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Home / DTC / P1603 — Transmission control module communication error electrically programmable read-only programmable memory failure

P1603 — Transmission control module communication error electrically programmable read-only programmable memory failure

Detailed page for trouble code P1603.

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P1603

LAND ROVER P — Powertrain

Transmission control module communication error electrically programmable read-only programmable memory failure

Brand: LAND ROVER
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Corrupted or failed TCM internal memory (EEPROM/ROM)
  • Interrupted or failed software/programming update of TCM
  • Low or unstable battery voltage during module programming
  • Faulty CAN bus wiring, short, open or high resistance (CAN High/Low)
  • Poor power or ground supply to the TCM (fuse, relay, connector, corrosion)
  • Water ingress or physical damage to TCM connector or housing

Symptoms

  • Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
  • Transmission enters limp or restricted mode (reduced shift availability)
  • No communication with TCM when scanned with diagnostic tool (module not responding)
  • Stored related transmission and communication DTCs in TCM, ECM or gateway
  • Erratic or incorrect shifting, loss of certain transmission functions
  • Intermittent faults that appeared after a software update or battery replacement

What to check

  • Read and record all stored DTCs from all vehicle modules (scan for communication faults)
  • Check battery voltage and condition (fully charged, >12.4 V at rest; >11 V cranking) and ensure stable supply during diagnostics
  • Inspect fuses, relays and main power/ground connections for the TCM
  • Visually inspect TCM connector and wiring for corrosion, damage, bent pins or water ingress
  • Check for history of recent TCM reprogramming or software update failures
  • Attempt to communicate with the TCM using a capable dealer-level scan tool and note error messages

Signal parameters

  • Battery/TCM supply voltage (nominal ~12 V at rest, >11 V while cranking)
  • TCM ground continuity (0 Ω relative to chassis)
  • CAN Bus idle voltages: CAN High ≈ 2.5–3.5 V, CAN Low ≈ 1.0–2.5 V (differential ~2 V)
  • CAN bus data activity and dominant/recessive transitions (oscilloscope or advanced scan tool)
  • Module present/response status from diagnostic tool (OK / Not Responding / Bus Off)

Diagnostic algorithm

  1. Record all DTCs, freeze-frame and UID/firmware versions from TCM and other networked modules.
  2. Verify battery state of charge and charging system; charge battery or use stable power supply before further tests.
  3. Inspect and secure TCM power, ground, fuses and relays; repair any poor connections.
  4. Visually inspect TCM connector and harness for corrosion, water ingress, pins pushed back, or broken wires; repair as necessary.
  5. Check CAN bus physical layer: measure CAN High/Low voltages at the TCM connector, confirm proper idle voltages and activity with key ON and while cranking.
  6. If CAN physical layer is good, attempt communication with TCM using factory diagnostic tool; note any programming or response errors.
  7. If module responds but stores memory/programming faults, attempt an official reflash/reprogram using manufacturer tool and latest calibration; ensure stable battery/power during process.
  8. If reprogramming fails repeatedly and wiring/power are confirmed good, consider replacing TCM or sending TCM to a qualified reman/repair service (module-level memory fault).
  9. After repair or reflash, clear codes, perform relearns or adaptations required by manufacturer, and road test to verify normal transmission operation.

Likely causes

  • Failed or corrupted TCM EEPROM after an update attempt
  • Poor battery condition or dropped voltage during reprogramming
  • Damaged or corroded TCM connector or pin(s) affecting communication/power
  • CAN bus wiring fault between TCM and gateway/module

Fault status

⚠️ Status
Transmission control module communication or programmable memory failure — stored when the TCM reports EEPROM/ROM or communication errors (module not responding or failed reprogramming).
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.5-3.0 hours

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413

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