P2771
DTC P2771
Circuit Description
The four-wheel drive (4WD) low circuit consists of the powertrain control module (PCM), a transfer case control module and the circuit wiring. The transfer case control module controls the 4WD low signal on the low signal circuit. When the operator selects 4WD low, the transfer case control module grounds the signal circuit, and the 4WD low signal voltage on the circuit changes from ignition voltage to zero volts. The PCM then compensates for transfer case gear reduction in the transmission output shaft speed (OSS) sensor signal. The PCM uses the transmission OSS sensor signal to adjust shift points, line pressure and torque converter clutch (TCC) scheduling.
When the PCM detects a continuous open or short to ground in the 4WD low circuit, then DTC P2771 sets. 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
* No vehicle speed sensor (VSS) DTCs P0502 or P0503.
* No TCC solenoid valve DTC P2769 or P2770.
* No 1-2 shift solenoid (SS) valve DTCs P0751, P0973 or P0974.
* No 2-3 SS valve DTCs P0756, P0976 or P0977.
* No transmission fluid pressure (TFP) manual valve position switch DTC P1810, P1815 or P1816.
* No torque converter clutch (TCC) pulse width modulation (PWM) solenoid valve DTC P2763 or P2764.
* The engine speed is greater than 475 RPM for 5 seconds.
* The engine is not in fuel cutoff.
* The vehicle speed is greater than 2 km/h (1 mph).
* The throttle position (TP) angle is 5-100 percent.
* The engine torque is 95-675 N.m (70-295 lb ft).
* The gear range is D4.
* The shift solenoid performance counters are zero.
* The transmission fluid temperature (TFT) is 20-130°C (68-266°F).
Conditions for Setting the DTC
DTC P2771 sets if one of the following conditions occurs:
Condition 1
* The 4WD low switch is in 4WD low.
* The transfer case is not in 4WD low.
* The transfer case ratio is 0.95-1.05, the transfer case ratio is the engine speed divided by the transfer case output speed.
* All conditions are met for 5 seconds.
Condition 2
* The 4WD low switch is not in 4WD low.
* The transfer case is in 4WD low.
* The transfer case ratio is 2.65-2.73.
* All conditions are met for 5 seconds.
Action Taken When the DTC Sets
* The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* SERV 4WD message displays on the driver information center (DIC).
* The PCM commands a normal shift pattern, not a 4WD low shift pattern.
* The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
* The PCM stores DTC P2771 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC
* The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
* A scan tool can clear the MIL/DTC.
* The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
* The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. This step tests for a short to ground in the 4WD low signal circuit.
4. This step tests for an open in the 4WD low signal circuit or a faulty transfer case control module, active transfer case vehicles, or transfer case switch, non-active transfer case vehicles.
