Circuit Description
The 4WD low signal circuit is used to notify the transmission control module (TCM) that the vehicle is in 4WD low range.
DTC P2771 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2771 Four Wheel Drive (4WD) Low Switch Circuit
Conditions for Running the DTC
| • | DTCs P0721 and P0722 are not active. |
| • | The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts. |
| • | Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds. |
| • | Output speed is greater than 60 RPM. |
| • | Transmission fluid temperature (TFT) is 20-130°C (68-266°F). |
| • | The shift is complete and NEUTRAL range is not selected. |
Conditions for Setting the DTC
DTC P2771 sets when one of the following conditions occur:
| • | The transfer case switch indicates high range, and the calculated range is low range for 5 seconds or greater. |
| • | The transfer case switch indicates low range, and the calculated range is high range for 5 seconds or greater. |
Action Taken When the DTC Sets
| • | The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. |
| • | DTC 2771 will be stored in TCM history. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
| • | Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions: |
| - | A bent terminal |
| - | A backed-out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| • | When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. |
| • | You may have to drive the vehicle in order to experience a condition. |
| • | Inspect for any transmission DTCs that may have set again. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the status of the 4WD Low switch.
-
This step tests for a 4WD switch failure to ground.
-
This step tests for a short in the wiring harness.
-
This step tests for a 4WD switch failure to an open state.
-
This step tests for an open in the wiring harness.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. Does the scan tool indicate 4WD low status as NO when 4HI is selected, and YES when 4LO is selected? | -- | Go to Diagnostic Aids | Go to Step 3 | |
Select 4HI followed by 4LO using the transfer case selector. Does the scan tool indicate 4WD low status as YES for both selector positions? | -- | Go to Step 4 | Go to Step 9 | |
Remove the connector at the transfer case selector. Does the scan tool indicate 4WD low status as YES? | -- | Go to Step 5 | Go to Step 7 | |
5 | Inspect 4WD Low signal circuit for a short to ground. Did you find a condition? | -- | Go to Step 6 | Go to Step 15 |
6 | Inspect and repair the short to ground in 4WD Low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
7 | Inspect the transfer case switch for proper operation or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find a condition? | -- | Go to Step 8 | Go to Step 15 |
8 | Replace the transfer case switch. Refer to Transfer Case Shift Control Module Replacement in Transfer Case - NVG 263 - NP1. Did you complete the replacement? | -- | Go to Step 16 | -- |
Using the transfer case selector, select 4HI followed by 4LO. Does the scan tool indicate 4WD Low status as NO for both selector positions? | -- | Go to Step 10 | Go to Step 15 | |
Does the scan tool indicate 4WD low status as NO? | -- | Go to Step 11 | Go to Step 13 | |
11 | Inspect the short to ground in the brake switch signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find a condition? | -- | Go to Step 12 | Go to Step 15 |
12 | Repair the open condition in the 4WD Low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
13 | Inspect the transfer case switch for an open condition. Did you find an open condition? | -- | Go to Step 14 | Go to Step 15 |
14 | Replace the transfer case switch. Refer to Transfer Case Shift Control Module Replacement in Transfer Case - NVG 263 -NP1. Did you complete the replacement? | -- | Go to Step 16 | -- |
15 |
Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Replace the TCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | -- |
16 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK | Go to Step 1 |
