Keeps blowing ATC 20amp fuse under hood

Tiny
BIGTDAN
  • MEMBER
  • 2000 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 224,000 MILES
In June 2019 4wd quit working. I replaced front actuator that did nothing. So I replaced transfer case shift motor the 4wd drive started working properly.
A month or so later the atc under the hood blew. Replaced fuse worked for awhile.
Now it blows the fuse all the time some times it work for a day or two other times it blows as soon as I turn the key on.
I traced all the wires and can not find any obvious shorts in the wiring harness.
I got the codes scanned 12-06-2019 and came up with 4
c0327
c0387
c0323
u1096
I am lost and looking for any help I can get. I have a new TCCM but not thrilled in putting in a $250.00 part if this is not going to fix my problem.
Tuesday, December 10th, 2019 AT 3:04 PM

16 Replies

Tiny
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Good evening,

What fuse number is the one that is failing? ATC is the power for the encoder motor. Disconnect the motor and see if the fuse still fails.

Roy

C0327

Circuit Description
The transfer case encoder is a switch that converts a shaft position, representing a mode or range position, into electrical signals for use by the transfer case shift control module. The encoder houses 4 Hall effect sensors that are used for channels P, A, B, and C. These sensors provide a path to ground, when a magnet, (part of the Motor Encoder), passes over them.
The transfer case shift control module supplies an 8 V reference and a ground circuit for the encoder hall effect sensors to function.
The transfer case shift control module supplies current limited 5 V on all the channels, thus as these channels are pulled to ground, the module can interpret the location of the transfer case shift position.
This DTC detects an open, short to ground, or a short to voltage (12 V) in the Encoder Feed Circuit, an open in the Signal Ground Circuit, an open, short to ground, or short to voltage (12 V) in the Encoder channel circuits.

Conditions for Setting the DTC
The transfer case shift control module reads back all high or low voltage on the Encoder channel circuits.

Action Taken When the DTC Sets
All motor activity will stop and the Transfer Case Lock engaged.
A default rail to rail shift may be allowed, (toggle between 4H and 2H).
The SERVICE indicator (4WD/AWD) lamp will be latched on for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
The transfer case shift control module will clear the DTC if the condition for setting the DTC no longer exists.
A history DTC will clear after 100 consecutive ignition cycles without a fault present.
History DTCs can be cleared using a scan tool.

Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
2. Tests the operation of the system.
3. Helps determine if the encoder has supply voltage.
4. Tests the encoder channels for proper reference voltage.
5. Tests the encoder channels for an open or a short to power.
6. Measures the voltage from the Encoder Feed circuit to the Encoder Signal Ground circuit.
7. Tests for two or more encoder channels shorted together.
8. Bypasses the encoder and tests each encoder channel individually. Helps isolate between encoder and module malfunctions.
9. Tests the suspect encoder channel(s) for an open.
10. Tests the encoder channels for proper reference voltage.
11. Helps determine if the Encoder Signal Ground circuit is shorted to voltage.
12. Tests the Encoder Feed circuit for a short to voltage.
13. Tests the Encoder Signal Ground circuit for high resistance or an open.
14. Tests the Encoder Feed circuit for an open.
15. Repairs shorted condition between the circuits that were simultaneously turned ON in Step 6.
16. Tests the encoder channel(s) that are not within the specified range previously tested in Step 9 for an open circuit.

C0387

Circuit Description
The transfer case encoder is a switch that converts a shaft position, representing a mode or range position, into electrical signals for use by the transfer case shift control module. The encoder houses 4 Hall effect sensors that are used for channels P, A, B, and C. These sensors provide a path to ground, when a magnet, (part of the Motor Encoder), passes over them.
The transfer case shift control module supplies an 8 V reference and a ground circuit for the encoder hall effect sensors to function.
The transfer case shift control module supplies current limited 5 V on all the channels, thus as these channels are pulled to ground, the module can interpret the location of the transfer case shift position.
This DTC detects that the transfer case is unable to successfully complete a shift to a requested mode or range.

Conditions for Setting the DTC
The transfer case shift control module will test the motor circuits and determine that there are no motor circuit faults existing.
The transfer case shift control module has attempted to shift to a requested mode/range and has failed to reach the desired position.
The transfer case shift control module has performed a default shift to 4LO or 4HI.

Action Taken When the DTC Sets
The SERVICE indicator (AWD/4WD) lamp will be latched on for the remainder of the current ignition cycle.
All shifting will be disabled.
The range/mode lights will be disabled
The next ignition cycle, the transfer case shift control module will power-up as if the 4HI was the mode present when the ATC was powered down.

Conditions for Clearing the DTC
The transfer case shift control module will clear the DTC if the condition for setting the DTC no longer exists.
A history DTC will clear after 100 consecutive ignition cycles without a fault present.
History DTCs can be cleared using a scan tool.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. Tests whether the transfer case shift control module is sensing any change in all of the encoder channels.
3. Helps determine whether the shift is prevented due to a mechanical fault.
4. Tests whether the transfer case shift control module is sensing any change in any of the encoder channels.
5. Tests if proper reference voltage is being supplied to the encoder from the suspect circuit.
6. Helps determine whether a short between 2 or more encoder circuits exist.
7. Tests the suspect encoder circuit for the module's ability to sense the circuit going low.
8. Helps determine whether the shift is prevented due to a mechanical fault.
9. Tests for the electrical energizing of the encoder motor.
10. Tests the suspect circuit(s) for an open or a short to power.
11. Tests for short between the suspect circuits.
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Tuesday, December 10th, 2019 AT 3:51 PM
Tiny
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It's the 20 amp atc under the hood it does not have a number. If I unplug the encoder motor what should I do to test and see if the fuse blows? I unplugged it last week cycled threw the 4hi 4 low 2 hi and auto it did no blow the fuse but I did not drive it. Then I plugged it back in uses 4 hi twice then the third time in blew atc fuse.
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Tuesday, December 10th, 2019 AT 4:09 PM
Tiny
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Yes, unplug it and then install the fuse and see if it fails.

If it does, then you have a wiring issue between the fuse block and the motor. If it does not fail, the motor is drawing too much amperage and causing the fuse to fail.

Roy
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Tuesday, December 10th, 2019 AT 4:13 PM
Tiny
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Okay. I have read a lot of different post about this. Some people are replacing the transfer case control module. It's the only part I have not replaced. I read that even new encoder motors fail. I know when I replaced the encoder motor 6 months ago it worked for a while before it blew atc fuse. Have you heard of a lot of new encoder motors going bad?
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Tuesday, December 10th, 2019 AT 4:22 PM
Tiny
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I have put brand new parts on that were defective out of the box.

Did you do the test I suggested?

Roy
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Tuesday, December 10th, 2019 AT 4:24 PM
Tiny
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I will retest in the morning it's dark outside and a pain to unplug the encoder motor.
Last week when I unplugged it the dude did not blow. I cycled threw auto 2hi 4hi and 4low several times and it did not blow.
I will try again in the morning.
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Tuesday, December 10th, 2019 AT 4:33 PM
Tiny
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Sounds like a plan.

Roy
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Tuesday, December 10th, 2019 AT 4:43 PM
Tiny
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Okay, there are 2 plugs on encoder motor. The one that goes to the bottom and 1 that goes to in the side near the top. I unplugged the wires that run to the bottom and fuse has not blown yet. Is that the right wire?
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Wednesday, December 11th, 2019 AT 9:28 AM
Tiny
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What color are the wires?

Roy
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Wednesday, December 11th, 2019 AT 12:07 PM
Tiny
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The 4 wires that run to bottom of transfer case that I have unplugged are red, black, orange and yellow.
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Wednesday, December 11th, 2019 AT 12:31 PM
Tiny
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The plug that I did not unplug are
Brown with white stripe.
Black with withe stripe.
Blue with white stripe.
Red with white stripe.
Green
Yellow with black stripe
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Wednesday, December 11th, 2019 AT 12:39 PM
Tiny
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Yes, that is the correct plug.

I would drive it around to be sure the fuse does not fail.

Let me know how you make out.

Roy
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Wednesday, December 11th, 2019 AT 12:49 PM
Tiny
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Okay, it has been a few days and no blown fuse.
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Monday, December 16th, 2019 AT 10:37 AM
Tiny
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Okay, then the encoder motor is causing the fuse to fail.

I would replace the encoder motor.

Roy
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Monday, December 16th, 2019 AT 12:07 PM
Tiny
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Okay, I replaced encoder motor. Worked for about a week then blew fuse again. For the week it worked I used 4wd a dozen times and every thing worked great. Friday put it in 4wd blew the fuse. Do you think it could be transfer-case control module?
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Monday, December 30th, 2019 AT 3:56 PM
Tiny
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It sounds like the motor is pulling too much current to operate. That would make me think the it could be the transfer case itself. Something may be binding up and causing the motor to draw more current than the fuse allows.

Roy
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Monday, December 30th, 2019 AT 4:21 PM

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