Code
U0101
Generic
U — Network/User
Lost Communication With TCM
Views:
UK: 39
EN: 63
RU: 85
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between TCM and other modules
- Corroded or loose connector at the TCM or intermediate connector
- No power (battery/ignition feed) or poor ground to the TCM
- Failed TCM (internal electronics or firmware) or failed gateway/module
- Missing or faulty CAN bus termination resistor
- Low battery voltage or intermittent supply
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
- Transmission malfunction messages or 'Service Transmission' message in cluster
- No shifting, default/limp transmission behavior or stuck in one gear
- Unable to communicate with TCM using diagnostic scan tool
- Related systems that rely on TCM data may show faults or degraded function
- Intermittent or permanent loss of gear indicator or shift selection display
What to check
- Read and record all current and pending U-codes and freeze frame data with a scan tool
- Attempt to communicate with the TCM with a diagnostic tool at key ON and engine running
- Check battery voltage (should be ~12–14V during testing) and note any drops under cranking
- Inspect and verify fuses and relays that supply power to the TCM and gateway
- Visually inspect TCM connectors and harness for corrosion, bent pins, water damage, or loose terminals
- Perform a wiggle test on harness and connectors while watching for communication loss
Signal parameters
- CAN bus idle (recessive) voltages: CANH ≈ 2.5–2.7 V, CANL ≈ 2.5–2.3 V (node-dependent)
- CAN bus dominant bit voltages: CANH ≈ 3.5–4.0 V, CANL ≈ 1.0–1.5 V (differential ≈ 2.0 V)
- Expected termination resistance across CANH–CANL: ~60 ohms (two 120Ω terminators in parallel)
- Typical CAN bus speeds: commonly 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- TCM supply voltage (Key ON): battery voltage ~12 V; ground continuity to chassis
Diagnostic algorithm
- Verify the U0101 code and capture freeze-frame data and any related U-codes. Note if code is intermittent.
- Confirm battery state and reliable power supply. Charge or connect a stable battery if voltage is low.
- Try to communicate with the TCM using a manufacturer-level scan tool. If tool cannot see TCM, confirm which modules are present on the bus.
- Inspect fuses and relays for the TCM and replace any blown items. Re-test communication after replacement.
- Visually inspect and disconnect the TCM connector(s). Check pins for corrosion, damage, or pushed-out terminals. Re-seat securely.
- Measure power and ground at the TCM connector. Repair open feeds or poor grounds before replacing modules.
- With ignition ON, measure CANH and CANL at the TCM and at the PCM/gateway. Compare voltages and waveform integrity using an oscilloscope if available.
- Check termination resistance (with power off) between CANH and CANL. If not near expected ~60 ohms, isolate segments to locate missing/extra terminators or an open circuit.
- Isolate wiring faults by disconnecting other nodes or harness branches and re-check bus presence. Use backprobing and continuity checks to find opens or shorts.
- If short to battery or ground is suspected, use a current-limited test lamp or bench supply and isolate sections until the short is located and repaired.
- After wiring/connectors are repaired, clear codes and verify TCM communication. Perform a road test to ensure the issue does not return.
- Replace or reprogram the TCM only after confirming the network and power/ground are good. Follow OEM programming and configuration procedures if replacement is required.
Likely causes
- Damaged or disconnected CANH/CANL wiring at the harness or connector
- Power or ground circuit fault at the TCM (blown fuse, open feed, bad ground)
- Corroded/poor connector pin preventing communication
- Short to battery or ground on the CAN bus (shorted CANH or CANL)
- Faulty TCM or gateway module (replace only after wiring verified)
Fault status
Status
U0101 — Lost Communication With TCM: The Transmission Control Module is not responding on the vehicle communication bus. Possible causes include CAN wiring faults, lack of TCM power/ground, missing termination, or a failed module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Workshop Manuals
Available brands with manuals
2
AUDI 11
6-speed manual gearbox 0B1, front-wheel drive — Workshop Manual (Edition 05.2014)
Workshop ManualAudi A3 (1997) – 1.6L 4-cylinder (2‑valve) Engine Mechanical Components Service Manual (AEH, AKL, APF) – Edition 07.2002
Workshop ManualAUDI A3 (2004) Workshop Manual — 2.0L FSI Turbo (4‑cyl, 4‑valve) Engine, Mechanics — Edition 03.2017
Workshop ManualAudi A3 2004 — Electrical System (Workshop Manual, Edition 02.2018)
Workshop ManualAudi A4 / A4 Cabriolet – 4.2 l V8 (5‑valve, timing chains) – Workshop Manual (Mechanics) – Edition 04.2007
Workshop ManualAudi A4 / A4 Cabriolet — Auxiliary Heater Workshop Manual (Edition 08.2004)
Workshop ManualAudi A4 / A4 Cabriolet (1.8T 4‑cyl turbo) — Motronic Injection & Ignition System Service Manual (Edition 01.2015)
Workshop ManualAudi A8 (2003) — Electrical System Workshop Manual (Edition 08.2014)
Workshop ManualAudi Q4 e-tron (Type F4) - Self-study Programme SSP 685
Workshop ManualAudi Q8 (2018) — Electrical System Workshop Manual (Edition 05.2019)
Workshop ManualAudi Servicing Manual — 7‑Speed Dual Clutch Transmission 0CJ / 0CL / 0CK / 0DN / 0DP / 0HL (Edition 05.2018)
Workshop ManualLAND ROVER 3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualLand Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualLand Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop ManualYour experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email
Code
U0101
HYUNDAI
U — Network/User
Lost Communication with TCM | Lost Communication With TCM | Serial Communication Problem With TCM | Lost Communication With ECM/PCM ‘A’ (C-CAN) | Lost Communication with TCM (C-CAN) | Lost Communication with ECM/PCM ‘A’
Views:
UK: 25
EN: 44
RU: 60
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between TCM and other modules
- Corroded or loose connector at the TCM or intermediate connector
- No power (battery/ignition feed) or poor ground to the TCM
- Failed TCM (internal electronics or firmware) or failed gateway/module
- Missing or faulty CAN bus termination resistor
- Low battery voltage or intermittent supply
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
- Transmission malfunction messages or 'Service Transmission' message in cluster
- No shifting, default/limp transmission behavior or stuck in one gear
- Unable to communicate with TCM using diagnostic scan tool
- Related systems that rely on TCM data may show faults or degraded function
- Intermittent or permanent loss of gear indicator or shift selection display
What to check
- Read and record all current and pending U-codes and freeze frame data with a scan tool
- Attempt to communicate with the TCM with a diagnostic tool at key ON and engine running
- Check battery voltage (should be ~12–14V during testing) and note any drops under cranking
- Inspect and verify fuses and relays that supply power to the TCM and gateway
- Visually inspect TCM connectors and harness for corrosion, bent pins, water damage, or loose terminals
- Perform a wiggle test on harness and connectors while watching for communication loss
Signal parameters
- CAN bus idle (recessive) voltages: CANH ≈ 2.5–2.7 V, CANL ≈ 2.5–2.3 V (node-dependent)
- CAN bus dominant bit voltages: CANH ≈ 3.5–4.0 V, CANL ≈ 1.0–1.5 V (differential ≈ 2.0 V)
- Expected termination resistance across CANH–CANL: ~60 ohms (two 120Ω terminators in parallel)
- Typical CAN bus speeds: commonly 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- TCM supply voltage (Key ON): battery voltage ~12 V; ground continuity to chassis
Diagnostic algorithm
- Verify the U0101 code and capture freeze-frame data and any related U-codes. Note if code is intermittent.
- Confirm battery state and reliable power supply. Charge or connect a stable battery if voltage is low.
- Try to communicate with the TCM using a manufacturer-level scan tool. If tool cannot see TCM, confirm which modules are present on the bus.
- Inspect fuses and relays for the TCM and replace any blown items. Re-test communication after replacement.
- Visually inspect and disconnect the TCM connector(s). Check pins for corrosion, damage, or pushed-out terminals. Re-seat securely.
- Measure power and ground at the TCM connector. Repair open feeds or poor grounds before replacing modules.
- With ignition ON, measure CANH and CANL at the TCM and at the PCM/gateway. Compare voltages and waveform integrity using an oscilloscope if available.
- Check termination resistance (with power off) between CANH and CANL. If not near expected ~60 ohms, isolate segments to locate missing/extra terminators or an open circuit.
- Isolate wiring faults by disconnecting other nodes or harness branches and re-check bus presence. Use backprobing and continuity checks to find opens or shorts.
- If short to battery or ground is suspected, use a current-limited test lamp or bench supply and isolate sections until the short is located and repaired.
- After wiring/connectors are repaired, clear codes and verify TCM communication. Perform a road test to ensure the issue does not return.
- Replace or reprogram the TCM only after confirming the network and power/ground are good. Follow OEM programming and configuration procedures if replacement is required.
Likely causes
- Damaged or disconnected CANH/CANL wiring at the harness or connector
- Power or ground circuit fault at the TCM (blown fuse, open feed, bad ground)
- Corroded/poor connector pin preventing communication
- Short to battery or ground on the CAN bus (shorted CANH or CANL)
- Faulty TCM or gateway module (replace only after wiring verified)
Fault status
Status
U0101 — Lost Communication With TCM: The Transmission Control Module is not responding on the vehicle communication bus. Possible causes include CAN wiring faults, lack of TCM power/ground, missing termination, or a failed module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email
Code
U0101
ISUZU
U — Network/User
Lost Communication with TCM
Views:
UK: 25
EN: 43
RU: 60
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between TCM and other modules
- Corroded or loose connector at the TCM or intermediate connector
- No power (battery/ignition feed) or poor ground to the TCM
- Failed TCM (internal electronics or firmware) or failed gateway/module
- Missing or faulty CAN bus termination resistor
- Low battery voltage or intermittent supply
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
- Transmission malfunction messages or 'Service Transmission' message in cluster
- No shifting, default/limp transmission behavior or stuck in one gear
- Unable to communicate with TCM using diagnostic scan tool
- Related systems that rely on TCM data may show faults or degraded function
- Intermittent or permanent loss of gear indicator or shift selection display
What to check
- Read and record all current and pending U-codes and freeze frame data with a scan tool
- Attempt to communicate with the TCM with a diagnostic tool at key ON and engine running
- Check battery voltage (should be ~12–14V during testing) and note any drops under cranking
- Inspect and verify fuses and relays that supply power to the TCM and gateway
- Visually inspect TCM connectors and harness for corrosion, bent pins, water damage, or loose terminals
- Perform a wiggle test on harness and connectors while watching for communication loss
Signal parameters
- CAN bus idle (recessive) voltages: CANH ≈ 2.5–2.7 V, CANL ≈ 2.5–2.3 V (node-dependent)
- CAN bus dominant bit voltages: CANH ≈ 3.5–4.0 V, CANL ≈ 1.0–1.5 V (differential ≈ 2.0 V)
- Expected termination resistance across CANH–CANL: ~60 ohms (two 120Ω terminators in parallel)
- Typical CAN bus speeds: commonly 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- TCM supply voltage (Key ON): battery voltage ~12 V; ground continuity to chassis
Diagnostic algorithm
- Verify the U0101 code and capture freeze-frame data and any related U-codes. Note if code is intermittent.
- Confirm battery state and reliable power supply. Charge or connect a stable battery if voltage is low.
- Try to communicate with the TCM using a manufacturer-level scan tool. If tool cannot see TCM, confirm which modules are present on the bus.
- Inspect fuses and relays for the TCM and replace any blown items. Re-test communication after replacement.
- Visually inspect and disconnect the TCM connector(s). Check pins for corrosion, damage, or pushed-out terminals. Re-seat securely.
- Measure power and ground at the TCM connector. Repair open feeds or poor grounds before replacing modules.
- With ignition ON, measure CANH and CANL at the TCM and at the PCM/gateway. Compare voltages and waveform integrity using an oscilloscope if available.
- Check termination resistance (with power off) between CANH and CANL. If not near expected ~60 ohms, isolate segments to locate missing/extra terminators or an open circuit.
- Isolate wiring faults by disconnecting other nodes or harness branches and re-check bus presence. Use backprobing and continuity checks to find opens or shorts.
- If short to battery or ground is suspected, use a current-limited test lamp or bench supply and isolate sections until the short is located and repaired.
- After wiring/connectors are repaired, clear codes and verify TCM communication. Perform a road test to ensure the issue does not return.
- Replace or reprogram the TCM only after confirming the network and power/ground are good. Follow OEM programming and configuration procedures if replacement is required.
Likely causes
- Damaged or disconnected CANH/CANL wiring at the harness or connector
- Power or ground circuit fault at the TCM (blown fuse, open feed, bad ground)
- Corroded/poor connector pin preventing communication
- Short to battery or ground on the CAN bus (shorted CANH or CANL)
- Faulty TCM or gateway module (replace only after wiring verified)
Fault status
Status
U0101 — Lost Communication With TCM: The Transmission Control Module is not responding on the vehicle communication bus. Possible causes include CAN wiring faults, lack of TCM power/ground, missing termination, or a failed module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email
Code
U0101
LAND ROVER
U — Network/User
Lost communication with the transmission control module
Views:
UK: 11
EN: 29
RU: 46
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between TCM and other modules
- Corroded or loose connector at the TCM or intermediate connector
- No power (battery/ignition feed) or poor ground to the TCM
- Failed TCM (internal electronics or firmware) or failed gateway/module
- Missing or faulty CAN bus termination resistor
- Low battery voltage or intermittent supply
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
- Transmission malfunction messages or 'Service Transmission' message in cluster
- No shifting, default/limp transmission behavior or stuck in one gear
- Unable to communicate with TCM using diagnostic scan tool
- Related systems that rely on TCM data may show faults or degraded function
- Intermittent or permanent loss of gear indicator or shift selection display
What to check
- Read and record all current and pending U-codes and freeze frame data with a scan tool
- Attempt to communicate with the TCM with a diagnostic tool at key ON and engine running
- Check battery voltage (should be ~12–14V during testing) and note any drops under cranking
- Inspect and verify fuses and relays that supply power to the TCM and gateway
- Visually inspect TCM connectors and harness for corrosion, bent pins, water damage, or loose terminals
- Perform a wiggle test on harness and connectors while watching for communication loss
Signal parameters
- CAN bus idle (recessive) voltages: CANH ≈ 2.5–2.7 V, CANL ≈ 2.5–2.3 V (node-dependent)
- CAN bus dominant bit voltages: CANH ≈ 3.5–4.0 V, CANL ≈ 1.0–1.5 V (differential ≈ 2.0 V)
- Expected termination resistance across CANH–CANL: ~60 ohms (two 120Ω terminators in parallel)
- Typical CAN bus speeds: commonly 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- TCM supply voltage (Key ON): battery voltage ~12 V; ground continuity to chassis
Diagnostic algorithm
- Verify the U0101 code and capture freeze-frame data and any related U-codes. Note if code is intermittent.
- Confirm battery state and reliable power supply. Charge or connect a stable battery if voltage is low.
- Try to communicate with the TCM using a manufacturer-level scan tool. If tool cannot see TCM, confirm which modules are present on the bus.
- Inspect fuses and relays for the TCM and replace any blown items. Re-test communication after replacement.
- Visually inspect and disconnect the TCM connector(s). Check pins for corrosion, damage, or pushed-out terminals. Re-seat securely.
- Measure power and ground at the TCM connector. Repair open feeds or poor grounds before replacing modules.
- With ignition ON, measure CANH and CANL at the TCM and at the PCM/gateway. Compare voltages and waveform integrity using an oscilloscope if available.
- Check termination resistance (with power off) between CANH and CANL. If not near expected ~60 ohms, isolate segments to locate missing/extra terminators or an open circuit.
- Isolate wiring faults by disconnecting other nodes or harness branches and re-check bus presence. Use backprobing and continuity checks to find opens or shorts.
- If short to battery or ground is suspected, use a current-limited test lamp or bench supply and isolate sections until the short is located and repaired.
- After wiring/connectors are repaired, clear codes and verify TCM communication. Perform a road test to ensure the issue does not return.
- Replace or reprogram the TCM only after confirming the network and power/ground are good. Follow OEM programming and configuration procedures if replacement is required.
Likely causes
- Damaged or disconnected CANH/CANL wiring at the harness or connector
- Power or ground circuit fault at the TCM (blown fuse, open feed, bad ground)
- Corroded/poor connector pin preventing communication
- Short to battery or ground on the CAN bus (shorted CANH or CANL)
- Faulty TCM or gateway module (replace only after wiring verified)
Fault status
Status
U0101 — Lost Communication With TCM: The Transmission Control Module is not responding on the vehicle communication bus. Possible causes include CAN wiring faults, lack of TCM power/ground, missing termination, or a failed module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualLand Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualLand Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop ManualYour experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email
Code
U0101
MERCEDES-BENZ
U — Network/User
Lost Communication with TCM
Views:
UK: 30
EN: 59
RU: 63
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between TCM and other modules
- Corroded or loose connector at the TCM or intermediate connector
- No power (battery/ignition feed) or poor ground to the TCM
- Failed TCM (internal electronics or firmware) or failed gateway/module
- Missing or faulty CAN bus termination resistor
- Low battery voltage or intermittent supply
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
- Transmission malfunction messages or 'Service Transmission' message in cluster
- No shifting, default/limp transmission behavior or stuck in one gear
- Unable to communicate with TCM using diagnostic scan tool
- Related systems that rely on TCM data may show faults or degraded function
- Intermittent or permanent loss of gear indicator or shift selection display
What to check
- Read and record all current and pending U-codes and freeze frame data with a scan tool
- Attempt to communicate with the TCM with a diagnostic tool at key ON and engine running
- Check battery voltage (should be ~12–14V during testing) and note any drops under cranking
- Inspect and verify fuses and relays that supply power to the TCM and gateway
- Visually inspect TCM connectors and harness for corrosion, bent pins, water damage, or loose terminals
- Perform a wiggle test on harness and connectors while watching for communication loss
Signal parameters
- CAN bus idle (recessive) voltages: CANH ≈ 2.5–2.7 V, CANL ≈ 2.5–2.3 V (node-dependent)
- CAN bus dominant bit voltages: CANH ≈ 3.5–4.0 V, CANL ≈ 1.0–1.5 V (differential ≈ 2.0 V)
- Expected termination resistance across CANH–CANL: ~60 ohms (two 120Ω terminators in parallel)
- Typical CAN bus speeds: commonly 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- TCM supply voltage (Key ON): battery voltage ~12 V; ground continuity to chassis
Diagnostic algorithm
- Verify the U0101 code and capture freeze-frame data and any related U-codes. Note if code is intermittent.
- Confirm battery state and reliable power supply. Charge or connect a stable battery if voltage is low.
- Try to communicate with the TCM using a manufacturer-level scan tool. If tool cannot see TCM, confirm which modules are present on the bus.
- Inspect fuses and relays for the TCM and replace any blown items. Re-test communication after replacement.
- Visually inspect and disconnect the TCM connector(s). Check pins for corrosion, damage, or pushed-out terminals. Re-seat securely.
- Measure power and ground at the TCM connector. Repair open feeds or poor grounds before replacing modules.
- With ignition ON, measure CANH and CANL at the TCM and at the PCM/gateway. Compare voltages and waveform integrity using an oscilloscope if available.
- Check termination resistance (with power off) between CANH and CANL. If not near expected ~60 ohms, isolate segments to locate missing/extra terminators or an open circuit.
- Isolate wiring faults by disconnecting other nodes or harness branches and re-check bus presence. Use backprobing and continuity checks to find opens or shorts.
- If short to battery or ground is suspected, use a current-limited test lamp or bench supply and isolate sections until the short is located and repaired.
- After wiring/connectors are repaired, clear codes and verify TCM communication. Perform a road test to ensure the issue does not return.
- Replace or reprogram the TCM only after confirming the network and power/ground are good. Follow OEM programming and configuration procedures if replacement is required.
Likely causes
- Damaged or disconnected CANH/CANL wiring at the harness or connector
- Power or ground circuit fault at the TCM (blown fuse, open feed, bad ground)
- Corroded/poor connector pin preventing communication
- Short to battery or ground on the CAN bus (shorted CANH or CANL)
- Faulty TCM or gateway module (replace only after wiring verified)
Fault status
Status
U0101 — Lost Communication With TCM: The Transmission Control Module is not responding on the vehicle communication bus. Possible causes include CAN wiring faults, lack of TCM power/ground, missing termination, or a failed module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email
Code
U0101
OPEL
U — Network/User
CAN-Bus no Communication with Transmission Control Module
Views:
UK: 7
EN: 16
RU: 25
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between TCM and other modules
- Corroded or loose connector at the TCM or intermediate connector
- No power (battery/ignition feed) or poor ground to the TCM
- Failed TCM (internal electronics or firmware) or failed gateway/module
- Missing or faulty CAN bus termination resistor
- Low battery voltage or intermittent supply
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
- Transmission malfunction messages or 'Service Transmission' message in cluster
- No shifting, default/limp transmission behavior or stuck in one gear
- Unable to communicate with TCM using diagnostic scan tool
- Related systems that rely on TCM data may show faults or degraded function
- Intermittent or permanent loss of gear indicator or shift selection display
What to check
- Read and record all current and pending U-codes and freeze frame data with a scan tool
- Attempt to communicate with the TCM with a diagnostic tool at key ON and engine running
- Check battery voltage (should be ~12–14V during testing) and note any drops under cranking
- Inspect and verify fuses and relays that supply power to the TCM and gateway
- Visually inspect TCM connectors and harness for corrosion, bent pins, water damage, or loose terminals
- Perform a wiggle test on harness and connectors while watching for communication loss
Signal parameters
- CAN bus idle (recessive) voltages: CANH ≈ 2.5–2.7 V, CANL ≈ 2.5–2.3 V (node-dependent)
- CAN bus dominant bit voltages: CANH ≈ 3.5–4.0 V, CANL ≈ 1.0–1.5 V (differential ≈ 2.0 V)
- Expected termination resistance across CANH–CANL: ~60 ohms (two 120Ω terminators in parallel)
- Typical CAN bus speeds: commonly 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- TCM supply voltage (Key ON): battery voltage ~12 V; ground continuity to chassis
Diagnostic algorithm
- Verify the U0101 code and capture freeze-frame data and any related U-codes. Note if code is intermittent.
- Confirm battery state and reliable power supply. Charge or connect a stable battery if voltage is low.
- Try to communicate with the TCM using a manufacturer-level scan tool. If tool cannot see TCM, confirm which modules are present on the bus.
- Inspect fuses and relays for the TCM and replace any blown items. Re-test communication after replacement.
- Visually inspect and disconnect the TCM connector(s). Check pins for corrosion, damage, or pushed-out terminals. Re-seat securely.
- Measure power and ground at the TCM connector. Repair open feeds or poor grounds before replacing modules.
- With ignition ON, measure CANH and CANL at the TCM and at the PCM/gateway. Compare voltages and waveform integrity using an oscilloscope if available.
- Check termination resistance (with power off) between CANH and CANL. If not near expected ~60 ohms, isolate segments to locate missing/extra terminators or an open circuit.
- Isolate wiring faults by disconnecting other nodes or harness branches and re-check bus presence. Use backprobing and continuity checks to find opens or shorts.
- If short to battery or ground is suspected, use a current-limited test lamp or bench supply and isolate sections until the short is located and repaired.
- After wiring/connectors are repaired, clear codes and verify TCM communication. Perform a road test to ensure the issue does not return.
- Replace or reprogram the TCM only after confirming the network and power/ground are good. Follow OEM programming and configuration procedures if replacement is required.
Likely causes
- Damaged or disconnected CANH/CANL wiring at the harness or connector
- Power or ground circuit fault at the TCM (blown fuse, open feed, bad ground)
- Corroded/poor connector pin preventing communication
- Short to battery or ground on the CAN bus (shorted CANH or CANL)
- Faulty TCM or gateway module (replace only after wiring verified)
Fault status
Status
U0101 — Lost Communication With TCM: The Transmission Control Module is not responding on the vehicle communication bus. Possible causes include CAN wiring faults, lack of TCM power/ground, missing termination, or a failed module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email