I have an 05 avalanche with 142xxx miles on it, all stock. Today for the second time it engaged 4wd low range by itself when I started it to leave a parking lot. It happened one other time, but I thought I may have hit the button by mistake when my hand slipped off the steering wheel. I didn't hear any bad noises. I noticed it felt strange when I tried to go, and the service 4wd light came on. It would not shift into 2wd hi until I restarted the truck and put it in neutral. It has a po327 code, but I didn't know it would make it shift by itself. I tried to buy the sensor to fix the code, but the gm dealer looked at me like an idiot. so I gave up on them, and havn't had time to go to another. Any Ideas?
Thanks
Eric

 

P0327 is a Knock sensor code- not related to the T-case operation.

Part 1:

DTC C0327

Circuit Description

The transfer case encoder is an analog sensor that returns a signal that represents the physical position of the transfer case sector shaft. This signal represents the mode or position that the transfer case is currently in. This sensor is made up of the following 3 circuits:
• 5-volt reference circuit • Encoder signal circuit • Encoder low reference circuit
This DTC detects an out of range reading from the encoder signal, a short to voltage on the 5-volt reference circuit.

DTC Descriptor

This diagnostic procedure supports the following DTC:
DTC C0327 Encoder Circuit Malfunction

Conditions for Setting the DTC

The transfer case shift control module has a predefined range, 0.5-4.5 volts, in which the encoder feed back should stay within. The DTC sets if the encoder signal feed back falls out of this range.

Action Taken When the DTC Sets

• All motor activity stops and the transfer case lock engages. • The SERVICE 4WD indicator remains illuminated 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 is not currently present. • 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. This step checks for a voltage reading on the scan tool.


3. This step tests the encoder circuit for a current malfunction.

4. This step tests for an internal encoder malfunction which is present only in certain areas of the encoder sensor.

5. This step tests for proper reference voltage at the encoder.

6. This step tests the 5-volt reference circuit for proper voltage when the low reference circuit is used as a ground.

8. This step tests the 5-volt reference encoder circuit for a short to voltage, short to ground, an open or high resistance.

9. After determining if the reference voltage measured in Step 4 is correct, Step 6 reviews the reading originally measured in Step 3 to see if it is higher or lower than what is expected. This step helps determine whether the encoder signal circuit is being pulled high or low.

10. This step tests the encoder signal circuit and the encoder low reference circuit for a short to voltage.

11. This step helps determine a faulty encoder.

12. This step tests the encoder signal circuit and the encoder low reference circuit for an open or a short to ground.

 

Part 2:

Step
Action
Values
Yes
No

1 Did you perform the Diagnostic System Check - Vehicle?
--
Go to Step 2
Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2

1. Install a scan tool. Turn the ignition ON with the engine OFF.
2. With a scan tool, observe the Encoder supply and return voltage parameters.

Are the voltage parameters displayed?

--
Go to Step 3
Go to Step 5
3

1. Install a scan tool. Start the engine. Set the park brake. Place the transmission in Neutral. With a scan tool, observe the Encoder Return Voltage parameter.
2. Select each of the mode positions.

Does the voltage reading stay within the specified values?

0.5-4.5 V
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
Go to Step 4
4
Does the voltage reading stay within the specified values at any position?
0.5-4.5 V
Go to Step 13
Go to Step 5
5

1. Turn the ignition OFF. Disconnect the encoder motor. Turn the ignition ON with the engine OFF.
2. Measure the voltage from the 5-volt reference encoder circuit to ground at the transfer case shift control module side of the harness.

Does the voltage measure within the specified values?

4.8-5.2 V
Go to Step 6
Go to Step 8
6
Test the low reference circuit by jumping from the 5-volt reference circuit pin A to the low reference circuit pin C at the encoder pigtail on the module side of the harness.
Does the voltage reading stay within the specified values?
4.8-5.2 V
Go to Step 9
Go to Step 7
7
Test the low reference circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 15
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
8
Test the 5-volt reference circuit for a short to voltage, a short to ground, an open, or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 15
Go to Step 14
9
Was the voltage reading measured in Step 4 greater than 5.2 volts?
--
Go to Step 10
Go to Step 11
10
Test the encoder signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 15
Go to Step 14
11

1. Install a scan tool. Turn the ignition ON with the engine OFF. Using a fused jumper, back probe between the 5-volt reference encoder circuit and encoder signal circuit at the transfer case shift control module side of the harness.
2. With a scan tool, observe the Encoder Return Voltage parameter.

Is the encoder return voltage display within the specified values?

4.8-5.2 V
Go to Step 13
Go to Step 12
12
Test the encoder signal circuit and the encoder low reference circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 15
Go to Step 14
13
Replace the encoder sensor. Refer to Encoder Motor Sensor Replacement .
Did you complete the repair?
--
Go to Step 15
--
14
Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
Did you complete the repair?
--
Go to Step 15
--



15

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC set?

 

CO327.....thats what i meant, I was having a bad day. Thanks for all the info, I know what I'm doing tomorow.