OBD-II Diagnostic Trouble Code
B2790 — Coded Ignition Key Malfunction
B2790 is a manufacturer-specific immobilizer code for a coded ignition key or transponder fault. The immobilizer module could not read or validate the key's transponder code. Exact definitions vary by manufacturer.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Coded Ignition Key Malfunction
Code
B2790
Category
Body
Subsystem
Safety
Truck-relevant
Yes
What this means for truckers
Stop within ~50 miles on a Cummins X15, Detroit DD15, PACCAR MX-13. Driving longer risks damaging adjacent components (turbo housing, head gasket, aftertreatment) and turning a $300 fix into a $3,000 fix.
Before you replace parts — try this first
B2790 is an airbag (SRS) circuit code, most often damaged key transponder, or a key that is not programmed to the truck. Airbag circuits are not treated like ordinary sensors:
- Treat the airbag as possibly disabled. With an SRS code set, the airbag may not deploy in a crash. Get it diagnosed soon.
- Disconnect the battery and wait before touching anything. Follow the service manual wait time (often 1–10 minutes) so the SRS module reserve power drains.
- Never probe a squib circuit with a test light or ohmmeter. Use the manufacturer's SRS simulator/load tool and a scan tool that reads SRS codes.
- Check the cheap items first. Seat and clockspring connectors under the seat or behind the wheel are common causes after seat or steering work.
- Replace parts only after diagnosis. Some modules must be replaced, not reset, after a deployment.
Symptoms
No start, or start-and-stall, with the security light on or flashing. It may affect only one key or happen intermittently.
Common causes
- CommonDamaged key transponder, or a key that is not programmed to the truck ($60–$250)
- OccasionalFaulty immobilizer antenna or module at the ignition ($150–$500)
- OccasionalInterference from other keys or fobs on the ring ($0–$50)
- RareWiring or communication fault to the immobilizer module ($100–$350)
How to fix
Try a known-good programmed spare key with nothing else on the ring
When to use: First check
Program a new key with an OEM-level tool and security access
When to use: When only one key fails
Check the immobilizer module power, ground and data bus, and replace the module if needed
When to use: When all keys fail
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
Frequently Asked Questions
Can I drive with code B2790?
Drive with caution. B2790 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix B2790 on a commercial truck?
Total repair cost ranges varies depending on the root cause. The cheapest fix is usually the first one listed below — Damaged key transponder, or a key that is not programmed to the truck — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will B2790 fail a DOT inspection?
B2790 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between B2790 and related codes?
There are no directly related codes in the standard catalog. Diagnose this code on its own merits and check for any companion codes the ECM may have stored alongside it.
How do I prevent B2790 from coming back after a repair?
For B2790 (Coded Ignition Key Malfunction), prevention centers on the safety system. Don't disconnect the battery without the key off and a 5-minute wait — capacitors can hold airbag-deployment charge. Don't jumper or test airbag circuits with a multimeter (use OEM scan tool). Replace seat belts and connectors that have been involved in a deployment.