 4wd low and it tryed and keep on blinking and went back to 2wd and blow a fuse and I tryed again and did it again but then the the service 4wd light...

Which 4X4 system does your tahoe have ?
Transfer Case System Description (Selectable 4WD)
The New Venture Gear Model NV243 is an electronically controlled optional transfer case for use on four wheel drive K trucks. The driver selects 2HI, 4HI, or 4LO by pushing one of three illuminating shift select buttons mounted on the instrument panel. The shift select buttons display the transfer case mode and range, self-test, diagnostic trouble codes, and electronic shift mechanical engaging problems.

Transfer Case System Description (Automatic 4WD)
The two speed Auto transfer case system utilizes a part time front axle. The system allows the driver to select the transfer case position with a touch of a button. The following positions can be selected: 4-wheel drive high range (4H), All Wheel Drive (AUTO), 2 Wheel Drive high range (2H), Neutral (N), and 4-Wheel Drive low range (4L).
The Auto Transfer Case (ATC) Control Module controls all the shifting action of the transfer case based on input from the driver as well as information from the Vehicle Control Module (VCM) /Powertrain Control Module (PCM).
4WD (4H or 4L) mode: This is accomplished by engaging the front axle, applying PWM to an electric motor to apply maximum torque, (fully compressing the transfer case clutch plates) to the front axle, then removing the ground on circuit 1569, thus locking the motor in position and stop the PWM to the motor.
AUTO mode: When in this mode of operation, the system should engage the front axle, then it monitors the front and rear propshaft speeds for any speed differences. When the system senses rear wheel slip, a difference of propshaft speed between front and rear, the Auto Transfer Case (ATC) Control Module will use pulse width modulation (PWM) to drive an electric motor. This motor transfers only the required torque to the front wheels to gain additional traction on slippery surfaces up to 75 mph. There is no torque applied to the front wheels until the module senses rear wheel slip.
Throttle anticipation (only operational when in AUTO mode): If the vehicle is below 5 mph and the accelerator is pressed quickly beyond a set point, the system will automatically transfer a percentage of torque to the front wheels to help prevent the rear wheels from slipping, as in a hard acceleration from a stopped position.
The Auto Transfer Case (ATC) Control Module also has the capability of engaging the front axle while the vehicle is in motion. It does this by applying PWM to the electric motor to apply torque to the front axle, this action is used to match the speed of the front and rear propshafts. After the module senses the proper speed, it then supplies a ground on circuit 1570 to engage the front axle.
The Auto Transfer Case (ATC) Control Module will accept a mode shift only when the engine is running and a valid Motor/Encoder signal is present. A mode shift is any shift between 2H, 4H, and AUTO.
The Auto Transfer Case (ATC) Control Module will permit a range shift only if the following conditions are met within 30 seconds of the request:

Automatic 4WD Diagnostic Aids
A Scan Tool reads and displays the following information:
• Diagnostic Trouble code(s)
• Code status bit (are codes set or not)
• Transfer case lock status
• Lamp in the switch/lamp assembly
• Motor/Encoder gear position
• Ignition (3) voltage
• Front propshaft speed sensor (KPH)
• Front axle switch (open/closed)
• Front axle requested position (engaged/disengaged)
• Rear propshaft speed sensor (KPH)
• Mode switch position request
• Park switch (open/closed)
• 4WD (Adapt) Mode Auto bit
• Current Mode corrective action PWM
• Average and highest PWM applied during last slip recovery event
• Throttle anticipation mode
• Average and highest PWM applied during last Throttle anticipation corrective action event
• Difference between front and rear propshaft RPM
• Adapt event counter
• Throttle position sensor percentage

Check the transfer case shift control module for DTC's. The transfer case shift control module is not a class 2 device. DTC's are displayed on the transfer case shift control switch. Refer to Diagnostic Trouble Code (DTC) Displaying .
Are any DTC's present?
Diagnostic Trouble Code (DTC) Displaying
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
TCCM Self-Test
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
If the TCCM failed the Self-Test, then test the following circuits.
• Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage
• Ground Circuit for ground
• Diagnostic enable circuit for an open or high resistance
• Transfer case shift control switch connector
If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .
DTC Displaying
Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List .
Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.
• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.
• This sequence will continue until PIN 13 on the DLC is no longer grounded.
• If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

Apr 15, 2017 | Cars & Trucks

1 Answer

It feels like my 4WD is trying to engage when I am driving down the road. a terrible grinding noise comes and goes in my font end. What could this be?

The encoder motor on the transfer case could be engaging slightly.A c0327 is usually set in the transfer case module.Replace the sensor in the encoder motor if this code is present.

Dec 02, 2010 | 2003 Chevrolet Silverado 1500

1 Answer

Just replaced my encoder motor, front actuator, and dash switch....altough the transfer case engages it won't stay in 4 wheel drive for long

you may have to replace your trasfer case control module its right under dash driver side easy to access mine just went out it was throwing c0359 code 4 low cirut and service four wheel drive would come on dash although the 4wd works great it just throws the code.

Jan 01, 2010 | 2003 GMC Sierra

2 Answers

My 1999 chevy silverado 1500 four wheel drive won't engage. The truck is in 2wd now. When I push 4wd hi or low, I can hear the actuator try to engage the four wheel drive. The four hi or low button will...

You probably have a bad encoder motor.It is located on the side of the transfer case on the drivers side.It is black.The other problem they had with these was the switch but you have already replaced this so your next thing is the encoder motor.Hope this helps.Good luck.

Dec 28, 2009 | 1999 Chevrolet Silverado 1500

2 Answers

Service 4WD Light comes on. What exactly do I need to do?

have a dealer read the codes from the atc module..if has code 327 it will need an encoder sensor replaced..if code 2735 it will need a switch replaced in dash..if code 306 check grounds under cab mount ..if grounds are good replace encoder motor

Dec 27, 2009 | 2004 Chevrolet Tahoe

1 Answer

4 Wheel drive not functional

There is a TSB on this problem: TSB #03-04-21-001C

Subject:4WD Switch Indicator Lights Flashing, 4WD Inoperative, DTCs C0327, P0500, P0836, P1875 Set (Replace Encoder Motor Sensor, Reprogram TCCM, Inspect Front Drive Axle Engagement Sleeve for Damage/Repair) #03-04-21-001D - (12/04/2003)

Models:2003 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2003 GMC Sierra, Yukon, Yukon XL
with 4WD and Electric Shift or Active Transfer Case (RPO NP1 or NP8)
You can also try removing the TREC fuse (engine fuse box) and reinstall after 30 seconds. Look up the TSB number I gave you and you'll find alot more information.

Dec 16, 2009 | 2003 Chevrolet Tahoe

1 Answer

Service four wheel drive

Without further diagnostics, it could be any # of causes, but these are notorious for bad conections at the transfer case encoder motor and /or the encoder motor itself.The motor,when replaced may need to be reprogramed.Be sure the switch and wiring are functioning properly as the encoder and/or related control module are pricy$$

Jan 10, 2009 | 2002 GMC Sierra

2 Answers

Service 4wd

If you had the switch and encoder motor replaced 5 months ago, then you have warranty. You need to return to the dealer and have them pull codes to see if it is the C0327 again. Some of these trucks also had grounding issues for the 4wd module. If it is the same c0327 code stay on them and make them confirm their original diagnosis.

Nov 23, 2008 | 2005 Chevrolet Silverado 1500HD

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