U0101 on 2007-2014 Chevrolet Silverado 1500: Lost Communication with TCM Fixes

What's Unique About the 2007-2014 Chevrolet SILVERADO 1500

The GMT900 (2007-2013) and K2XX (2014) Silverado platforms are known for having specific electrical grounding points that can become problematic over time, leading to a host of communication errors, including U0101. Manufacturer Technical Service Bulletins (TSBs) specifically mention checking the G218 body control module ground as a fix for a long list of communication codes. On 2014 and newer models, a common factory error was trapping sound-deadening insulation material under the G218 ground lug, preventing a solid connection from day one. This suggests that what appears to be a major module failure is often just a simple, but hard-to-find, bad ground.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This range covers the second generation (GMT900, 2007-2013) and the first year of the third generation (K2XX, 2014). The infamous G218 ground issue is well-documented on the 2014+ K2XX models. Similar ground-related issues are common on the GMT900s, though the exact locations may vary slightly. Most gasoline models in this range use a 6L80 transmission with an internal TCM, called a TEHCM (Transmission Electro-Hydraulic Control Module), which is located inside the transmission oil pan. Some HD models may have an external TCM mounted on the radiator shroud.

Symptoms You May Notice

• Check Engine Light is on
• Transmission may not shift or gets stuck in one gear (limp mode).
• Harsh or erratic shifting.
• Gear position indicator on the dash may be blank or incorrect.
• "Service StabiliTrak" message may appear.
• Instrument panel, radio, or HVAC controls may go blank or reset intermittently. [1, Bulletin #PIT5405B]
• Intermittent door lock cycling or chimes. [Bulletin #08-07-30-021H]
• "Service Power Steering" message may appear.

Most Likely Causes

1. Poor Body Ground Connection (G218) 🔴 High Probability Multiple TSBs and countless owner complaints point to this specific ground as a common failure point. On some 2014+ models, sound-deadening material was trapped under the ground lug from the factory, preventing a solid connection. This creates high resistance and causes intermittent communication loss for the BCM and other modules on the network.
   How to confirm: Locate the G218 ground stud under the driver's side of the dashboard, typically behind the A-pillar trim and speaker. Disassemble the connection (usually a 10mm nut), clean any paint or corrosion from the terminal and the body, and cut away any trapped insulation material. Reassemble securely.
   Typical fix: Cleaning the contact surfaces and ensuring the ground wire has a clean metal-to-metal connection. This is often a no-cost repair requiring basic hand tools.
   Est. part cost: $0
2. Damaged Wiring or Connectors 🟡 Medium Probability The wiring harness to the transmission can be exposed to heat, moisture, and vibration, leading to chafed wires, corrosion, or pushed-out pins in the main connector. This is especially common after a transmission has been replaced or serviced. Specific chafe points have been noted where the harness can rub against the ECM/TCM bracket or the shock tower. On some HD models, the TCM harness was routed too close to the serpentine belt from the factory.
   How to confirm: Visually inspect the entire wiring harness running to the transmission for any signs of rubbing, melting, or physical damage. Disconnect the main TCM connector and check for corrosion, moisture, or bent/backed-out pins. Pay close attention to the harness routing near brackets and moving parts.
   Typical fix: Repairing the damaged section of wire with a solder and heat-shrink, or cleaning/replacing the connector pigtail. In some cases, adding protective conduit and re-routing the harness is necessary.
   Est. part cost: $15-$75
3. Low Battery Voltage or Poor Battery Cables ⚪ Low Probability All control modules require a stable voltage to operate. Aging batteries or corroded battery terminals are common on older trucks and can cause unpredictable communication dropouts, especially during high electrical load events like turning the steering wheel at low speeds.
   How to confirm: Test the battery voltage with a multimeter. It should be above 12.4V with the engine off and between 13.7V and 14.7V with the engine running. TSB PIT5405C recommends checking that battery cable clamps are torqued to 7 Nm (62 lb-in) and the negative cable-to-engine block connection is torqued to 45 Nm (33 ft-lb).
   Typical fix: Cleaning battery terminals or replacing a weak battery or faulty cables.
   Est. part cost: $20-$250
4. Faulty Transmission Control Module (TCM/TEHCM) ⚪ Low Probability While the module itself can fail, it is far less common than wiring or ground issues. The TCM on these trucks is often located inside the transmission as part of the valve body (a TEHCM - Transmission Electro-Hydraulic Control Module), making it subject to heat and vibration. Internal failure from cracked pressure switch membranes or fluid intrusion is a known failure mode for the 6L80 TEHCM. However, this should only be suspected after all other causes are ruled out.
   How to confirm: This is typically the last resort after all wiring, grounds, and power sources have been confirmed to be good. Requires an advanced scan tool to attempt direct communication and confirm the module is unresponsive. Verifying battery voltage and good ground directly at the TCM connector is the final step before condemning the module.
   Typical fix: Replacing the TCM/TEHCM. This requires programming the new module to the vehicle's VIN with specialized tools.
   Est. part cost: $400-$900

Rare But Worth Checking

• Blown Fuse: A blown fuse for the TCM will cut its power and cause a U0101 code. Always check the fuse box for any fuses labeled TCM, ECM, or TRANS before beginning complex wiring diagnostics. A blown fuse can also indicate a short circuit in the wiring that needs to be found.
• Faulty Body Control Module (BCM): Since the BCM is a central hub for communication, an internal failure can sometimes disrupt the entire network, leading to communication codes for other modules. The TSBs pointing to the BCM ground (G218) highlight its importance in the network. [1, 14, Bulletin #PIT5405C]
• Aftermarket Device Interference: Poorly installed aftermarket electronics, such as remote starters, alarms, or audio equipment, can tap into CAN bus wires improperly, causing interference or network instability that leads to communication codes like U0101.

Diagnosis Steps

1. Check Battery Health: Ensure the battery has a full charge (at least 12.4V) and that the terminals are clean and tight. Verify charging voltage is 13.7-14.7V with the engine running.
2. Scan for All Codes: Use a scan tool capable of reading codes from all modules (ECM, BCM, ABS, etc.). Note all communication 'U' codes present. Multiple 'U' codes point towards a network-wide problem.
3. Inspect Fuses: Check all fuses related to the TCM, transmission, and other control modules in both the under-hood and interior fuse panels.
4. Inspect and Clean G218 Ground: Locate the G218 ground stud under the driver's side dash near the A-pillar speaker. Disconnect the battery, then remove the nut. Clean the wire terminal, the stud, and the body surface to ensure a bright metal-to-metal contact. Cut away any sound-deadening material that may be interfering with the connection. Reassemble securely.
5. Inspect TCM Connector: Locate the main electrical connector for the transmission. Disconnect it and inspect for any signs of corrosion, moisture, or pins that have backed out of the connector. Fluid contamination in the connector is a known issue.
6. Inspect Wiring Harness: Visually trace the wiring harness from the TCM to the engine bay, looking for any areas where it might be rubbing against the frame, exhaust, engine brackets, or shock towers.
7. Test CAN Bus Resistance: With the battery disconnected, use a multimeter to measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms suggests a break in the circuit or a missing terminating resistor. A reading near 0 ohms indicates a short between the two wires.

Parts You'll Likely Need

• Transmission Control Module (TEHCM) — This part is only needed if all wiring, power, and ground checks have passed, confirming the module itself has failed. On many GM 6-speed transmissions, this module is integrated with the valve body inside the transmission pan.
  Trusted brands: ACDelco, Dorman
  OEM price range: $500-$700
  Aftermarket price range: $350-$550

Related Codes That Often Appear With This One

• U0100 — Lost Communication with ECM/PCM. Like U0101, this indicates a network problem. Seeing them together strongly suggests a widespread issue like a bad ground or CAN bus wiring fault, rather than a single failed module. [Bulletin #08-07-30-021H]
• U0073 — Control Module Communication Bus 'A' Off. This is a general network code indicating the entire CAN bus has shut down, often due to a short in the wiring or a bad ground. It is frequently cited alongside U0101 in TSBs. [1, Bulletin #PIT5405C]
• P0700 — Transmission Control System Malfunction. This is a generic code sent by the ECM when it detects any fault has been stored in the TCM. It's an informational code that tells the technician to scan the TCM for more specific codes, but if the TCM isn't communicating (U0101), P0700 will be present.

Technical Service Bulletins (TSBs) & Recalls

• PIT5405C: Addresses a wide range of electrical issues including multiple 'U' codes, stalls, and blank instrument panels, pointing to the G218 ground as a primary cause. It specifically mentions cutting away sound-deadening material.
• 08-07-30-021H: Lists several communication DTCs, including U0101, as being related to intermittent network issues that can also cause door lock cycling and warning lamps.
• PIT5405B: An earlier version of PIT5405C, also pointing to the G218 ground as the culprit for a list of communication codes and electrical symptoms.
• 21-NA-149: While for a later model year, this bulletin details common engine wiring harness chafe points against the ECM/TCM bracket and shock tower, which are relevant inspection areas for the 2007-2014 models as well.

Platform-Specific Known Issues

• Factory Defect: Sound Deadening Under G218 Ground: On 2014 models in particular, a common manufacturing flaw was the placement of the dash sound-deadening mat over the G218 ground stud. This prevented the ground eyelet from making solid contact with the metal body, causing high resistance and a host of intermittent communication codes, including U0101. The fix is to remove the ground, cut away the mat, and re-secure the connection.
• Post-Repair Communication Loss: Many owners report the sudden appearance of U0101 immediately after a transmission replacement or other major engine work. This is almost always due to either the main transmission electrical connector not being fully seated, pins being damaged during removal/installation, or the harness itself getting pinched or chafed against the bellhousing or frame during the procedure.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: Approximately 60 Ω (Ohms) when measured between Pin 6 (CAN High) and Pin 14 (CAN Low) at the DLC with the battery disconnected.. Failure: A reading of 120 Ω indicates an open circuit or a missing terminating resistor on one end of the bus. A reading near 0 Ω indicates the CAN High and Low wires are shorted together.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6 at DLC) should be 2.5-3.5V. CAN Low (Pin 14 at DLC) should be 1.5-2.5V.. Failure: Voltages outside these ranges indicate a potential short to power or ground on the bus.
• TCM/TEHCM Power Supply Voltage — expected: Should be equal to battery voltage (approx. 12.6V with key on, engine off) at the appropriate power supply pin on the TCM connector.. Failure: Low or no voltage indicates a problem with the fuse, relay, or wiring supplying power to the module.
• TCM/TEHCM Ground Circuit Resistance — expected: Less than 0.5 Ω between the TCM ground pin and a known good chassis ground.. Failure: High resistance indicates a poor ground connection, which is a very common cause of communication issues.

Scan Tool Commands That Help

• GDS2/Tech2: Module Communication Test / Bidirectional Data — After verifying power and ground to the TCM, a technician can use a factory scan tool to send a direct request to the TCM. If the module does not respond, it confirms it is offline and likely faulty, assuming the CAN wiring to it is intact.
• GDS2/Tech2: Transfer Case Relearn — On 4WD models, if the TCM is replaced or reprogrammed, a transfer case relearn procedure may be necessary. Failure to do this can result in the vehicle being stuck in four-wheel drive low.

Wiring & Ground Locations

• G218 — Under the driver's side of the dashboard, behind the A-pillar trim panel and speaker.. This is a primary body ground connection. Multiple TSBs cite a poor connection at this point as the cause for a wide range of communication codes, including U0101. On 2014 models, sound deadening material was often trapped under the ground lug from the factory.
• TCM Connector (External, HD Models) — Mounted on the radiator shroud in the engine bay for some Duramax/Allison models.. This is the main connection point for testing power and ground to an external TCM. Key pins to check for voltage are Pin 10 and Pin 70 (Battery Positive) and Pin 2 (Ignition Hot). Key ground pins are 9 and 69.
• TEHCM Connector (Internal, 6L80) — Inside the transmission oil pan, connected to the Transmission Electro-Hydraulic Control Module (TEHCM). The external pass-through connector is on the driver's side of the transmission case.. The external connector is a common point for fluid contamination or pin damage. The internal location means the module itself is subject to extreme heat and vibration, which can lead to failure.
• G110 — On the rear of the passenger side cylinder head on V8 gasoline engines.. This is a major engine and harness ground. While less commonly cited for U0101 than G218, a poor connection here can cause various electrical issues. Later models (2019+) have known issues with loose G110 grounds.

Real Owner Repair Stories

• YouTube channel 'Duramax No Crank, No Start' (2007 Silverado/Sierra Classic Duramax) — No crank, no start condition with U0101 and U1000 codes stored in multiple modules. The TCM was not communicating.
  ❌ Tried (didn't work) Initial assumption was a failed TCM, which is a common failure on these models.
  ✅ What actually fixed it The technician found a 40-amp blown fuse. Further diagnosis revealed the cause of the blown fuse was a shorted wire in the harness for the trailer brake control module, which had rubbed through on a bracket. Repairing the wire and replacing the fuse restored communication and fixed the truck.
• YouTube user comment on 'G218 Ground Issue Fix' video (2014-2018 Silverado/Sierra (specifics not given)) — Unspecified electrical issues consistent with the G218 ground problem.
  ❌ Tried (didn't work) Hours of online research trying to diagnose the problem.
  ✅ What actually fixed it Following the video's instructions, the owner located the G218 ground, found the sound-deadening foam trapped under the connection, cut it away, and re-secured the ground. The fix took 30 minutes and resolved all issues.

OEM Part Supersession History

• A50 TCM (e.g., 29545320) → A40 / T14A TCM (e.g., 29544139) — Part availability issues for the original A50 TCM used in 2011-2014 Allison 1000 transmissions.
  Heads up: A user reported successfully using the A40/T14A module as a plug-and-play replacement for the A50. However, it required a transfer case relearn procedure using a scanner to restore 4WD functionality. Without the relearn, the truck may shift strangely and 4WD will be inoperative.

Model Year Variations Within This Range

• 2007-2014 (6-speed Automatic 6L80/6L90): Most of these trucks are equipped with the 6L80/6L90 transmission, which features an integrated TCM and valve body assembly called a TEHCM (Transmission Electro-Hydraulic Control Module). This entire unit is located inside the transmission oil pan, making it susceptible to heat and fluid contamination.
• 2014: The 2014 model year marked the transition to the K2XX platform. These models are particularly known for the factory defect where sound-deadening material was incorrectly installed under the G218 ground lug, causing a poor connection from the start.
• 2007-2014 (HD Models w/ Allison): Heavy-duty models equipped with the Allison transmission typically use an external TCM mounted in the engine bay, often on the radiator support shroud. This makes access for testing power, ground, and communication wires at the connector much easier than on models with an internal TEHCM.