What Does P1602 Mean?
This code indicates a communication error between the vehicle's immobilizer system and the Powertrain Control Module. The immobilizer must authenticate the ignition key's transponder before the PCM will enable fuel injection and ignition. A communication failure between these systems may prevent the engine from starting or cause it to stall shortly after starting, as the PCM cannot verify the key is authorized.
Safety Warning
The vehicle may not start or may stall shortly after starting if the immobilizer cannot authenticate. While this prevents theft, it can also strand the vehicle owner in an unsafe location. This is not a driving safety issue per se, but a reliability concern.
Common Causes
25%
Faulty immobilizer antenna ring around the ignition cylinder
25%
Damaged or degraded key transponder chip
20%
Wiring fault between the immobilizer module and PCM
15%
Failed immobilizer control module
15%
PCM immobilizer communication circuit fault or key not properly registered
Diagnostic Steps
1
Attempt to start the vehicle with a second known-good registered key; if it starts, the first key's transponder may be faulty.
2
Check if the immobilizer warning light on the dashboard behaves normally—rapid flashing usually indicates authentication failure.
3
Inspect the ignition cylinder antenna ring connector and wiring for damage or disconnection.
4
Use a manufacturer-specific scan tool to query the immobilizer module for its status and registered key count.
5
Check the communication wiring between the immobilizer module and PCM for continuity and proper voltage levels.
6
If a module has been recently replaced, it may need to be re-registered or programmed to the vehicle's security system.
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
This code indicates a communication error between the vehicle's immobilizer system and the Powertrain Control Module. The immobilizer must authenticate the ignition key's transponder before the PCM will enable fuel injection and ignition. A communication failure between these systems may prevent the...
The most common cause of P1602 (Immobilizer System Communication Error with Powertrain Control Module) is: Faulty immobilizer antenna ring around the ignition cylinder
Typical repair costs for P1602 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle may not start or may stall shortly after starting if the immobilizer cannot authenticate. While this prevents theft, it can also strand the vehicle owner in an unsafe location. This is not a driving safety issue per se, but a reliability concern.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1602 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Immobilizer / Anti-Theft System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
