Code
P1274
FORD
P — Powertrain
Cylinder #4 High To Low Side Open
AI status
Completed
Completed
100%
Causes
- Open or damaged wiring between PCM and cylinder #4 actuator (connector, broken conductor, chafing)
- Corroded, bent or poorly seated connector at the actuator
- Failed actuator/solenoid (injector, VCT/VVT or deactivation solenoid) on cylinder #4
- Poor or missing power supply (blown fuse, relay, or high-side circuit fault)
- Faulty PCM or driver circuit inside PCM
- Intermittent connection (water intrusion, heat-damaged insulation)
Symptoms
- MIL (Check Engine Light) set
- Cylinder-specific misfire (rough idle, hesitation, reduced power)
- Increased fuel consumption or poor drivability
- Stored misfire or injector/actuator diagnostic trouble codes for cylinder 4
- Possible intermittent operation of the related system (VVT, deactivation, etc.)
What to check
- Read and record freeze frame and related codes (misfire counts, fuel trims, other cylinder codes)
- Inspect connector and wiring at cylinder #4 actuator for damage, corrosion, or loose pins
- Backprobe connector and check for battery voltage on the high-side feed with key ON
- Command actuator on/off with a scan tool and monitor voltage at the low-side (should switch near 0V when grounded by PCM)
- Measure actuator coil resistance with connector disconnected and compare to service manual specification
- Perform continuity checks between actuator connector pins and the PCM connector
Signal parameters
- High-side supply (battery feed) — approx. battery voltage (~11–14.5 V with ignition ON/engine running)
- Low-side control (PCM switching) — should pull to ground (~0 V) when commanded ON; open/infinite when commanded OFF
- Actuator/solenoid coil resistance — see service manual; if unknown, expect a finite ohm value (not open/infinite)
- Live data: commanded state vs actual state (ON/OFF) should match when commanded via a scan tool
Diagnostic algorithm
- Connect a scan tool, read and record P1274 and any related codes (P0204, P0304, P1273, etc.) and freeze-frame data.
- Visually inspect wiring and connector at cylinder #4 actuator for damage, corrosion, broken retainers or water intrusion; repair as needed.
- With ignition ON, backprobe the actuator connector: verify high-side feed voltage is present and stable. If absent, trace fuse/relay and feed circuit.
- Command the actuator ON with a scan tool while measuring the low-side terminal. Low-side should switch close to 0 V when commanded. If it does not, suspect PCM driver or wiring open to PCM.
- With power removed, disconnect the actuator and measure coil resistance; compare to service manual. An open (infinite) reading indicates a failed actuator.
- Check continuity between the actuator low-side pin and the PCM low-side driver pin. Repair any open circuits. Also check for unintended shorts to battery or ground.
- If wiring and actuator test good, verify PCM grounds and power supplies. If all circuits test correctly and fault persists, consider PCM driver failure and consult OEM procedures for PCM testing/replacement.
- After repairs, clear codes and perform a road test and monitor live data to ensure the fault does not return and that cylinder operation is normal.
Likely causes
- Loose/corroded connector at the cylinder #4 actuator
- Open low-side return or high-side feed in harness (broken wire or pin)
- Failed actuator coil (open circuit)
- Damaged insulation causing an intermittent open when hot
- PCM driver fault (less common)
Fault status
Status
Manufacturer-specific fault: Cylinder #4 High-To-Low Side Open. Electrical open or improper signal between the high-side feed and low-side control for cylinder 4 actuator/solenoid detected by PCM.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
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