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DTC codes / Ford codes / P1273

P1273 · FordCylinder 3 High To Low Side Open

P1273 on a Ford vehicle means the powertrain control module has detected an open circuit between the high side and low side of the fuel injector circuit for cylinder 3. The computer commands the injector on and monitors the electrical response, and it sees no current flow or an unexpected voltage pattern that indicates a break in the circuit.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Illuminated check engine light, often with no other symptoms besides the warning light
  • Rough idle or misfire that is most noticeable when the engine is cold or under light load
  • Noticeable loss of power and reduced fuel economy because cylinder 3 is not contributing
  • Shaking or vibration from the engine bay that worsens during acceleration
  • A faint fuel odor from the exhaust if the injector is stuck open or the circuit is intermittent
  • In some cases the engine may enter limp mode and limit RPM to protect the catalytic converter

Common causes, most likely first

  1. Broken or chafed wire in the cylinder 3 injector harness, often near the valve cover or where the harness bends
  2. Corroded or loose electrical connector at the cylinder 3 fuel injector
  3. Failed fuel injector with an open internal coil winding
  4. Damaged pin or terminal in the injector connector or at the powertrain control module connector
  5. Rodent damage to the injector wiring loom, which is common on Ford vehicles parked outdoors
  6. A short to ground or short to voltage in the injector control circuit that mimics an open circuit

How to diagnose and fix it

  1. Inspect the cylinder 3 injector connector and harness for corrosion, chafing, or loose pins, and repair any damaged terminals
  2. Measure the resistance of the cylinder 3 injector with a multimeter and compare it to the specification for your engine
  3. Check for continuity and short-to-ground on both the high and low sides of the injector circuit from the injector connector to the powertrain control module
  4. Perform a wiggle test on the harness while watching injector data or listening for a change in engine idle to catch intermittent opens
  5. Swap the cylinder 3 injector with a known-good injector from another cylinder and see if the code moves to confirm the injector is at fault
  6. If the circuit and injector test good, check the powertrain control module connector pins and driver circuit for damage or corrosion
  7. Clear the code and perform a road test with live misfire data to verify the repair before returning the vehicle

What Ford injector circuits hide from scanners

  • A P1273 can set without any driveability complaint because the injector circuit may only open intermittently when the engine bay is hot or the harness flexes over bumps.
  • Technicians often replace the cylinder 3 injector first, but chafed wiring near the valve cover or a corroded connector pin is a more frequent cause on high-mileage Ford engines.
  • The code does not always mean the injector itself has failed; a shorted or open driver inside the powertrain control module can produce the same high-to-low side open reading.
  • Rodent damage to the injector harness is common on Ford vehicles that sit outside, so inspect the loom carefully before condemning any electrical component.
  • A misfire counter that stays at zero does not rule out this code, because the fault may be stored from a single key cycle when the circuit briefly opened.

Can I keep driving with P1273?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration and long trips because raw fuel from a dead cylinder can overheat and damage the catalytic converter. If the engine is shaking badly or the check engine light is flashing, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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