How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Billy Your Own Question

Billy
Billy, Chevrolet tecnician
Category: Chevy
Satisfied Customers: 510
Experience:  Over 25 years experience,GM grand master for 8 years,certified smog and government safety inspector
12771247
Type Your Chevy Question Here...
Billy is online now
A new question is answered every 9 seconds

Procedure in diagnosing trouble code P2771 4WD low circuit

Customer Question

Procedure in diagnosing trouble code P2771 4WD low circuit on a 2004 tahoe.
Submitted: 5 years ago.
Category: Chevy
Expert:  Billy replied 5 years ago.
Hello and welcome to just answer.

I will be sending you the complete diagnostic chart for the DTC P2771.
You can follow it step by step and it should lead you to the source of the malfunction.
I'm sending it in two installments.

If you feel my answer was helpful, please click the ACCEPT button. Feedback & Bonuses are always welcome.
Best regards,
Billy.


DTC P2771

Object Number:(NNN) NNN-NNNN Size: MF

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, short to ground or short to power in the 4WD low circuit, then DTC P2771 sets. DTC P2771 is a type B DTC.

Conditions for Running the DTC

No TP sensor DTCs P0122, or P0123.
No VSS assembly 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 N·m (40-400 lb ft).
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 100-3,000 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.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for a short to ground in the 4WD low signal circuit.

  2. This step tests for an open in the 4WD low signal circuit or a faulty transfer case control module.

Expert:  Billy replied 5 years ago.
If you feel my answer was helpful, please click the ACCEPT button. Feedback & Bonuses are always welcome.
Best regards,
Billy.

DTC P2771

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls - 4.8L, 5.3L and 6.0L

2

  1. Install a scan tool.
  2. Start the engine, parking brake disengaged.
  3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.

  4. Record the DTC Freeze Frame and Failure Records.
  5. Clear the DTC.
  6. Place the transmission in NEUTRAL.
  7. Select 4HI on the transfer case selector.
  8. Important: It may be necessary to drive the vehicle slightly forward to engage 4LO on the transfer case.

  9. Select 4LO on the transfer case selector.

Does the scan tool 4WD Low display Disabled when you select 4HI, then Enabled when you select 4LO?

--

Go to Intermittent Conditions in Engine Controls - 4.8L, 5.3L and 6.0L

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the transfer case control module connector.
  3. Turn ON the ignition, with the engine OFF.

Does the scan tool 4WD Low indicate Enabled?

--

Go to Step 6

Go to Step 4

4

  1. Connect C1-1 of the transfer case control module connector.
  2. Observe the scan tool 4WD Low.

Does the scan tool 4WD Low indicate Enabled when the 4WD low signal circuit, is grounded?

--

Go to Step 5

Go to Step 7

5

Replace the transfer case control module.

Did you complete the replacement?

--

Go to Step 9

--

6

Test the 4WD low signal circuit for a short to ground.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

7

Test the 4WD low signal circuit for an open.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

8

Replace the powertrain control module (PCM).

Did you complete the replacement?

--

Go to Step 9

--

9

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
  4. 3.1. Select 4LO on the transfer case selector.
    3.2. Drive the vehicle in D4.
    3.3. Verify that the speed ratio is 2.5-2.9 for 1.5 seconds.
    3.4. Select 2HI or 4HI on the transfer case selector.
    3.5. Drive the vehicle in D4 with the TCC ON.
    3.6. Verify that the speed ratio is 0.8-1.2 for 5 seconds.
  5. Select Specific DTC.
  6. Enter DTC P2771.

Has the test run and passed?

--

Go to Step 10

Go to Step 2

10

With the scan tool, observe the stored information, capture info, and DTC Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 4.8L, 5.3L and 6.0L

System OK

Customer: replied 5 years ago.
Condition is intermittent.
Expert:  Billy replied 5 years ago.
Hello again,

You will need inspect the wiring (gray/black) and all inputs to the pcm and transfer case control module. Unplug the connectors and check for corrosion and make sure the terminals are clean and tight.
Check the power and ground inputs to the modules. If all is well, then either keep on testing until it acts up or start replacing components. In this case I would start by replacing the transfer case control module first.

Remember

When the PCM detects a continuous open, short to ground or short to power in the 4WD low circuit, then DTC P2771 sets. So make sure the gray/black wire is not shorting out anywhere.


If you feel my answer was helpful, please click the ACCEPT button. Feedback & Bonuses are always welcome.
Best regards,
Billy.

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
< Last | Next >
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
< Last | Next >
  • http://ww2.justanswer.com/uploads/TI/tim37857/2011-10-28_23053_S6301814.64x64.JPG Tim's Auto Repair's Avatar

    Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
  • http://ww2.justanswer.com/uploads/DT/dt69nova/2012-6-15_234154_pic1.64x64.jpg Dave Nova's Avatar

    Dave Nova

    Chevrolet Technician

    Satisfied Customers:

    6870
    ASE Master Certification. GM World Class Certification
  • http://ww2.justanswer.com/uploads/ggrote1/2009-06-27_031011_me.jpg Gary's Avatar

    Gary

    Chevy Technician

    Satisfied Customers:

    5404
    15 years GM master tech
  • http://ww2.justanswer.com/uploads/testedtuff/2009-09-26_170108_pictures.jpg John's Avatar

    John

    Master A.S.E Automotive technician

    Satisfied Customers:

    4071
    A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
  • http://ww2.justanswer.com/uploads/RO/rodcuda/2011-7-25_224114_Donhoff1.64x64.JPG Neal's Avatar

    Neal

    Chevy Mechanic

    Satisfied Customers:

    2306
    Shop Owner and Mechanic on multiple makes.
  • http://ww2.justanswer.com/uploads/goodwrench9124/2008-11-09_220838_dscf0007.jpg goodwrench9124's Avatar

    goodwrench9124

    ASE Certified Technician

    Satisfied Customers:

    2041
    Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
  • http://ww2.justanswer.com/uploads/DR/drivefast1971/2012-1-12_172422_0009051tQKh.64x64.jpg Ron Z.'s Avatar

    Ron Z.

    - Chevy Tech -

    Satisfied Customers:

    1912
    18+yrs experience. State Inspector and Chevy Diagnostics