Engine Cranks Slowly

Engine Cranks Slowly

Diagnostic Instructions

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

Reference Information
Schematic Reference

Starting and Charging Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Starting System Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Verification

1. Ignition OFF, measure and record the battery voltage at the C1 terminals. The voltage should be between 12.0-15.0 V.

• If not within the specified range, refer to Battery Inspection/Test (Battery Inspection/Test).

2. Remove the drive belts. Refer to one of the following:

* Drive Belt Replacement (Service and Repair) for the 4.3L (LU3) engine
* Drive Belt Replacement (Service and Repair) for the 6.6L Diesel (LML) engine
* Drive Belt Replacement - Accessory (Service and Repair) for all other engines (without LU3 or LML)
* Air Conditioning Compressor Belt Replacement (V8) (Service and Repair) for all other engines (without LU3 or LML)

3. Ignition Start, verify the engine does not crank normal.

• If the engine cranks normal, inspect the engine and belt drive system for mechanical binding, seized engine, or seized generator.

4. Verify that a test lamp illuminates between the M64 starter motor B+ terminal A X2 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Test for less than 0.5 V between the positive battery cable and terminal A X2 at the M64 starter motor as ignition is switched to start position.

• If greater than the specified value, replace the positive battery cable.

6. Test for less than 0.5 V between the negative battery cable and the M64 starter motor case as ignition is switched to start position.

• If greater than the specified value, replace the negative battery cable.

7. If all circuits test normal, replace the M64 starter motor.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Battery Positive Cable Replacement (Diesel) (Battery Positive Cable Replacement)Battery Positive Cable Replacement (Gas) (Battery Positive Cable Replacement)Battery Positive Cable Replacement (TP2) (Battery Positive Cable Replacement (TP2))
* Battery Negative Cable Replacement (Diesel) (Service and Repair)Battery Negative Cable Replacement (V8) (Service and Repair)Battery Negative Cable Replacement (V6) (Service and Repair)
* Starter Replacement (V8) (Service and Repair)Starter Replacement (V6) (Service and Repair)Starter Replacement (Diesel) (Service and Repair)