Experiencing a no-start issue with your 1999 Buick LeSabre and finding your OBD2 scanner unable to communicate can be a perplexing situation. This combination of problems often points towards deeper electrical or system failures beyond a simple fix. Let’s delve into the potential causes and diagnostic steps for a 1999 Buick LeSabre exhibiting “OBD2 no communication no start”.
Understanding why your OBD2 scanner isn’t connecting is crucial. The On-Board Diagnostics II (OBD2) system is designed to communicate vital vehicle information, and its failure to connect often signals a significant problem within the car’s computer network or power supply to the diagnostic port itself. When coupled with a no-start condition, the issue is likely preventing essential engine management functions from operating.
Several factors could contribute to this frustrating scenario:
Potential Causes for OBD2 No Communication and No Start:
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Power and Ground Issues: The OBD2 port and the Powertrain Control Module (PCM) both require stable power and ground connections. A blown fuse, a faulty relay, or wiring issues can interrupt power supply, leading to both no communication and no start conditions. Specifically, check fuses related to the PCM, ECM, and diagnostic link connector (DLC). A poor ground connection can also similarly disrupt system operation.
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Faulty PCM or BCM: The PCM (Powertrain Control Module) is the primary computer controlling engine functions, and the BCM (Body Control Module) manages other vehicle systems. If either of these modules has failed, it can result in a no-start condition and prevent OBD2 communication. While less common, module failure is a definite possibility, especially in older vehicles.
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Security System/Passkey Issues (VATS): The 1999 Buick LeSabre likely utilizes GM’s Vehicle Anti-Theft System (VATS), often involving a resistor pellet in the ignition key. If the VATS system malfunctions or fails to recognize the key, it can disable the fuel and ignition systems, causing a no-start. Furthermore, VATS issues can sometimes interfere with OBD2 communication. Problems with the key resistor, wiring to the ignition switch, or the VATS module itself can be culprits.
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Wiring and CAN Bus Problems: The OBD2 system and various vehicle modules communicate via a network, often a Controller Area Network (CAN bus). Damage to wiring, corroded connectors, or shorts in the CAN bus system can disrupt communication between modules, including the PCM and the OBD2 port. This can manifest as both no communication and no start.
Diagnostic Steps to Consider:
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Check Fuses and Relays: Begin by inspecting all relevant fuses and relays in both the under-hood and under-dash fuse boxes. Specifically look for fuses related to the PCM/ECM, ignition, and diagnostic connector. Replace any blown fuses and test relays if possible.
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Inspect OBD2 Port Power and Ground: Use a multimeter to check for power and ground at the OBD2 port (pin 16 should have 12V+, pins 4 and 5 are ground). Lack of power or ground here will directly prevent scanner communication.
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Evaluate Battery Condition and Connections: A weak battery or poor battery terminal connections can cause a multitude of electrical issues. Ensure the battery is properly charged and that battery terminals and cables are clean and tight.
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Scan with a High-End Scanner: While your current scanner may not be communicating, try using a more advanced scan tool, preferably one with CAN bus diagnostic capabilities, or a GM Tech 2 scanner if accessible. These tools may be able to establish communication where generic scanners fail and provide more in-depth diagnostic information.
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Check for VATS Issues: If you suspect a VATS problem, try a spare key if available. Listen for any clicking from the fuel pump relay when turning the key to the ‘ON’ position – lack of fuel pump activation can be a VATS symptom. Professional VATS diagnostics may be necessary.
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Inspect Wiring and Connectors: Visually inspect wiring harnesses, particularly those around the PCM, BCM, ignition switch, and OBD2 port for any signs of damage, rodent intrusion, or corrosion. Check connectors for secure seating and clean contacts.
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PCM/BCM Testing: Diagnosing a faulty PCM or BCM often requires specialized equipment and knowledge. If basic checks don’t reveal the issue, module testing or replacement (followed by programming) may be necessary, typically best performed by a qualified technician.
Conclusion:
A 1999 Buick LeSabre with “OBD2 no communication no start” presents a complex diagnostic challenge. Systematic troubleshooting, starting with basic checks of power, grounds, and fuses, and progressing to more advanced diagnostics of modules and wiring, is essential. Due to the potential involvement of security systems and sophisticated electronic components, seeking assistance from a professional automotive technician experienced with GM vehicles may be the most efficient path to resolving this issue. They will have the tools and expertise to accurately pinpoint the root cause and implement the necessary repairs, potentially including PCM or BCM reprogramming if module replacement is required.
