P0261 indicates that the powertrain control module (PCM) has detected a lower-than-expected voltage in the fuel injector circuit for cylinder 1. This typically means the injector or its wiring is shorted to ground or has an internal fault, preventing proper fuel delivery.
The injector itself may have an internal short to ground or a broken winding, causing low circuit resistance and triggering the code.
Damaged, chafed, or corroded wiring between the PCM and injector, or a loose/poor connection at the injector or PCM, can cause low voltage in the circuit.
A short circuit in the wiring harness where the injector signal wire contacts ground, bypassing the injector and creating a low-resistance path.
The PCM’s internal injector driver circuit may fail, causing incorrect voltage output. This is uncommon and should only be considered after all other causes are ruled out.
While a faulty PCM *can* cause this code, it is extremely rare. The PCM’s injector driver circuit would need to fail, which is uncommon. Always rule out wiring, connectors, and the injector itself first.
Some technicians may default to replacing the PCM due to misdiagnosis or unfamiliarity with injector circuit testing. However, PCM failure is a last-resort cause and should never be the first assumption.
Driving with this code may cause poor performance, misfires, or potential catalytic converter damage due to unburned fuel. It’s best to diagnose and repair the issue promptly.
Disconnect the injector and PCM connectors, then use a multimeter to check for continuity between the injector signal wire and ground. If continuity exists, there is a short in the wiring that must be repaired.