B1602 — PATS Received Invalid Format Of Key-Code From Ignition Key Transponder #

The code title may vary depending on the vehicle manufacturer. Below are known variations of this code’s description:

• Ford: PATS Received Invalid Format Of Key-Code From Ignition Key Transponder
• Lincoln: PATS Key Code Not Recognized
• Mazda: Incorrect Key Code Received from Transponder
• Mercury: PATS Key Transponder Code Not Accepted

Summary of code B1602 #

B1602 is a diagnostic trouble code (DTC) tied to the vehicle’s immobilizer system, specifically the PATS (Passive Anti-Theft System). This code indicates that the vehicle’s immobilizer module has received a key-code signal from the ignition key’s transponder, but the format of that code is invalid or not recognized. The transponder is a tiny chip embedded in the key head that communicates with the car to verify if the key is authorized. When this process fails, the immobilizer typically prevents the engine from starting, acting as a vital anti-theft mechanism. This DTC is most commonly encountered on Ford family vehicles, but other OEMs (Original Equipment Manufacturers) using similar anti-theft technologies may also report it.

Frequent symptoms for code B1602 #

When B1602 is logged, the most obvious symptom is a failure to start or crank the engine. Depending on the vehicle and system, you might also notice warning lights or error messages related to security or the immobilizer. These symptoms are frustrating, especially if they strike unexpectedly, but they are key clues to narrow down the issue.

• Engine will not start (no crank or no start condition)
• Security or immobilizer warning light illuminated on dashboard
• Intermittent starting problems (vehicle starts sometimes but not always)
• Anti-theft message displayed in instrument cluster
• Possible rapid flashing of the security indicator lamp (SIL)

Most likely causes for code B1602 #

B1602 is triggered most often by issues with the key or the transponder communication, but it may also relate to wiring or the immobilizer module itself. Some causes are much more common than others, so prioritizing your checks can save time and frustration.

1. Unprogrammed, damaged, or incorrect ignition key
2. Faulty or weak transponder chip inside the key
3. Interference or poor communication between key and immobilizer antenna
4. Problems with the immobilizer antenna ring (PATS antenna)
5. Corroded, loose, or damaged wiring/connectors related to the PATS system
6. Faulty immobilizer (PATS) control module

Step-by-step diagnostic for code B1602 #

Diagnosing B1602 requires a logical, patient approach. Start with the basics and move to more complex possibilities only if necessary. Having a second programmed key can be extremely helpful for comparison. Here’s a stepwise guide:

1. Check for additional trouble codes — Other codes may provide more context or pinpoint related faults.
2. Verify the key — Use a known, correctly programmed spare key if possible. Does the car start with it?
3. Visually inspect the key — Look for physical damage, wear, or evidence of tampering.
4. Check for radio interference — Move other electronic devices (cell phones, tags, other keys) away from the ignition area.
5. Test the PATS antenna ring — Inspect for physical damage or corrosion, especially around the ignition cylinder.
6. Inspect wiring and connectors — Look for corrosion, loose pins, or broken wires in the immobilizer circuit.
7. Attempt to reprogram or relearn the key — Follow OEM procedures using a compatible scan tool.
8. Test or replace the immobilizer module — Only after all other steps have been exhausted and following OEM guidelines.

Possible repairs for code B1602 #

The right repair depends on what you find during diagnostics, but most solutions focus on either the key or the communication path between key and immobilizer.

• Replace or reprogram the ignition key — If the key is unprogrammed, lost synchronization, or damaged, a new key with correct programming is required.
• Replace the transponder chip — If the chip inside the key is faulty, replacement is necessary.
• Repair or replace the PATS antenna ring — If the antenna around the ignition lock is damaged, this can interrupt signal transmission.
• Clean or repair wiring and connectors — Fix corroded, loose, or broken connections in the immobilizer circuit.
• Replace the immobilizer (PATS) control module — Rare, but sometimes necessary if the module is not functioning or storing corrupted data.

Can you drive with code B1602? #

No, you usually cannot drive with code B1602 active. This code generally prevents the engine from starting as a security measure. Even if the issue is intermittent, you risk being stranded if you ignore it. If the car does manage to start, it’s often purely coincidental and not reliable. The immobilizer system is designed specifically to prevent unauthorized operation, so resolving the cause of the code is essential before attempting regular use.

Vehicles most commonly affected by code B1602 #

While B1602 is most frequently found in Ford group vehicles, other manufacturers using similar PATS technology may also report it. The following vehicles are especially prone to this code:

• Ford Focus (2000–2011)
• Ford Fiesta (1999–2012)
• Ford Transit and Transit Connect (2002–2014)
• Ford Mondeo (2001–2007)
• Lincoln Town Car (2000–2010)
• Mercury Grand Marquis (2000–2011)
• Mazda Tribute (2001–2008)
• Some Jaguar and Land Rover models with Ford-based PATS

Common mistakes & best practices for code B1602 #

Misdiagnosis is common with immobilizer-related codes like B1602. Technicians and drivers often overlook simple causes or jump to expensive repairs. Here are pitfalls to avoid and tips for success:

• Assuming the immobilizer module is faulty before testing the key and antenna
• Neglecting to try a second, correctly programmed key
• Overlooking the role of radio frequency interference from other electronic devices
• Failing to check for damaged or corroded wiring/connectors around the ignition cylinder
• Skipping the OEM-recommended key relearn or programming procedure
• Not verifying that all keys in use are properly programmed to the vehicle

Express FAQ for code B1602 #

Here are answers to some quick, common questions about B1602:

• Can I just replace the key battery to fix B1602?
  No. Most ignition key transponders used for immobilizer systems do not have a replaceable battery. B1602 typically points to a programming or chip issue, not a battery problem.
• Can a locksmith fix code B1602?
  Yes, a professional automotive locksmith with the right tools can often diagnose and reprogram keys or replace faulty transponders, sometimes at a lower cost than a dealership.
• What does PATS mean?
  PATS stands for Passive Anti-Theft System, a security feature that uses a transponder chip in the key and an immobilizer module to prevent unauthorized engine starts.
• If I clear the code, will my car start?
  Clearing the code alone will not resolve the starting issue; you must fix the underlying cause for successful engine start.