DTC code
B2278
Engine Switch Circuit Malfunction (Toyota/Lexus)
Technical guide
Symptoms
- Difficulty starting the engine
- engine failing to switch off properly
- intermittent stalling reported.
Probable causes
1) Faulty engine (power/ignition) switch — mismatched SSW1/SSW2 contact signals. 2) Damaged wiring or connectors in the engine switch circuit. 3) Malfunctioning control module (ECM / smart key ECU).
Diagnostic steps
- Confirm the vehicle make and system — B2278 meaning differs per manufacturer; on Toyota/Lexus it applies to the smart key push-button start system.
- Retrieve codes with a scan tool and note freeze frame conditions.
- Check engine switch operation: verify that the SSW1 and SSW2 contact signals match when the switch is pressed, per the factory diagnostic procedure.
- Inspect the wiring and connectors of the engine switch circuit for damage, corrosion or loose pins.
- Replace the engine switch if the contact signals do not match with good wiring.
- If switch and circuit test good, diagnose the control module per the factory manual.
- Clear codes and verify normal start/stop operation.
Cross-checked technical synthesis (QA). It does not replace the manufacturer's procedure.
Models most reported with this code (NHTSA)
Count of distinct owner complaints mentioning the code. US data — same engines, same failures.
AI here is a librarian: this page shows only what mechanics confirmed, or says “unknown”. It never suggests a diagnosis — MECCANIC interprets the code, never your car.
0 confirmed cases on B2278
Nothing confirmed yet for this code. No guess is offered on purpose.
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