A Toyota Highlander Hybrid presented with a no-start condition, displaying diagnostic trouble codes (DTCs) P3190 (ICE won’t stay running), P3191 (ICE won’t start), and a history of P3193 (no start & fuel empty). This article outlines the diagnostic process undertaken to identify the root cause of this issue.
Initial Diagnosis and Customer Information
The vehicle stalled a short distance from the owner’s driveway after seemingly starting normally. The driver reported a successful “restart” before the vehicle ultimately died. The fuel gauge indicated half a tank, confirmed by the owner who stated no recent refueling. Initial code retrieval revealed the aforementioned DTCs. Freeze Frame Data (FFD) for P3191 showed 500 RPM (lower than normal), approximately 3g/sec Mass Air Flow (MAF) sensor reading (likely normal for the low RPM), and 2.59V Air Fuel Sensor (AFS) signal indicating a rich condition.
Diagnostic Steps and Findings
Codes were cleared, and a restart attempt was made. The engine cranked and occasionally “kicked,” accompanied by a drop in RPM on the graphing tool, possibly indicating a timing issue. However, subsequent oscilloscope testing of the cam timing revealed no abnormalities.
Further investigation included checking the Ignition Trigger (IGT) signal on cylinder #2 and the Ignition Feedback (IGF) signal. While the patterns appeared generally normal, some spikes were observed on the falling edge of the IGT signal every 120 degrees. Coil ground was checked and found to be within specifications.
Spark plug inspection revealed a dark color and strong fuel smell. The vehicle had six relatively new Denso coils installed approximately 50,000 miles prior. A compression test on cylinder #6 yielded 150 PSI. Fuel pressure measured a normal 45 PSI, and the fuel itself smelled normal, with no indication of diesel contamination.
Throttle valve operation was assessed using an oscilloscope and Techstream software. Initial testing showed intermittent unresponsiveness of the Throttle Position Sensor (TPS) during changes in throttle body motor duty cycle. However, direct manipulation of the throttle valve via Techstream’s active test resulted in consistent movement, suggesting proper functionality.
Live data recording during cranking revealed full rich readings from both air-fuel sensors (B1 and B2), accompanied by negative fuel trims. Injector signal duration on injector 2 measured around 4.6ms, decreasing during cranking.
Conclusion and Remaining Questions
Despite verifying compression, timing, spark, and the presence of (excess) fuel, the root cause of the P3190 in this Toyota Highlander Hybrid remained elusive. The diagnostic process eliminated several potential culprits, leading to further questions. Could the intermittent TPS behavior observed initially still be a factor? Are the spikes on the IGT signal significant? A known-good IGT #1 and Crankshaft Position (CKP) sensor waveform for comparison would be beneficial in further analysis. This case highlights the complexities of hybrid vehicle diagnostics and the importance of thorough and systematic troubleshooting.
