A weak or dead battery in the key fob transponder, preventing the immobilizer from reading the key; A faulty immobilizer receiver coil around the ignition switch that cannot pick up the key signal; Damaged or corroded wiring between the immobilizer module and the ECM; A failed immobilizer module or a fault in its internal memory; An ECM that has lost its immobilizer pairing data or has an internal fault; Use of an unprogrammed or aftermarket key that the immobilizer does not recognize; A poor ground connection at the immobilizer module or ECM

DTC codes / Mazda codes / P1624

P1624 · MazdaImmobilizer System Fault

Q: What does code P1624 mean?

Immobilizer System Fault. P1624 on a Mazda means the engine control module (ECM) has logged a fault in the immobilizer system, the anti-theft circuit that verifies the key before allowing the engine to start. The ECM detected a mismatch or communication failure between the key transponder, the immobilizer receiver, and the ECM itself, so it stored this code and may prevent the engine from cranking or running.

P1624 on a Mazda means the engine control module (ECM) has logged a fault in the immobilizer system, the anti-theft circuit that verifies the key before allowing the engine to start. The ECM detected a mismatch or communication failure between the key transponder, the immobilizer receiver, and the ECM itself, so it stored this code and may prevent the engine from cranking or running.

SystemPowertrain

Code typeMazda specific

SeverityMedium

Fix difficultyProfessional

AreaComputer and output circuits

Symptoms you may notice

The engine cranks but will not start, or it starts and stalls immediately
The security or immobilizer warning light stays on or flashes while the key is in the ignition
The engine may start normally on some attempts and fail on others, especially with a different key
A no-crank condition where the starter does not engage at all
Often no symptoms besides the warning light if the fault is intermittent
The remote keyless entry may stop working or the key may not be recognized

Common causes, most likely first

A weak or dead battery in the key fob transponder, preventing the immobilizer from reading the key
A faulty immobilizer receiver coil around the ignition switch that cannot pick up the key signal
Damaged or corroded wiring between the immobilizer module and the ECM
A failed immobilizer module or a fault in its internal memory
An ECM that has lost its immobilizer pairing data or has an internal fault
Use of an unprogrammed or aftermarket key that the immobilizer does not recognize
A poor ground connection at the immobilizer module or ECM

How to diagnose and fix it

Check the key fob battery and try a second known-good key to see if the fault follows the key
Inspect the immobilizer receiver coil and its connector for corrosion or physical damage
Scan all modules for stored codes and check live data for immobilizer communication status
Verify battery voltage and ground connections at the immobilizer module and ECM
Perform a key relearn or immobilizer pairing procedure with a factory-level scan tool
Replace the immobilizer receiver coil or module if diagnostics confirm it is faulty
If the ECM is at fault, replace and reprogram it to the vehicle's immobilizer system

What most technicians miss on P1624

A weak key fob battery is the most common cause of P1624 on Mazda vehicles, yet many people replace the immobilizer module before checking it.
This code can set from a simple low battery voltage event, so clearing it after charging the battery may be all that is needed if it does not return.
An aftermarket remote starter or alarm installation often disturbs the immobilizer wiring and sets P1624 without any fault in the factory components.
The immobilizer system can set P1624 even when the engine starts fine, because the ECM logs intermittent communication glitches that do not always prevent starting.
A second key that has never been programmed to the vehicle will trigger P1624 every time it is used, which is easy to overlook when diagnosing a no-start.

Can I keep driving with P1624?

If the engine starts and runs normally, you can drive the vehicle to a repair shop, but avoid shutting it off in an unsafe location because it may not restart. If the engine will not start or stalls immediately, do not attempt to drive and have the vehicle towed to a qualified Mazda technician.

Tools that help

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Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.