4L60-E/4L65-E/4L70-E - Automatic Transmission
DTC P2771
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P2771
-
Four Wheel Drive (4WD) Low Switch Circuit
Diagnostic Fault Information
Circuit/System Description
The Replicated TOS Signal circuit consists of the engine control module (ECM), the transmission control module (TCM) and a communication line, replicated TOS signal, between the two modules. The transfer case control module (TCCM) controls the 4WD low function. When the operator selects 4WD low, the TCCM commands the encoder motor to change ranges to 4WD low. The TCCM sends a message to the TCM. The TCM sends a message to the ECM over the Replicated TOS Signal circuit notifying the ECM that the output speed will be changing. The ECM then compensates for transfer case gear reduction in the transmission output shaft speed (OSS) sensor signal. The ECM uses the transmission OSS sensor signal to adjust shift points, line pressure and torque converter clutch (TCC) scheduling.
Conditions for Running the DTC
* No throttle position (TP) sensor DTCs P0122, or P0123.
* No OSS assembly DTCs P0722 or P0723.
* No cam or crank sensor DTCs.
* The system voltage is 8-18 volts.
* The engine speed is 1,000-5,500 RPM for at least 30 seconds.
* The vehicle speed 5 km/h (3 mph).
* The TP angle 5 percent.
* The gear range is not PARK, NEUTRAL or REVERSE.
* The TFT is -20 to +130°C (-4 to +266°F).
Conditions for Setting the DTC
The TCCM calculated transfer case ratio is not consistent with the position of the transfer case shift control switch.
Condition 1
The transfer case shift control switch (TCSCS) indicates 4WD HIGH and the TCCM calculated transfer case range indicates 4WD LOW, for 2 seconds.
OR
Condition 2
The TCSCS indicates 4WD LOW range and the TCCM calculated transfer case range indicates 4WD HIGH, for 2 seconds.
Action Taken When the DTC Sets
* DTC P2771 is a Type B DTC.
* The ECM commands a normal shift pattern, not a 4WD low shift pattern.
Conditions for Clearing the DTC
DTC P2771 is a Type B DTC.
Diagnostic Aids
1. A malfunctioning speed sensor could cause DTC P2771 to set.
* Verify that the input speed sensor (ISS) and the OSS are functioning properly.
* In 3rd gear at approximately 64 km/h (40 mph), command TCC ON. If functioning properly the OSS will track ISS and the engine RPM. If not refer to DTC P0716 for the ISS and DTC P0723 for the OSS.
* If the speed sensors pass testing, refer to Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections.
2. The scan tool 4WD Low display is not under the Transfer Case Control Module/Data Display. It can be found in the following modules:
* Transmission Control Module
B Data Display B Transmission Data B 4WD Low Signal
* Engine Control Module
B Data Display B Auto. Transmission Data B 4WD Low Signal
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics 4L60-E/4L65-E/4L70-E - Automatic Transmission
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
Description and Operation
Transmission General Information Transmission General Information
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Transmission Control Module Scan Tool Information (Allison) Scan Tool Testing and ProceduresTransmission Control Module Scan Tool Information (4L60-E) Scan Tool Testing and ProceduresTransmission Control Module Scan Tool Information (2ML70) Scan Tool Testing and ProceduresTransmission Control Module Scan Tool Information (6L45/6L50/6L80/6L90) Scan Tool Testing and Procedures
Special Tools
J 35616 - GM-Approved Terminal Test Kit
Circuit/System Verification
Note:
It may be necessary to drive the vehicle slightly forward to engage 4LO on the transfer case.
1. Key ON. Engine OFF.
2. Parking brake ON. Transmission in Neutral.
3. Using the transfer case data display functionality of the scan tool, verify that the "Mode Switch Selected", "Transfer Case Position" and corresponding "Indicator Light" parameters all match when using the TCSCS to change modes.
• If the scan tool indicates different than stated, Refer to Symptoms - Transfer Case Symptoms - Transfer Case , Symptoms - Transfer Case Symptoms - Transfer Case or Symptoms - Transfer Case Symptoms - Transfer Case.
4. Using the TCM - transmission data display functionality of the scan tool, verify that the "4WD Low parameter", reads Enabled/Disabled when using the TCSCS to go In/Out of 4WD Low.
• If the parameter does not perform as specified, suspect a Replicated TOS Signal circuit or TCM condition.
5. Using the ECM - auto. transmission data display functionality of the scan tool, verify that the "4WD Low parameter", reads Enabled/Disabled when using the TCSCS to go In/Out of 4WD Low.
• If the parameter does not perform as specified, suspect a Replicated TOS Signal circuit or ECM condition.
Circuit/System Testing
1. If any other DTCs are set, diagnose them first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle. Excessive slip in the transmission or transfer case or faulty speed sensors can cause DTC P2771 to set.
2. Key Off. Disconnect the X1 connector at the ECM.
3. Key ON. Engine OFF.
Note:
When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J 35616 - test kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.
4. Test for B+ (+0.0/-1.5 V) between the Replicated TOS Signal circuit, ECM X1 Pin 71, and the ECM ground circuit, ECM X1 pin 73.
• If the voltage is less than the specified range, test the Replicated TOS Signal circuit for an open/high resistance or short to ground. If all circuits and connections test normal, replace the TCM.
5. Test for greater than 100 ohms between the Replicated TOS Signal circuit, ECM X1 Pin 71, and all other pins of the ECM X1.
• If less than the specified range, test the affected circuits for a shorted together condition.
6. Key Off. Disconnect the X1 connector at the TCM.
7. Test for less than 1 ohms between the Replicated TOS Signal circuit, ECM X1 Pin 71, and the Replicated TOS Signal circuit, TCM X1 Pin 5.
• If greater than the specified value, test the affected circuit for a open/high resistance condition.
8. Connect the X1 connector at the ECM. Key ON. Engine OFF.
9. Test for 2.0-3.0 V between the Replicated TOS Signal circuit, TCM X1 Pin 5, and the TCM ground circuit, TCM X1 pin 49.
• If the voltage is greater than the specified range, test the Replicated TOS Signal circuit for a short to B+. If all circuits and connections test normal, replace the ECM.
• If the voltage is less than the specified range, test the Replicated TOS Signal circuit for an open/high resistance or short to ground. If all circuits and connections test normal, replace the ECM.
10. Test for greater than 100 ohms between the Replicated TOS Signal circuit, TCM X1 Pin 5, and all other pins of the ECM X1.
• If less than the specified range, test the affected circuits for a shorted together condition.
11. If all circuits and connections test normal go to Symptoms - Transfer Case Symptoms - Transfer Case , Symptoms - Transfer Case Symptoms - Transfer Case or Symptoms - Transfer Case Symptoms - Transfer Case.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
Control Module References Control Module References for replacement, setup, and programming