A 2001 Jetta cranks but dies after two seconds. While immobilizer issues are suspected, VCDS fails to connect to any module, even with a replacement ECU. However, the original ECU connects and reads fault codes on a bench setup. This article explores potential causes, troubleshooting steps, and how to use VCDS to check oxygen sensor data in a 2001 Jetta.
Understanding the Problem: No Communication with VCDS
The inability of VCDS (Vag-Com Diagnostic System) to communicate with the car’s modules points to a fundamental communication breakdown. While a faulty ECU was initially suspected, its proper function on a bench setup eliminates that possibility. This suggests a problem lies within the car’s wiring or a critical component affecting communication. The aftermarket radio, known to interfere with the K-band communication used by some VW models, has already been removed, ruling out that common culprit.
Potential Causes and Troubleshooting Steps
Several potential issues can prevent VCDS communication:
- Faulty K-Line: The K-line is the primary communication line between VCDS and the car’s modules. Damage or a short in this wire can prevent communication. Inspecting the K-line for continuity and damage is crucial.
- Bad Ground Connection: A poor ground connection can disrupt communication. Check and clean the ground connections to the ECU and other relevant modules.
- Power Supply Issues: Insufficient power to the ECU or other modules can prevent communication. Verify the voltage at the ECU’s power supply pins and check related fuses and relays. The fault code “18010 – Power Supply Terminal 30 P1602 – 35-10 – Voltage too Low – Intermittent” supports this possibility. Further investigation into the ECM power relay control circuit fault (“17071 – ECM Power Relay Control Circuit P0687 – 35-00 – Short to Plus”) is also warranted.
- Data Bus Problems: Fault codes “18057 – Powertrain Data Bus P1649 – 35-00 – Missing Message from ABS Controller” and “18058 – Powertrain Data Bus P1650 – 35-00 – Missing Message from Instrument Cluster” indicate a problem with communication between modules on the data bus. This could be due to a faulty data bus wire, a faulty module, or a problem with the gateway module.
Focusing on Oxygen Sensor Data with VCDS
Once communication is established, VCDS can be used to analyze oxygen sensor data. Accessing Measuring Blocks in VCDS allows you to monitor real-time sensor values. For the 2001 Jetta, relevant measuring blocks for oxygen sensors likely include:
- Oxygen Sensor Voltage (Block 032): This displays the voltage output of the oxygen sensor, indicating the richness or leanness of the exhaust gases. A fluctuating voltage between 0.1V and 0.9V indicates a properly functioning sensor.
- Oxygen Sensor Heater Current (Block 033): This shows the current draw of the oxygen sensor heater. A low or zero current reading may indicate a faulty heater circuit, correlating with the fault codes “17524” and “17526” related to oxygen sensor heating.
While the numerous oxygen sensor-related fault codes (“17522”, “17511”, “16514”) found during the bench test point towards potential issues with the oxygen sensors themselves, it’s essential to address the underlying communication problem first. Resolving the communication issue will enable in-car diagnostics and accurate analysis of live oxygen sensor data through VCDS, leading to a more effective diagnosis and repair of the Jetta’s starting problem.
Conclusion
Troubleshooting a no-start condition in a 2001 Jetta requires a systematic approach. Begin by addressing the lack of communication with VCDS by inspecting the K-line, ground connections, power supply, and data bus. Once communication is restored, utilize VCDS’s Measuring Blocks feature to examine oxygen sensor data and other relevant parameters to pinpoint the root cause of the starting issue. Remember to consult the vehicle’s wiring diagram and repair manual for specific locations and procedures.
