Owner's Problem Description
The owner reports that their 2000 Infiniti i30t starts and runs normally, but when they attempt to turn off the vehicle, everything inside shuts down while the engine continues to run. Previous repairs included checking the ignition switch and fixing a broken ignition relay, but the problem persists. The vehicle is currently at a mechanic's shop, where they have to disconnect the computer under the dash to stop the engine. The owner is seeking further assistance as the issue has remained unresolved for three weeks.
Professional Technical Analysis
The vehicle in question is a 2000 Infiniti i30t equipped with a 3.0L V6 engine and an automatic transmission, with an estimated mileage of approximately 150,000 miles. The primary symptom reported is that the engine continues to run even after the ignition is turned off, which indicates a potential issue with the ignition system or related electrical components. Notably, the vehicle exhibits a complete power loss to interior accessories when the engine remains running, suggesting that the power supply to the engine management system might not be interrupted when the ignition is switched off. This issue could be attributed to a malfunctioning ignition switch, a stuck relay, or a fault in the engine control module (ECM) that fails to receive the turn-off signal. It's also essential to investigate the ECCS relay, which is integral to engine operations; if this relay is stuck in the closed position, it would prevent the engine from shutting down. Additionally, this vehicle's age and mileage may have led to wear in electrical connections or components, contributing to the failure. A thorough inspection of the ignition switch, relay function, and the overall electrical system is crucial to pinpoint the root cause of this issue. Furthermore, any stored fault codes from the ECM should be analyzed using a professional OBD-II scanner, such as the GeekOBD APP, to gather further diagnostic insights.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Switch Malfunction: A faulty ignition switch may fail to send the 'off' signal to the engine control module (ECM), allowing the engine to continue running. This can occur when the switch contacts are worn or damaged, leading to intermittent or permanent electrical connections. Testing the ignition switch for continuity when in the off position is crucial. The expected resistance should be close to infinite, and if any voltage is present at the output, the switch is likely defective. This is a common failure mode, especially in older vehicles with high mileage. - Engine continues to run while all interior lights and accessories shut off; continuity test shows voltage present at ignition switch output when turned off.
- ECCS Relay Stuck Closed: If the ECCS relay is malfunctioning and remains in the closed position, it would continue to supply power to the engine even after the ignition is turned off. This relay is critical for shutting down engine functions, and a failure here can cause continuous operation. Testing the relay with a multimeter for proper operation and replacing it if it fails to open under off conditions is necessary. Typical failure patterns include burned contacts or internal short circuits after prolonged usage. - Disconnection of the ECCS relay stops engine operation; relay does not click open when ignition is turned off.
- Engine Control Module (ECM) Fault: The ECM may have internal faults preventing it from recognizing the ignition off command. This could be due to software issues or hardware failures within the module. Diagnostic trouble codes (DTCs) should be retrieved and analyzed to check for any abnormalities. If the ECM is found to be malfunctioning, reprogramming or replacement may be necessary. Common symptoms of ECM failure include erratic engine performance and failure to shut down. - Stored DTCs related to ignition and relay operations; erratic engine behavior noted during testing.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - OBD-II Diagnostics: Start with a comprehensive scan using a professional OBD-II scanner or the GeekOBD APP to retrieve stored diagnostic trouble codes (DTCs). Pay close attention to any codes related to the ignition system, ECM, or relay operations. This step is crucial for identifying potential faults that may not be immediately apparent. Additionally, review the freeze frame data for context surrounding the fault occurrence.
- STEP 2 - Ignition Switch Testing: Conduct a continuity test on the ignition switch to ensure it is functioning correctly. Disconnect the battery first, then access the ignition switch connectors. Use a multimeter to check for continuity across the switch terminals while rotating the key through all positions. The expected result should show continuity in 'on' and 'start' positions, and no continuity in the 'off' position. Replace the ignition switch if any anomalies are found.
- STEP 3 - ECCS Relay Functionality Check: Inspect the ECCS relay for proper operation. With the vehicle in the 'off' position, measure the voltage at the relay terminals. It should read approximately 0V. If voltage is present, the relay is likely stuck closed. Further testing may require removing the relay and checking for continuity when the ignition is off. If it fails this test, replace it. Also verify the relay socket for corrosion or damage.
- STEP 4 - ECM Inspection: If previous tests do not reveal the issue, inspect the ECM for any visible signs of damage or corrosion. Additionally, check connections and wiring for any signs of wear or faults. If no physical damage is found, consider reprogramming the ECM or replacing it if it displays erratic behavior during diagnostic tests. Using the GeekOBD APP can help monitor ECM communications during testing.
