OBD-II trouble code
B1602: PATS Received Invalid Format Of Key-Code From Ignition Key Transponder
Ford's Passive Anti-Theft System read only a partial or garbled code from the key transponder. It usually points to interference at the ignition or a marginal/unapproved key rather than a dead key.
Quick facts
- System
- Body
- Category
- Anti-Theft / Immobilizer
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $0 – $350
- DIY difficulty
- Intermediate DIY
What does B1602 mean?
B1602 is a manufacturer-specific Ford body (B) code: 'PATS Received Invalid Format Of Key-Code From Ignition Key Transponder.' It sits between its two siblings: where B1600 means no transponder was read at all and B1601 means a complete but unrecognized code was read, B1602 means a PARTIAL or malformed code came back. The antenna energized the chip and something answered, but the message was incomplete or corrupted, so PATS can't trust it and won't authorize a start.
The classic cause is interference right at the ignition. A second transponder key, a fuel-purchase transponder (such as an old Speedpass), or a cluster of large metal objects on the key ring can distort the low-frequency exchange between the antenna ring and the chip, so only part of the code gets through. Aftermarket remote-start equipment tapped into the ignition circuit can do the same. A marginal, damaged, or unapproved (non-Ford-family) chip that answers weakly is the other common source. Because the fault can originate at either the key or the transceiver, both are suspects.
The practical effect is a crank-no-start, often intermittent — it may start on one attempt and fail on the next as the interference comes and goes — usually with a flashing theft/security light. The good news is that the cheapest fixes (stripping the key ring down to one key, using an approved key) resolve a large share of B1602 cases.
Common causes
- Interference at the ignition from a second transponder key or a fuel-payment fob on the ring
- Large metal objects crowding the key near the antenna ring
- Aftermarket remote-start or anti-theft wiring tapped into the ignition circuit
- Marginal, cracked, or weak transponder chip returning an incomplete code
- Unapproved or wrong-family aftermarket key the system can't cleanly read
- Failing transceiver antenna ring, or a poor connection in its circuit
Symptoms
- Engine cranks but won't start, frequently on an intermittent basis
- Flashing theft/security indicator in the instrument cluster
- Starts reliably only after other keys/metal objects are removed from the ring
- No driveability problem once a clean read is achieved
Diagnostic steps
- 1.Take every other transponder key, fuel-payment fob, and heavy metal object off the ring so only the one key is at the lock, then retry — this resolves a large share of B1602 cases for free.
- 2.Confirm the key is an approved PATS type (Ford/Motorcraft, Strattec, ILCO, Rotunda, HUF, or Valeo); swap to a known-good approved key if possible.
- 3.If an aftermarket remote starter or alarm is installed, consider that it may be corrupting the transponder exchange; test with it bypassed if practical.
- 4.Scan PATS and confirm B1602 specifically (partial read) versus B1600 (no read) or B1601 (unrecognized code) to keep the diagnosis on track.
- 5.Inspect the transceiver antenna ring around the ignition cylinder for proper seating and a clean connector.
- 6.If interference and key are ruled out, test the transceiver and its wiring per the service procedure — a weak antenna can garble the code.
- 7.After the repair, verify several consecutive clean starts, since B1602 is often intermittent.
Repair cost
$0 – $350
Many B1602 cases cost nothing — removing extra keys and metal from the ring or switching to an approved key fixes it. If a marginal key is at fault, a replacement transponder key runs $60-$250. A failing transceiver antenna or wiring repair is usually modest; aftermarket remote-start interference may require a return trip to the installer. Because the fix is often free, confirm interference and key quality before buying parts.
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.
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.