Code
P1615
SCION
P — Powertrain
Communication error with immobilizer
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EN: 2
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AI status
Completed
Completed
100%
Causes
- Faulty immobilizer (antitheft) control module
- Loss of communication on CAN/LIN data bus between ECM and immobilizer
- Damaged wiring or poor connector grounds between modules
- Blown fuse or loss of supply to immobilizer
- Faulty ignition key transponder or key programming/coding mismatch
- Battery low voltage or intermittent supply
Symptoms
- Engine will not crank or starts and immediately stalls
- Starter crank allowed but engine does not run
- Security or immobilizer warning lamp illuminated or flashing
- MIL (Check Engine Light) lamp on
- Intermittent no-start conditions
- Key recognition failure messages on dash (if equipped)
What to check
- Scan all modules and record freeze frame and related U-codes (CAN network) and P-codes
- Verify battery voltage is stable (12.4–14.5 V) with engine off and during cranking
- Inspect fuses and relay for immobilizer/powertrain and replace if blown
- Visually inspect wiring harnesses and connectors for corrosion, damage, or loose pins at ECM and immobilizer
- Check for multiple related communication codes (U-codes) on the CAN bus
- Confirm spare or master key operation; test with known-good programmed key if available
Signal parameters
- Battery supply to immobilizer module: ~12–14.5 V (engine on/off as applicable)
- Ground continuity: close to 0 Ω between module ground and chassis ground
- CAN bus idle voltages: CAN High ≈ 2.5–3.5 V, CAN Low ≈ 1.5–2.5 V (typical quiescent ~2.5 V common mode)
- CAN differential when active: >1.0 V peak-to-peak between CAN H and CAN L during data traffic
- Immobilizer antenna coil resistance: check service manual spec (typically a few ohms to low kilo-ohms); open or short indicates fault
- Transponder/key detection: scanner should report key recognized / immobilizer status bits (varies by tool)
Diagnostic algorithm
- Retrieve all stored DTCs and freeze-frame data from ECM, immobilizer and body modules. Note any U-codes (network faults).
- Verify battery condition and terminal connections. Charge battery or use a stable supply before further testing.
- Clear codes and attempt a controlled start. Observe whether P1615 returns and record any accompanying codes.
- Inspect fuses/relays for the immobilizer, body ECU and ECM power; replace suspect fuses and retest.
- Visually inspect connectors and wiring between the immobilizer antenna, immobilizer module and ECM for corrosion, bent pins or damage. Repair as needed.
- Using a scan tool, attempt to communicate with the immobilizer/antitheft unit. If the tool cannot communicate, suspect wiring, power/ground, or module failure.
- Measure CAN High/Low voltages at the immobilizer module connector with key off and during cranking. Look for expected idle voltages and activity. Repair wiring or bus shorts if abnormal.
- Test immobilizer antenna coil resistance and continuity per service manual. If out of spec, replace antenna or harness.
- Verify key recognition: try known-good programmed key(s). If a spare works, reprogram or replace faulty key transponder.
- If wiring, power and keys are good but communication still fails, consult service documentation for immobilizer module bench tests and consider module replacement and security re-learn (may require dealer-level tool).
- After repairs, clear codes and perform multiple start cycles and a road test to confirm fault does not return. Perform immobilizer/ECM relearn procedures if required.
Likely causes
- Open or short in the CAN data lines or poor connector at immobilizer module
- Dead or weak vehicle battery causing intermittent module communications
- Failed immobilizer module or antenna coil
- Faulty or unprogrammed key (spare key not learned)
- Blown/inaccessible fuse for anti-theft or module power
Fault status
Status
P1615 — Communication error with immobilizer: The ECM has detected loss or corruption of communications with the immobilizer/anti-theft control unit. This may prevent key recognition and can disable engine start. Check power, grounds, wiring, CAN bus, key transponder and immobilizer module.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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