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2008 Chevrolet Trailblazer U0101 Code: Lost Communication with Transmission Control Module (TCM)

Model: 2008 Trailblazer Fault Code: U0101 Posted: 2018-07-19 14:26

I'm experiencing a U0101 diagnostic trouble code on my 2008 Chevrolet Trailblazer. The vehicle shows that it's in first gear when started, and the speedometer reads 155 mph at idle—this is clearly incorrect. OBD-II live data confirms abnormal VSS readings while RPMs and other cluster functions are normal. The U0101 code indicates a lost communication with the Transmission Control Module (TCM). Possible causes include: - Faulty wiring or poor electrical connections to the TCM - Voltage issues at the TCM module - Damaged LAN communication lines between the TCM and Engine Control Module (ECM) - Alternator diode failure causing voltage spikes that interfere with sensor signals I've already checked the fuses related to the TCM, but the issue persists. Any guidance on troubleshooting steps or wiring diagrams for this model would be greatly appreciated.

Related fault codes
U0101
Comments (4)
Anonymous 2018-07-20 08:09

What year and model of your Trailblazer? The U0101 code typically indicates lost communication with the Transmission Control Module (TCM). Common troubleshooting steps include checking wiring harnesses for voltage at the TCM and verifying LAN communication lines between the TCM and ECM.

Anonymous 2018-07-20 08:38

Check the fuses in the fuse box that supply power to the TCM. A blown fuse could be causing a loss of signal or power to the transmission control module, leading to U0101 code activation.

Anonymous 2018-07-20 16:44

kev2 wrote: Fri Jul 20, 2018 8:09 am What year and model? The U0101 code indicates lost communication with the TCM. Check wiring for voltage at the TCM and ensure LAN communication lines between TCM and ECM are intact. I have a 2008 Trailblazer. What's odd is that every time I start the vehicle, it shows in first gear. I used OBD-II live data and noticed my VSS reading jumps to 155 mph at idle—speedometer isn't working properly. RPMs and other cluster functions are normal.

Anonymous 2018-07-21 10:17

A likely cause for the speedometer malfunction is faulty alternator diodes, which can generate voltage spikes that interfere with sensor signals. After checking TCM power supply as suggested, I would also inspect the alternator output and grounding connections. Since this is a 2008 Trailblazer, referencing specific wiring diagrams for the TCM and VSS system is recommended.