P1612

NATS Chain of ECM-IMMU

Car Fault Codes Nissan Engine computer & electrical

Can you still drive? No, stop right away

Who can fix it? Needs a workshop

Typical repair time 30 minutes – 4 hours

Typical cost SAR 100 to 3,500

What it means

This is a Nissan-specific code for vehicles with NATS; the same number can mean something different on other makes. It means the engine computer (ECM) is not getting a valid reply from the immobilizer unit (IMMU) over the communication line between them, so it cannot verify the key and blocks the engine from running. The cause is usually electrical, such as a wire, connector, power feed or ground to the unit.

Models covered: Nissan (and Infiniti) models with NATS (Nissan Anti-Theft System), mainly around 1999–2008 (e.g. Altima, Maxima, Sentra, Pathfinder, X-Trail).

Symptoms4

The engine does not start, or starts and stalls right away.
The security indicator light stays on or behaves abnormally.
The fault may be intermittent, with the engine starting sometimes and refusing at other times.
It may appear after a collision, water leak or repair work around the dashboard.

Possible causes6

A loose or corroded connector at the immobilizer unit or ECM.
A broken or chafed wire in the communication line between the two units.
Lost power or ground to the immobilizer unit due to a fuse or damaged connection.
A weak battery or unstable voltage during cranking.
A faulty immobilizer unit (IMMU).
A faulty ECM (less common).

How to diagnose5

Check battery voltage during cranking, since low voltage can break communication.
Check the fuses feeding the immobilizer unit and confirm it has power and ground.
Unplug the immobilizer unit and ECM connectors and look for corrosion or loose pins.
Check continuity of the communication line between the units and make sure it is not shorted to ground or power, per the wiring diagram.
Use a Nissan-capable scan tool to check whether the immobilizer unit responds.

How to fix6

Charge or replace a weak battery and clean its terminals.
Replace a blown fuse and repair any power or ground fault.
Clean the connectors and repair the broken or chafed communication wire.
Replace the immobilizer unit if confirmed faulty, then perform initialization and key registration with a Nissan-capable tool.
Replace the ECM if confirmed faulty, then pair it with the immobilizer unit.
Clear the codes and try several starts while gently moving the wiring to confirm an intermittent fault is gone.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low when a fuse, connector or wire is the cause, and rises if a new immobilizer unit or ECM with programming and pairing is needed.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

What is the difference between P1612 and P1611?

P1612 means the two units are not communicating at all, usually an electrical fault. P1611 means they communicate but the IDs do not match, which is usually fixed by pairing.

Why does the engine start sometimes and not others?

An electrical fault in the communication line can be intermittent, such as a loose connector affected by heat or vibration, so it is tested while moving the wiring.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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