2009 siverado rpm issues

crappieman · September 7, 2021

hi everyone, new to this site, i have a 2009 chevy silverado 1500 5.3l v8 auto, starts fine, idle fine in park, problem is when driving rpms will spike

set cruise at 60mph, everything fine for about 6 miles then rpms just shot up over 3000, took it out of cruise but still had issue, got it back home

having to go approx. 45mph, every time i gave it gas rpms would go wild, no codes or check engine light appears, took it for another ride to see

if it would repeat issue and now just accelerating causes rpms to surge, would like any input on what the issue could be

redvett · September 7, 2021

Have you checked trans oil level.

crappieman · September 7, 2021

thanks, checked it after i posted, it is low , waiting for wife to bring some home

will let you know, thanks again

CamGTP · September 8, 2021

Sounds like it's slipping. If it's been low for a long time, then the damage could already be done so just be warned of that.

crappieman · September 12, 2021

finally got back to checking out truck, engine light now on, p2771 code on, says something about 4wd low switch circuit, have no idea what to check, just want to eliminate what i can before taking to mechanic, any help would be appreciated

swathdiver · September 14, 2021

On 9/12/2021 at 6:00 PM, crappieman said:

finally got back to checking out truck, engine light now on, p2771 code on, says something about 4wd low switch circuit, have no idea what to check, just want to eliminate what i can before taking to mechanic, any help would be appreciated

Your rpms problem to me seems like a vacuum leak or bad throttle.

From the shop manual:

DTC Descriptor
DTC P2771
Four Wheel Drive (4WD) Low Switch Circuit
Circuit/System Description

The four wheel drive (4WD) low circuit consists of the engine control module (ECM), a transfer case control module and the circuit wiring. The transfer case control module controls the 4WD 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 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 9-18 volts.
The engine speed is 1,000-5,500 RPM for at least 30 seconds.
The vehicle speed is at least 40 km/h (25 mph).
The TP angle is 5-40 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

Condition 1
The 4WD low switch is not in 4WD low, open/12 volts.
The Transfer Case Ratio is 2.64-2.9 for 2 seconds.
Both conditions must be met twice.
Condition 2
The 4WD low switch is in 4WD low.
The Transfer Case Ratio is 0.8-1.75 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

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 (See: Testing and Inspection\Component Tests and General Diagnostics).
Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (See: Transmission and Drivetrain\Automatic Transmission/Transaxle\Diagrams\Electrical)
Connector End View Reference

Component Connector End Views (See: Diagrams\Connector Views)
Description and Operation

Transmission General Information (See: Transmission and Drivetrain\Automatic Transmission/Transaxle\Description and Operation\4L60-E/4L65-E/4L70-E Automatic Transmission\Transmission General Information)
Electrical Information Reference

Circuit Testing (See: Testing and Inspection\Component Tests and General Diagnostics)
Connector Repairs (See: Testing and Inspection\Component Tests and General Diagnostics)
Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection\Component Tests and General Diagnostics)
Wiring Repairs (See: Testing and Inspection\Component Tests and General Diagnostics)
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (See: Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Transmission Control Module Scan Tool Information (4L60-E) (See: Testing and Inspection\Scan Tool Testing and Procedures\Transmission Control Module Scan Tool Information (4L60-E))Transmission Control Module Scan Tool Information (6L50/6L80/6L90) (See: Testing and Inspection\Scan Tool Testing and Procedures\Transmission Control Module Scan Tool Information (6L50/6L80/6L90))

Special Tools

J 35616 GM-Approved Terminal Test Kit

Circuit/System Verification

Important: It may be necessary to drive the vehicle slightly forward to engage 4LO on the transfer case.

Verify the scan tool displays Disabled when you select 4HI and Enabled when you select 4LO.

Circuit/System Testing

Remove connector from the transfer case control module. With ignition ON and engine OFF, observe with the scan tool the 4WD Low parameter.
¤   If the scan tool indicates Enabled, test the 4WD Low signal circuit for a short to ground.
Using the J 35616 GM-approved terminal test kit, install a fused jumper between the 4WD low signal circuit and ground at the transfer case control module connector.
¤   If the scan tool 4WD Low parameter indicates Enabled when grounded, replace the transfer case control module.
Test the 4WD Low signal circuit for an open.
¤   Fix the open in the 4WD Low circuit.
Replace the ECM.
Component Testing

Verify the 4WD Low parameter on scan tool while cycling the 4WD Low switch.