P2771 Code On My 04 Silver

[jmp2204]

yesterday i start my truck up and it is in 4wd auto (lit up on the push button on it's own) it acted like it was in 4wd though (binding around corners) .started a thread in another section on here.(fullsize etc...)...today it was back in 2wd and then in showed itself in neutral on the push button,then tonight on my way home it luminated 4wd (but wasn't in it) buddy of mine (is a chrysler tech )came over(with a spare known to be good push button switch and his obd2) we got code p2771 . he crawled under the truck and could hear the motor trying to function (didn't know if it sounded right) but it would not complete a switch to anything other than 2wd(with either switch, his or mine) if the encoder motor is faulty would it still make noise? i read something about the transfer case shift control module is that more likely if the motor is still sounding? and what about the programming? I really appreciate any help with this thanks for your time(i am a former tech that left the trade in the 80's)

[matthuber1]

P2771 is '4wd low switch circuit'

 

Circuit Description with 4L60-E / 4L65-E Automatic Transmission

For vehicles equipped with an active transfer case, 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.

 

For vehicles not equipped with an active transfer case, the 4WD low circuit consists of the PCM, a transfer case switch and the circuit wiring. The transfer case switch controls the 4WD low signal on the signal circuit. When the operator selects 4WD low, the transfer case switch closes and the 4WD low signal voltage on the signal 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 TCC scheduling.

 

When the PCM detects a continuous open, short to ground or short to voltage 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 TP sensor DTCs P0122, or P0123.
  
• No VSS DTCs P0502 or P0503.
  
• No TCC solenoid valve DTC P0740.
  
• No TCC stuck ON DTC P0742.
  
• No 1-2 SS valve DTCs P0751 or P0753.
  
• No 2-3 SS valve DTCs P0756 or P0758.
  
• No TFP manual valve position switch DTC P1810.
  
• No TCC PWM solenoid valve DTC P2761.
  
• The engine speed is greater than 450 RPM for 5 seconds.
  
• The engine is not in fuel cutoff.
  
• The vehicle speed is greater than 11 km/h (7 mph) .
  
• The TP angle is 17-50 percent.
  
• The engine torque is 54 - 542 Nm (40 - 400 ft. lbs.) .
  
• The engine vacuum is 0-105 kPa (0-15 psi) .
  
• The gear range is D4.
  
• The shift solenoid performance counters are zero.
  
• The 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 TCC slip speed is -3,000 to -50 RPM.
  
• The transfer case ratio is 0.08-1.2, 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 TCC is commanded ON.
  
• The TCC slip speed is 100 to 3,000 RPM.
  
• The transfer case ratio is 2.5-2.9.
  
• All conditions are met for 10 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.
  
• 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.
  

 

 

 

So... it seems that if the switch set to 4wd low and the t case is not in 4wd low, or vise versa you will get the code... seems like it could be the encoder?

[jmp2204]

P2771 is '4wd low switch circuit'

 

Circuit Description with 4L60-E / 4L65-E Automatic Transmission

For vehicles equipped with an active transfer case, 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.

 

For vehicles not equipped with an active transfer case, the 4WD low circuit consists of the PCM, a transfer case switch and the circuit wiring. The transfer case switch controls the 4WD low signal on the signal circuit. When the operator selects 4WD low, the transfer case switch closes and the 4WD low signal voltage on the signal 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 TCC scheduling.

 

When the PCM detects a continuous open, short to ground or short to voltage 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 TP sensor DTCs P0122, or P0123.

   

• No VSS DTCs P0502 or P0503.

   

• No TCC solenoid valve DTC P0740.

   

• No TCC stuck ON DTC P0742.

   

• No 1-2 SS valve DTCs P0751 or P0753.

   

• No 2-3 SS valve DTCs P0756 or P0758.

   

• No TFP manual valve position switch DTC P1810.

   

• No TCC PWM solenoid valve DTC P2761.

   

• The engine speed is greater than 450 RPM for 5 seconds.

   

• The engine is not in fuel cutoff.

   

• The vehicle speed is greater than 11 km/h (7 mph) .

   

• The TP angle is 17-50 percent.

   

• The engine torque is 54 - 542 Nm (40 - 400 ft. lbs.) .

   

• The engine vacuum is 0-105 kPa (0-15 psi) .

   

• The gear range is D4.

   

• The shift solenoid performance counters are zero.

   

• The 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 TCC slip speed is -3,000 to -50 RPM.

   

• The transfer case ratio is 0.08-1.2, 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 TCC is commanded ON.

   

• The TCC slip speed is 100 to 3,000 RPM.

   

• The transfer case ratio is 2.5-2.9.

   

• All conditions are met for 10 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.

   

• 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.

   

 

 

 

So... it seems that if the switch set to 4wd low and the t case is not in 4wd low, or vise versa you will get the code... seems like it could be the encoder?

hhhmmm now i'm confused LOL ,i'll have to read that again! thanks for the info!!!! btw great link!

[jmp2204]

Tip we got from a gm tech also on these trucks is corroded wires .(i am in Ontario Canada where in the winter they put alot of salt/sand on the roads to melt ice/snow)After alot of wire tracing we found the problem.Under the hood ,(the shroud around the fuse/relay panel) one of the harnessess was rubbing on the shroud and i had some open and corroded wires ,fixed them up and problem solved!(we rerouted the harness also) thanks for the input people~