U1600 – Electronic key-immobiliser system fault (Fiat, Alpha Romeo, Audi, Nissan)

Akindayini Temiloluwa

By Akindayini Temiloluwa (Contact Me)
Last Updated 2022-04-25
Automotive mechanic

CodeFault LocationProbable Cause
U1600 Electronic key-immobiliser system fault (Fiat, Alpha Romeo, Audi, Nissan)
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Wiring, Key fob battery, Incorrectly programmed key fob, ECU

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What Does Code U1600 Mean?

The U1600 Diagnostic Trouble Code (DTC) stands for the key-immobilizer System fault. You will most likely get the fault code due to a failed key-immobilizer. You can see the electronic key immobilizer as an anti-theft system installed in your vehicle to prevent the unauthorized start of your car. U1600 error code is a manufacturer specific DTC error on Fiat,  Alpha Romeo, Audi, and Nissan cars. 

The immobilizer system became mandatory in 1998 and reduced car theft by nearly 40%, a significant reason I would advise readers here today not to bypass the system but rather fix the issue. 

To fix this fault code, let’s take a good look at how the electronic key immobilizer system works and what causes the DTC error to show on your dashboard. First off, you would notice the warning light on your car’s dashboard. It is usually in the form of a blinking or static key-light. This would be followed by the car refusing to start.

The immobilizer makes use of two key components, which are the transponder and the receiver. The transponder key is a key with a chip that sends out a signal containing a code.  This key has the power to start the car by using its unique code programmed into the chip to disable the device security and anti-theft system. The receiver, on the other hand is located in the vehicle and reads the signals received from the key. 

So, when you want to start your car, you use your key. Once the key is inserted into the car and turned in the right position to start the vehicle, signals are sent to the receiver. In turn, the receiver reads the signals, and then if it is correct, the immobilizer will send a signal to the Engine Control Unit to start the engine. 

When the key-immobilizer is faulty or when there is an attempt to start the car using the wrong key, the U1600 code gets triggered. The immobilizer works hand-in-hand with the Powertrain Control Module (PCM) and the Engine Control Module (ECM). Once the wrong key starts the car, data is sent to the ECM stating that the wrong key is being used. Once the code is incorrect, the ECM will not allow the vehicle to start. Also, once it does not get the correct code, the PCM will throw off a U1600 code.

The same case happens with a faulty immobilizer. A bad or faulty immobilizer can not successfully read the code collected from the ignition key. With this, it can not send signals to the PCM and ECM. Once this happens, the car cannot start, and therefore a code U1600 is triggered and comes with a key light. 

Where is the U1600 sensor located?

The Electric key immobilizer is of two parts: the transponder and receiver. Without each other, the immobilizer would be incomplete. The transponder of the immobilizer is located in the ignition section of the car, just at the right side of the steering wheel. It is designed with a chip programmed to contain a security code that communicates with the receiver. 

On the other hand, the receiver is not in your car key. It is located in your car’s ECU (Engine control unit ). Its location is to facilitate quick response, especially during ignition. Together with the key, this forms the total Immobilizer system. A fault in any of these components results in the U1600 fault code and key-warning light you see on your Fiat dashboard.

What are the common causes of code U1600?

You will most likely get the U1600 DTC and the immobilizer warning light if any of the four components that make up the immobilizer system is damaged. This will include the transponder, receiver, ECU, and car key. Whenever you get the warning light, you should inspect the four components. 

Other factors that could cause the U1600 fault code include:

  • Damaged wires and connection
  • A dead key Fob Battery
  • Damaged ECU
  • Incorrectly programmed key fob

What are the symptoms of code U1600?

The U1600 Electronic key-immobilizer system fault is a very frustrating DTC fault because it affects the entire function of the car. In most cases, the car will refuse to start, or unlock, making it one of the most dreaded codes of a Fiat owner. The following are the symptoms you would notice if your car suffers from the U1600 fault code:

  • Triggered Immobilizer warning light
  • Triggered Check engine light (in some cases)
  • Failed Ignition
  • Car refusal to unlock

Since the immobilizer was designed to keep intruding people from starting your car, the car will automatically try to protect itself if a wrong key is used or there is a fault in the Immobilizer system.

Codes Related to U1600

The following are some related codes that may appear with the U1600 fault code on your OBD II scanner:

P0648- Immobiliser lamp control circuit fault

The P0648 generic code is stored where the PCM  detects a faulty or burnt immobiliser lamp. This would be followed  by the stored code and a check engine warning light. The abnormal reading   in the immobiliser circuit may also be as a result of bad wiring which may cause the code to be stored.

P0513- Incorrect immobilizer

The code is similar to the U1600 fault code as they both deal with the malfunction of the immobilizer. But unlike the U1600, this is a generic code trouble code that can be seen in all vehicles. The result is the inability of the car to start or unlock.

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