Important: Cranking speed is critical for a diesel engine to start, whether the engine is hot or cold. The only approved method to test cranking speed is to use a Tech 2 Diagnostic Scan Tool.

1. Ensure that the vehicle's batteries are in good condition, and fully charged. Refer to Battery Inspection/Test in Engine Electrical.
2. Remove the ECM 1 fuse in the underhood fuse block.
3. Connect the Scan Tool .
4. Crank the engine for 2 to 4 seconds. This will allow the starter to reach it's maximum performance.
5. Observe the engine RPM reading on the Scan Tool . Refer to Engine Mechanical Specifications . The actual cranking speed needed for starting will vary depending on the condition of the engine mechanical components, compression, and the condition of the fuel system components, fuel injection pump operating pressure, and fuel injection nozzles cracking pressure and spray pattern.
6. If the engine fails to meet the minimum specified cranking speed, repair or replace damaged or malfunctioning components and retest.
7. Disconnect the Scan Tool .
8. Install the ECM 1 fuse.