Jeep Grand Cherokee - Crank No Start/No Comms

Introduction

This tutorial provides a step-by-step guide to diagnosing and resolving a crank no start issue in a 2002 Jeep Grand Cherokee. This problem can manifest as intermittent stalling followed by continuous crank without starting. Understanding how to approach this issue can save time and frustration for DIY mechanics and car enthusiasts.

Step 1: Initial Assessment

• Check for Warning Lights: Inspect the dashboard for any warning lights that may indicate electrical issues.
• Listen for Sounds: When turning the key to the "on" position, listen for the fuel pump engaging. A lack of sound may indicate a fuel system issue.
• Verify Battery Condition: Ensure the battery is fully charged and connections are clean and tight. A weak battery can prevent starting.

Step 2: Scan for Diagnostic Trouble Codes (DTCs)

• Use an OBD-II Scanner: Connect an OBD-II scanner to the vehicle’s diagnostic port to retrieve any stored trouble codes.
• Interpret Codes: Look up any codes related to the ignition or fuel system. Common codes may point directly to the problem area.

Step 3: Inspect Fuses and Relays

• Locate the Fuse Box: Check the vehicle's manual for the location of the fuse box.
• Inspect Fuses: Look for blown fuses related to the fuel pump and ignition system.
• Test Relays: Swap or test relays for the fuel pump and ignition to ensure they are functioning correctly.

Step 4: Examine the Fuel System

• Check Fuel Pump Operation: If you didn't hear the fuel pump in Step 1, perform a fuel pressure test using a gauge.
• Inspect Fuel Filter: Ensure the fuel filter is not clogged, which could restrict fuel flow.
• Review Fuel Lines: Check for leaks or blockages in the fuel lines.

Step 5: Investigate the Ignition System

• Test Spark Plugs: Remove a spark plug and use a spark tester to check for a spark when cranking the engine.
• Inspect Ignition Coils: Ensure the ignition coils are functioning; replace any faulty coils.
• Check Wiring: Look for damaged wires or loose connections in the ignition circuit.

Step 6: Assess the Crankshaft Position Sensor

• Locate the Sensor: Find the crankshaft position sensor, typically located near the bottom of the engine.
• Test Sensor Functionality: Use a multimeter to check the sensor's resistance. Replace if it is out of specification.

Step 7: Evaluate the Engine Control Module (ECM)

• Check for Corrosion: Inspect the ECM connectors for corrosion or damage.
• Reflash or Replace: If other diagnostics point to a faulty ECM, consider reflashing it or replacing it.

Conclusion

By following these steps, you can systematically diagnose and resolve crank no start issues in a 2002 Jeep Grand Cherokee. Start with basic assessments and progressively check each system involved in the starting process. If the issue persists after these steps, consider consulting a professional mechanic for further diagnosis. Always ensure safety first when working on your vehicle.