What's the difference between B1601 and B1600?

B1600 means NO transponder was read at all — the antenna energized and heard nothing, so you look at the chip, antenna, wiring, or module. B1601 means a key WAS read cleanly, but its code isn't in the vehicle's memory. That's a programming problem, not a hardware fault. If you have B1601, the fix is almost always to program the key, not to replace parts.

My brand-new key throws B1601 — is the key defective?

Almost certainly not. B1601 with a new key is the system telling you the key has a good, readable chip but hasn't been taught to this car yet. Cutting a key to fit the lock and programming its chip to PATS are two separate steps — a locksmith or dealer must complete the programming step before the car will accept it.

Can I program the key myself to clear B1601?

Sometimes. Many Ford models allow an on-board two-key procedure: if you already have two keys the car accepts, you can add another by cycling the ignition through both within a set time, no tools needed. With only one working key, or none, you'll need a scan tool (or software like FORScan) and a security-access wait, commonly about 10 minutes, to add or erase keys.

Why won't my car take a key that works in my other Ford?

Each vehicle stores its own list of authorized key codes. A key programmed to a different vehicle has a perfectly valid chip, but its code isn't in this car's PATS memory, so you get B1601. The key must be programmed specifically to the vehicle you want to start — keys are not interchangeable between cars even within the same model.

OBD-II trouble code

B1601: PATS Received Incorrect Key-Code From Ignition Key Transponder

Ford's Passive Anti-Theft System read a key, but the key isn't programmed into this vehicle's memory. The engine cranks but won't start until the key is programmed or a recognized key is used.

Quick facts

System: Body
Category: Anti-Theft / Immobilizer
Severity: Medium severity
Drivable: No — stop driving until repaired
Repair cost range: $0 – $250
DIY difficulty: Intermediate DIY

What does B1601 mean?

B1601 is a manufacturer-specific Ford body (B) code: 'PATS Received Incorrect Key-Code From Ignition Key Transponder.' PATS is Ford's Passive Anti-Theft System immobilizer. Unlike its sibling B1600, this code means the system DID read a transponder — the antenna energized the chip and got a complete, valid response — but the code that came back does not match any key stored in the vehicle's PATS memory. In plain terms: a real, readable key was presented, but the car doesn't recognize it.

The most common cause is simply an unprogrammed key: a newly cut key, a replacement, or a key from another vehicle that has a working chip but has never been taught to this car. The key hardware is usually fine — it just needs to be programmed into PATS memory (unless the vehicle already has the maximum number of keys stored, in which case one must be erased first). Less often, B1601 can follow a PCM or module replacement that wiped the key table, or a mismatch after a security relearn was interrupted.

Because PATS immobilizes the engine when it can't authorize a key, the effect is a crank-no-start with a flashing theft/security light. This is a programming/recognition problem, not a wiring or antenna failure — which is exactly why distinguishing B1601 from B1600 (no key read) and B2103 (antenna failure) matters before you spend a dime.

Common causes

Unprogrammed key — newly cut, replacement, or borrowed from another vehicle, never taught to this car
Key programmed to a different vehicle (valid chip, wrong code)
Maximum number of keys already stored, so a new key can't be added until one is erased
PCM or PATS module replaced, wiping or mismatching the stored key table
Security relearn interrupted or not completed after service
Occasionally, a marginal or off-brand chip returning a code the module rejects

Symptoms

Engine cranks normally but will not start
Flashing theft/security indicator in the instrument cluster
Happens specifically with a new or replacement key while the original key still works
No driveability problem once a recognized key is used

Diagnostic steps

1.Try a key you know the car accepts. If it starts, B1601 is confirming that the other key simply isn't programmed to this vehicle.
2.Confirm whether the problem key is new, a replacement, or from another vehicle — any of these need programming into PATS memory.
3.Scan the PATS system and read the exact code: B1601 (incorrect/unrecognized code) is a programming issue, unlike B1600 (no read) or B1602 (partial read).
4.Check how many keys are already programmed; if the vehicle is at its maximum, an existing key must be erased before a new one can be added.
5.If the code appeared after a module or PCM replacement, expect to program all keys and complete the security relearn.
6.Program the key with the correct procedure (on-board two-key method or a scan tool with the security-access wait), then verify start and that the theft light arms normally.

Repair cost

$0 – $250

If you already have a working key and the car supports the on-board two-key procedure, programming a spare can cost nothing. Otherwise, an independent automotive locksmith or dealer typically charges $50-$150 to program a key (often bundled with cutting a new transponder key for $60-$250 total). No parts are needed when the key hardware is fine — this is a programming charge, not a repair.

Estimate your repair

Run the numbers for your vehicle

Open the Repair Cost Estimator with immobilizer key / anti-theft service preselected. Adjust labor rate and vehicle category to fit your situation.

Estimate your repair cost

DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.

Related codes

B1600 B1602 B1213 B2103 P0513