Broken or chafed wire in the injector harness between the PCM and cylinder 5 injector; Corroded or loose connector pins at the cylinder 5 injector or at the PCM; Failed cylinder 5 fuel injector with an open internal coil; Rodent damage to the injector wiring loom on top of the engine; Water intrusion into the injector connector causing corrosion and an open circuit; PCM driver circuit failure for cylinder 5 (less common but possible)

DTC codes / Ford codes / P1275

P1275 · FordCylinder 5 High To Low Side Open

Q: What does code P1275 mean?

Cylinder 5 High To Low Side Open. P1275 on a Ford means the powertrain control module (PCM) has detected an open circuit between the high side and low side of the fuel injector circuit for cylinder 5. The PCM commands the injector on and monitors the current flow, and when it sees no current or an unexpected voltage drop it flags this code because the injector coil or its wiring is not completing the circuit.

P1275 on a Ford means the powertrain control module (PCM) has detected an open circuit between the high side and low side of the fuel injector circuit for cylinder 5. The PCM commands the injector on and monitors the current flow, and when it sees no current or an unexpected voltage drop it flags this code because the injector coil or its wiring is not completing the circuit.

SystemPowertrain

Code typeFord specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

Often no symptoms besides the warning light, especially if the open is intermittent
A noticeable misfire or rough idle that may feel like a shake at stoplights
Loss of power and sluggish acceleration under load
Poor fuel economy as the PCM adds fuel to compensate for the dead cylinder
A flashing check engine light if the misfire is severe enough to damage the catalytic converter
Possible rotten egg smell from the exhaust if unburned fuel reaches the converter

Common causes, most likely first

Broken or chafed wire in the injector harness between the PCM and cylinder 5 injector
Corroded or loose connector pins at the cylinder 5 injector or at the PCM
Failed cylinder 5 fuel injector with an open internal coil
Rodent damage to the injector wiring loom on top of the engine
Water intrusion into the injector connector causing corrosion and an open circuit
PCM driver circuit failure for cylinder 5 (less common but possible)

How to diagnose and fix it

Inspect the cylinder 5 injector connector and harness for chafing, corrosion, or rodent damage
Disconnect the injector and measure resistance across its two terminals; compare to a known-good injector
Check for battery voltage at the injector high-side wire with the key on and engine off
Perform a continuity test from the injector low-side wire back to the PCM connector to find the open
Wiggle-test the harness while watching injector resistance or a noid light to catch intermittent opens
Repair or replace the damaged section of harness and clear the code
If wiring and injector test good, test the PCM driver circuit or substitute a known-good PCM for diagnosis

Why cylinder 5 injector opens are often misdiagnosed

A P1275 can set intermittently from a harness that only opens when the engine moves under torque, so a static resistance test at idle may pass and send you chasing the wrong part.
The code does not always mean the injector itself is bad; chafed wiring near the intake or valve cover is a very common cause on older Ford engines.
Technicians sometimes replace the injector only to find the connector pin has backed out of the shell, which creates the same open circuit and sets the code again immediately.
A noid light test at the cylinder 5 connector proves the PCM is commanding the injector but does not prove the injector coil is good, so always pair it with a resistance check.
If the open is on the low-side driver inside the PCM, the injector will test fine and the harness will test fine, which is the trap that leads to unnecessary injector replacement.

Can I keep driving with P1275?

You can drive short distances to a repair shop, but avoid heavy acceleration and long trips because a dead cylinder dumps unburned fuel into the catalytic converter and can overheat it. If the check engine light is flashing, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.