This article addresses a no-crank issue in a 2008 Chevy Cobalt, focusing on potential problems related to the OBDII system and ignition. It draws upon a forum discussion where users troubleshoot similar problems, providing a more comprehensive and clarified guide for diagnosing and fixing the issue.
Understanding the Problem: No Crank in a 2008 Chevy Cobalt
A no-crank situation means the engine doesn’t turn over when the key is turned to the “start” position. While there can be various causes, this article delves into a specific scenario discussed in an online forum concerning a 2008 Chevy Cobalt. The original poster ruled out a faulty fuse and focused on potential issues with the Body Control Module (BCM) and ignition switch, referencing a previous thread about an engine swap in a similar vehicle.
Analyzing BCM and Ignition Switch Signals
The original forum discussion highlights the importance of checking voltage signals at specific pins on the BCM connector (C2). User “1966tbird” provides detailed instructions for voltage testing using a Digital Volt Meter (DVM):
- Pin 62 (BCM C2): This pin supplies a +5V reference voltage to the ignition switch. It should consistently read +5V with a good battery and fuses.
- Pin 56 (BCM C2): This pin receives the signal back from the ignition switch. The voltage on this pin should vary depending on the key position: 0V when off, ~+5V in the “run” position, and ~1.5-2.5V in the “start” position.
The original poster’s readings deviated from the expected values, particularly on pin 62, raising questions about the ignition switch or wiring.
Example of voltage testing at the BCM
Performing an Ignition Switch Continuity Test
Beyond voltage checks, “1966tbird” also recommends a continuity test of the ignition switch itself with the battery disconnected and BCM C2 connector unplugged. This test involves measuring resistance between specific pins on the C2 connector:
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Pin 56 and Pin 61 (or Pin 62 in this specific case): With the key in the “on” position, there should be continuity (low resistance) between these pins. In the “start” position, the resistance should be a few kiloohms. With the key out, the circuit should be open (infinite resistance). The original poster confirmed this test passed, seemingly ruling out a faulty ignition switch.
Example of an ignition switch continuity test
Further Diagnostic Steps
While the original poster’s tests eliminated some common culprits, the root cause remained unclear. Potential next steps, building upon the information provided, include:
- Wiring Harness Inspection: Thoroughly inspect the wiring harness between the ignition switch and the BCM for any damage, corrosion, or loose connections. Pay close attention to the wires associated with pins 56 and 62 on the BCM C2 connector.
- BCM Ground Check: Verify that the BCM has a good ground connection. A poor ground can lead to erratic voltage readings and malfunctions.
- Advanced Diagnostics: If the above steps don’t reveal the problem, more advanced diagnostics using a professional scan tool capable of reading Chevy-specific trouble codes and data streams may be necessary. This could pinpoint issues within the PCM (Powertrain Control Module) or other related modules.
Conclusion
Troubleshooting a no-crank issue in a Chevy Cobalt requires a systematic approach. This article, based on a real-world forum discussion, highlights the importance of checking voltage and continuity at key points in the ignition system, specifically focusing on the BCM and ignition switch. While the original problem remained unresolved in the forum thread, the outlined procedures and suggested next steps provide a solid foundation for diagnosing similar no-crank problems, potentially saving time and expense. Remember to consult a qualified automotive technician for assistance if you lack experience working with automotive electrical systems.
