Experiencing a no-start issue with your 2008 Toyota Corolla can be frustrating, especially when you can’t even pull diagnostic codes. If you’re facing a situation where your OBD2 scanner won’t communicate with your Corolla, and the engine cranks but doesn’t start, you’re in the right place. Let’s explore the potential causes and troubleshooting steps for a 2008 Corolla with no OBD2 communication and a no-start condition.
Diagnosing the OBD2 Communication Failure
The inability to communicate with your car’s computer via the OBD2 port is a significant issue that needs to be addressed first. When your OBD2 scanner powers up but fails to establish a connection, it indicates a problem within the communication network or power supply to the diagnostic system. Here’s a breakdown of what to check:
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Verify OBD2 Port Power: You’ve already confirmed that your OBD2 port has power since your scan tool powers on. This is a good initial step.
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Inspect Relevant Fuses: While you checked the 7.5 amp fuse, it’s crucial to verify all fuses related to the Engine Control Module (ECM), Powertrain Control Module (PCM), and the OBD2 system itself. Refer to your 2008 Toyota Corolla’s fuse box diagram (usually found in your owner’s manual or on the fuse box cover). Look for fuses labeled “OBD,” “ECU-B,” “EFI,” or similar terms. A blown fuse in a different location could still be the culprit.
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Scan Tool Compatibility: Although less likely with a professional scan tool, ensure your scan tool is compatible with OBD2 protocols and specifically with 2008 Toyota Corolla models. Most generic OBD2 scanners should work, but it’s worth double-checking.
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OBD2 Port Wiring and Connections: Inspect the OBD2 port itself for any signs of damage or corrosion. Check the wiring harness leading to the OBD2 port for any cuts, breaks, or loose connections. Sometimes, physical damage to the port or its wiring can disrupt communication.
Investigating the No Start Condition
Separately from the OBD2 issue, let’s address the no-start problem. You’ve made some good initial checks: airflow is good, and you’re planning to test for spark. Let’s delve deeper into potential no-start causes:
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Fuel System Analysis: You’ve noted no fuel pressure at the fuel rail and constant power to the fuel tank. This constant power to the fuel pump, even with the car off, is unusual and a key point of investigation. It suggests a potential issue with the fuel pump relay or the fuel pump control circuit. A stuck or faulty fuel pump relay could be continuously powering the pump, but if there’s no fuel pressure, the pump itself might be failing, or there’s a blockage in the fuel line.
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Ignition System Check: Testing for spark at the coil packs is the next logical step. No spark would prevent the engine from starting. If there’s no spark, consider issues with the crankshaft position sensor, camshaft position sensor, or the ignition system itself.
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Check Engine Light (CEL) Absence: The fact that the “Check Engine” light doesn’t illuminate when you turn the key to the “RUN” position is concerning and potentially very significant. Typically, the CEL should briefly illuminate as a bulb check when you turn the ignition on. The absence of the CEL, combined with no OBD2 communication, strongly suggests a problem with the ECM/PCM’s power supply or the ECM/PCM itself. The ‘Maintenance Required’ light illuminating is a separate system and doesn’t confirm the ECM/PCM is fully functional.
Are the OBD2 and No Start Problems Related?
Given the symptoms – no OBD2 communication and no start, especially with the missing CEL – it’s highly probable that these issues are interconnected. The ECM/PCM controls both engine management functions (fuel, ignition, etc.) and OBD2 communication. If the ECM/PCM is not functioning correctly due to a power supply issue, internal failure, or a grounding problem, it could explain both the no-start and the lack of OBD2 communication.
Advanced Troubleshooting and Next Steps
To move forward, focus on diagnosing the ECM/PCM and its related systems:
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ECM/PCM Power and Ground: Locate the ECM/PCM (usually under the dashboard or in the engine bay). Check for power and ground at the ECM/PCM connectors using a multimeter. Refer to wiring diagrams for your 2008 Toyota Corolla to identify the correct pins for power and ground. Ensure the ECM/PCM is receiving both power and ground.
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ECM/PCM Relays: Identify and test the relays associated with the ECM/PCM and the fuel pump. A faulty relay can prevent power from reaching these components. You can often swap identical relays in the fuse box to test if a relay is the problem.
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Inspect ECM/PCM Connectors and Wiring: Carefully inspect the ECM/PCM connectors for corrosion, bent pins, or damage. Check the wiring harness leading to the ECM/PCM for any signs of damage.
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Professional Diagnostic Scan: If you’ve checked fuses, relays, and basic wiring and are still facing the same issues, it’s advisable to seek professional help from a qualified mechanic or diagnostic specialist. They have advanced scan tools and diagnostic equipment to further pinpoint the problem, potentially including testing the CAN bus network and performing deeper ECM/PCM diagnostics.
In conclusion, for your 2008 Toyota Corolla, the lack of OBD2 communication, coupled with the no-start condition and missing CEL, points towards a potential issue with the ECM/PCM power supply or the ECM/PCM itself. Systematically checking fuses, relays, power, and ground to the ECM/PCM is crucial. If DIY troubleshooting doesn’t resolve the issue, professional diagnostic assistance is recommended to accurately identify and repair the root cause.
