GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 LaCrosse 🢒 Engine 🢒 Engine Controls and Fuel - 3.8L 🢒 DTC P0506 or P0507

Diagnostic Instructions
    •  Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0506: Idle Speed Low

DTC P0507:  Idle Speed High

Circuit/System Description

The throttle actuator control (TAC) motor is controlled by the TAC module using various inputs from the powertrain control module (PCM) which are communicated across serial data. The DC motor located in the throttle body drives the throttle plate. In order to decrease idle speed, the TAC module commands the throttle closed, reducing air flow into the engine. In order to increase idle speed, the TAC module commands the throttle plate open, allowing more air to pass the throttle plate. If actual idle RPM does not match the desired idle RPM within a calibrated time, DTC P0506 or P0507 sets.

Conditions for Running the DTC
    • DTCs P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0125, P0128, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0300, P0401, P0404, P0405, P0443, P0496, P0502-if applicable, P0503-if applicable, P1106, P1107, P1111, P1112, P1114, P1115, P1404, P1516, P2101, P2107, P2108, P2119, P2120, P2125, P2135, P2138, U0107 are not set.
    • DTCs P0136, P0401 and P0420 have passed.
    • The engine is idling for more than 1 second.
    • The engine coolant temperature (ECT) is more than -40°C (-40°F).
    • The intake air temperature (IAT) is more than -40°C (-40°F).
    • The barometric pressure (BARO) is more than 60 kPa.
    • The system voltage is between 11-18 volts.
    • The vehicle speed is less than 4.8 km/h (3 mph).
    • The throttle angel is less than 0.25 percent.
    • DTC P0506 and P0507 run continuously when the above conditions are met.

Conditions for Setting the DTC

P0506

    • The difference between the actual and desired idle RPM exceeds a calibrated limit. This limit varies from 300 RPM at -40°C (-40°F) to 100 RPM at 152°C (305°F) based on engine coolant temperature.
    •  The above condition is present for 8 seconds in order for the test to fail. Four tests must fail in order to set this DTC. The vehicle must exit condition for running between each test.

P0507

    • The difference between the actual and desired idle RPM exceeds a calibrated limit. This limit varies from 300 RPM at -40°C (-40°F) to 175 RPM at 152°C (305°F) based on ECT.
    • The above conditions must be present for 8 seconds in order for the test to fail. Four tests must fail in order to set this DTC. The vehicle must exit conditions for running between each test.

Action Taken When the DTC Sets
    • DTC P0506 and P0507 are Type B DTCs.
    • The control module commands the TAC system to operate in the Reduced Engine Power mode.

Conditions for Clearing the MIL/DTC

DTC P0506 and P0507 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Throttle Actuator Control (TAC) System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Using a scan tool, compare the desired engine idle speed to the actual engine idle speed.
    2. ⇒Actual engine idle speed should be no greater than 175 RPM below desired.
    ⇒Actual engine idle speed should be no greater than 175 RPM above desired.
  2. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing
  1. Observe the DTC information on the scan tool.
    2. ⇒If there are any other DTCs set, diagnose those first.
  2. Inspect for any condition that can reduce idle speed by increasing engine load.
    3. • Incorrect torque converter clutch (TCC) operation
    • Accessories that require additional torque to operate
    • Excessive deposits in the throttle body
    • Restricted exhaust
    • Mechanical conditions that limit engine speed
         ⇒Repair any conditions, if necessary.
  3. Inspect for the following conditions:
    4. • Vacuum leaks
    • A faulty positive crankcase ventilation (PCV) valve

Repair Verification

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.