Vehicle Information: Mileage 5497K, first maintenance completed on schedule.
Fault Phenomenon: Multiple warning lights on the dashboard illuminate, reporting DTCs as shown in Table 1. The dealership cleared the DTCs and conducted related tests, but the fault did not reappear during the test drive. After several days of use by the owner, the fault reoccurred. The dealership conducted another inspection but found no obvious abnormalities. This issue has been addressed multiple times (including replacing the dashboard and PCM), but the fault could not be completely resolved, and it is about to trigger the warranty clause: “Warranty valid for 2 years/50,000 kilometers, if the same quality issue is repaired 5 times or more, a paid vehicle replacement will be provided.”
Fault Analysis:
1. Multiple intermittent occurrences of F-CAN related DTCs. Follow the troubleshooting process for each DTC. As shown in Figure 1, when DTC U0122 and U0131 appear simultaneously with DTC 00029, first eliminate DTC 00029, while DTC U0155 is also related to 00029.
2. As shown in Figure 2, follow the DTC 00029 process to troubleshoot. During the inspection, the fault could not be reproduced, indicating it is an intermittent fault, with no freeze frame data or on-board snapshot data (only U0155 has freeze frame data, as shown in Figure 3), making it impossible to reproduce the fault. Theoretically, PCM replacement is unnecessary. This inspection process is complete.
3. As shown in Figure 4, follow the DTC U0155 process to troubleshoot. Check the F-CAN terminals between dashboard connector A and PCM connector A for any open circuits.
4. Disconnect the two unit connectors and check the F-CAN H terminal for continuity, as shown in Figure 5. Check the F-CAN_L terminal for continuity, which shows no continuity, with a resistance of approximately 1.068KΩ, as shown in Figure 6. The fault point is an open circuit in the wiring harness.
Troubleshooting: Replace the wiring harness between dashboard connector A and PCM connector A.
Experience Summary:
1. The dealership did not accurately determine the open circuit in the F-CAN_L terminal wiring harness during multiple inspections.
2. F-CAN faults exhibit diversity. According to the F-CAN circuit troubleshooting process shown in Figure 7, the F-CAN network has specified termination resistance (the resistance between PCM connector A, A3, and A4 is 50-55Ω). Abnormal line resistance can lead to intermittent F-CAN faults.
