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

OBD2 code B1602 flags a problem with the ignition system (PATS received invalid format of key-code from ignition key transponder). Short, gentle driving to a shop is usually possible. Common culprits: worn spark plugs or wrong plug gap, failed ignition coil or coil pack, moisture or oil in the spark plug wells.

body electrical

Is it safe to drive?

Drive with caution Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1602 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ignition system for damage, corrosion, chafing or poor contact.
Subsystem check Swap the coil to another cylinder and see if the fault code follows it.
Subsystem check Inspect spark plugs for wear, oil or carbon tracks and check plug gaps.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1602 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1602 (parts and labor, USD, independent shop rates): Replace an ignition coil: $150–$380; Repair coil wiring or connector: $80–$250; Replace spark plugs: $90–$250. Overall, fixing B1602 usually costs between $80 and $380. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Will B1602 clear itself?

Sometimes B1602 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose B1602 myself?

Start with a scan: confirm B1602, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition system, and verify the suspect component against live data before buying parts.

How much does it cost to fix B1602?

Replace an ignition coil — $150–$380; Repair coil wiring or connector — $80–$250; Replace spark plugs — $90–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What is the most common cause of B1602?

The most common causes are: worn spark plugs or wrong plug gap, failed ignition coil or coil pack, moisture or oil in the spark plug wells.

Is it safe to drive with B1602?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

When your vehicle's computer detects a communication breakdown between the ignition key's transponder chip and the theft-deterrent system, it sets trouble code B1602. The full technical description reads: "PATS Received Invalid Format Of Key-Code From Ignition Key Transponder." This code lives in the body electronics category rather than the engine or transmission systems, which means the issue stems from the security hardware rather than mechanical drivetrain components.

The Passive Anti-Theft System (PATS) relies on a tiny radio-frequency transponder embedded in your ignition key. When you turn the key, the system module sends a coded signal to the chip, which responds with its own unique identifier. If that response arrives in an unexpected format or fails to match what the ECU expects, the security system prevents the engine from starting or running properly. B1602 specifically indicates the transponder's reply was received but corrupted or malformed—different from B1600, which means no signal at all, or B1601, which means the code was correct but wrong for this vehicle.

The engine control unit monitors these security handshakes continuously, even while driving. Once the irregular pattern persists long enough to trigger the fault detection logic, B1602 gets stored in memory alongside a freeze frame snapshot showing engine speed, load, temperature, and vehicle speed at that exact moment. This data proves invaluable during diagnosis because it tells you exactly what conditions provoked the failure.

Symptoms of B1602

Engine refuses to start or starts only after multiple attempts
Intermittent stalling and loss of power under acceleration
Rough idling and cylinder misfires during normal operation
Noticeable increase in fuel consumption compared to normal
Check Engine Light or security warning lamp illuminated on the dash

Common Causes of B1602

Damaged or corroded wiring harness feeding the ignition module
Failed ignition coil, coil pack, or individual cylinder ignition coil
Worn spark plugs with incorrect gap spacing or heavy carbon buildup
Oil or moisture contamination inside the spark plug well or boot
Faulty electrical connector at the ignition coil or PATS module
Defective transponder chip inside the ignition key itself

How to Diagnose B1602

Connect a professional-grade OBD2 scanner and retrieve all stored codes, paying special attention to B1602 and any accompanying P0300-series misfire codes. Save the freeze frame data—it reveals engine conditions when the failure occurred.
Run a manufacturer-specific TSB (Technical Service Bulletin) search using your vehicle's VIN on the automaker's website or NHTSA database. Many B1602 complaints have documented factory fixes or calibration updates.
Perform a thorough visual inspection of all wiring and connectors tied to the ignition coil and anti-theft module. Look for frayed wires, green corrosion deposits, melted insulation near heat sources, and loose or pushed-out pins.
Test the ignition coil's primary and secondary resistance with a multimeter against factory specifications. Swap a suspect coil to another cylinder and clear the code—if the fault moves with the coil, you've found the culprit.
Remove and inspect each spark plug for cracked ceramics, wet oil residue, carbon tracking, or worn electrodes. Measure the gap with a feeler gauge and compare it to the manufacturer's specification.
After addressing the suspected cause, clear the code and complete a full drive cycle that reproduces the freeze frame conditions. If B1602 does not return, the repair is confirmed.

Repair Options and Costs (USD, Independent Shop)

Ignition coil or coil pack replacement: $150–$380 (parts and labor)
Wiring harness repair or connector replacement: $80–$250
Spark plug set replacement: $90–$250

Always start diagnosis with the least expensive components—spark plugs and connectors—before committing to coil or harness repairs.

Total Cost to Fix B1602

For most vehicles, resolving B1602 runs between $80 and $380 depending on which part actually failed. Spark plug replacement sits at the lower end, while coil pack and wiring repairs push toward the higher range. Independent shops typically charge less than dealerships, and many allow you to provide your own parts if you source them separately. The most important investment is an accurate diagnosis before purchasing any components—the fault rarely lives where it first appears.

Can You Drive With B1602?

This code carries a caution severity rating. While the vehicle may still run in some cases, ignition misfires triggered by B1602 can send unburned fuel into the exhaust stream, rapidly overheating and destroying the catalytic converter. If the Check Engine Light flashes rather than stays solid, stop driving immediately and address the problem before damage spreads. Even when the light remains steady, limit heavy loads and hard acceleration until the underlying fault is resolved.