P1278 Port Injector Circuit Number 3

Category: Powertrain - Fuel/Air Metering
Severity: Check Engine Light
Applies to: Toyota models with D-4S port injection

What does P1278 mean on a Toyota?

P1278. Port Injector Circuit Number 3. This Toyota-enhanced code applies to Toyota models with D-4S port injection.

Common causes of P1278

Open number 3 port injector circuit
Failed injector 3
Corroded connector
Harness fault
ECM driver fault

How to fix P1278

Test injector 3 resistance
Check pulse with a noid light
Verify wiring continuity
Inspect the connector
Replace the injector after circuit checks

Sources and review

Last updated 2026-09-06.