GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls and Fuel - 7.8L (LF8) 🢒 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 engine control module (ECM) adjusts the fuel delivery in order to control crankshaft speed at idle. The ECM monitors the engine speed and will detect an out of range idle speed for the amount of fuel that is delivered.

Conditions for Running

P0506

    • DTCs P0117, P0118, P0126, P0335, P0336, P0500, P0507, P0602, P0652, P0653, P1125, P1293, P2146, P2147, P2148, P2150, P2151, and P268A are not set.
    • The idle mode is active.
    • The vehicle speed is less than 1 mph.
    • The engine coolant temperature is more than 67°C (153°F).

P0507

    • DTCs P0117, P0118, P0126, P0335, P0336, P0500, P0507, P0602, P0652, P0653, P1125 and P268A are not set.
    • The idle mode is active.
    • The vehicle speed is less than 1 mph.
    • The engine coolant temperature is more than 65°C (149°F).

Conditions for Setting

P0506

The ECM detects the actual idle speed is at least 100 RPM higher than the desired idle speed for 10 seconds.

P0507

The ECM detects the actual idle speed is 200 RPM higher than the desired idle speed for 10 seconds.

Action Taken When the DTC Sets

DTCs P0506 and P0507 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0506 and P0507 are Type B DTCs.

Diagnostic Aids

Inspect for any of the following conditions:

    • A crankcase overfill can cause oil to be forced through the positive crankcase ventilation (PCV) system.
    • An outside source that has allowed oil or fuel to enter the air induction system
    • An aftermarket performance kit using an external fuel source

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Component Views
    •  Engine Control Module Connector End Views

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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification

    Important: If you cannot duplicate the condition, 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.

  1. Engine running, compare the scan tool Desired Idle Speed parameter to the Engine Speed parameter. Both engine speed parameters should be within 50 RPM of each other.
  2. Elevate the engine speed in 25 RPM increments to 1300 RPM using a scan tool. With each commanded increment, the actual Engine Speed parameter should stay within 25 RPM of the commanded speed.

Circuit/System Testing

Important: You must perform Circuit/System Verification before proceeding with Circuit/System Testing.

  1. If there are any other DTCs set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further information.
  2. Attempt to start the engine.
    3. ⇒If the engine does not start refer to Engine Cranks But Does Not Run .
  3. Inspect for mechanical conditions that can limit engine speed.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.