U101A

Code

LAND ROVER U — Network/User

Communication lost with the transmission control module - Multiple bus

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 13 EN: 27 RU: 16

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Page language: EN

Causes

Open, shorted or corroded wiring/connectors on CAN/Multiple bus circuits
Failed or intermittently powered TCM (loss of VBATT or ground)
Faulty gateway/module that routes messages between buses
Missing or damaged CAN/LIN termination resistors
Blown fuse or disabled power/ignition feed to TCM or gateway
Software/firmware mismatch or module programming error

Symptoms

Transmission limp mode or reduced shift functionality
Transmission warning lamp or MIL illuminated
Loss of certain transmission-related functions in instrument cluster or infotainment
No communication with TCM when scanning with a diagnostic tool
Intermittent or permanent DTCs for other modules that rely on TCM data

What to check

Read all stored DTCs and freeze frame with a capable OEM or J2534 scanner
Verify battery voltage is stable (12.4–12.8 V with key off; 13.5–14.5 V with engine running)
Inspect fuses and relays related to TCM, gateway and CAN power feeds
Visually inspect TCM and gateway connectors for corrosion, bent pins, water ingress
Check for aftermarket modules or recent wiring work that may have disturbed bus wiring
Measure CANH/CANL voltages at TCM connector and gateway with key on

Signal parameters

Idle (recessive) CANH ≈ 2.5 V, CANL ≈ 2.5 V (tolerance ±0.5 V)
Dominant CAN state: CANH ≈ 3.5 V, CANL ≈ 1.5 V (differential ≈ 2.0 V)
Termination resistance between CANH and CANL ≈ 60 ohms (two 120Ω in parallel)
Typical gateway/TCM supply voltage: battery nominal 12 V (key on/engine running as above)
Bus baud rates vary by vehicle (commonly 250 kb/s or 500 kb/s for CAN powertrain buses)

Diagnostic algorithm

Capture current and historical DTCs from all modules; note events related to power or bus errors.
Confirm battery state and perform a known-good battery charge if voltage is low.
Inspect and secure grounds and power feeds to the TCM and gateway; swap or wiggle connectors while monitoring communication.
Check relevant fuses/relays and restore any missing power circuits. Re-scan for communication after restoring power.
With ignition on, measure CANH/CANL at the TCM connector and at the gateway/module that interfaces multiple buses. Compare to signal parameters.
With vehicle power off, measure termination resistance across CANH and CANL near the TCM and gateway (expect ~60Ω).
If bus voltages or termination are abnormal, trace wiring harness for shorts to battery/ground or open circuits and repair as needed.
If wiring and power are good but the TCM does not respond, attempt communication at the gateway; if gateway lacks TCM messages, test/replace gateway per OEM procedure.
If intermittent, use an oscilloscope or CAN bus analyzer to capture traffic and identify collisions, noise or missing messages during events.
If module replacement is required, follow manufacturer reprogramming/coding procedures before final verification; clear codes and road test to confirm repair.

Likely causes

Connector or harness damage at TCM or gateway
Faulty TCM power supply (blown fuse, poor battery/ignition feed)
Corroded CAN bus connector or broken shield/ground
Faulty gateway/module that aggregates multiple buses

Fault status

⚠️ Status

U101A — Communication lost with the Transmission Control Module (multiple bus). The vehicle network/gateway is not receiving expected TCM messages within the defined timeout.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours

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U101A — Communication lost with the transmission control module - Multiple bus