Code
P1263
FORD
P — Powertrain
Cylinder #3 High To Low Side Short
Views:
UK: 24
EN: 62
RU: 47
AI status
Completed
Completed
100%
Causes
- Internal short in injector or ignition coil (depending on vehicle application)
- Damaged or chafed wiring harness creating contact between power and ground
- Corroded or pushed-back connector pins allowing shorting
- Shorted driver transistor inside the powertrain control module (PCM)
- Aftermarket components or incorrect replacement parts with incorrect impedance
- Water ingress or contamination at connector
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Rough idle or vibration, especially at idle or partial load
- Reduced engine power and drivability issues
- Cylinder 3 misfire (possible P0303 stored in addition)
- Blown fuse or repeated electrical faults affecting related circuits
- Possible fuel trim or emissions abnormalities
What to check
- Read all stored codes and freeze frame data; note any related codes (P0203, P0303, P0353, etc.)
- Check live data for misfire counts and injector/coil activity on cylinder 3
- Visually inspect wiring harness and connector for chafing, heat damage, corrosion, or water
- Check fuse(s) and wiring for the circuit; look for signs of shorted fuse(s)
- Measure injector or coil resistance at the connector and compare to spec
- Perform an on-vehicle wiggle test while monitoring for code set or voltage/current anomalies
Signal parameters
- Key ON engine OFF: supply rail voltage ~ battery voltage (12–14 V) at the injector/coil high side
- Driver/low side when active: pulses to ground under PCM control; expect switching waveform on oscilloscope
- Injector resistance (typical): ~1–16 ohms for low-impedance injectors or 11–16 ohms for high-impedance — consult vehicle spec
- Ignition coil primary DC resistance: manufacturer spec (often a few ohms); secondary measured per spec
- No continuous direct short to ground or supply when circuit inactive (infinite or very high resistance)
Diagnostic algorithm
- Record all codes and freeze frame. Note whether the code is current or history.
- Visually inspect connector, wiring, and harness routing for cylinder #3. Repair any obvious damage before further testing.
- Clear codes and attempt to re-create the fault. Monitor for immediate reset/return.
- Measure DC resistance of the injector (or coil primary) at the component and at the harness connector; compare to spec.
- With connector connected, back-probe the high-side (battery) and low-side (driver) terminals with a DVOM and/or oscilloscope to observe voltage and switching. Look for direct short or abnormal current draw.
- Perform a swap test: swap the injector or coil from cylinder 3 with another cylinder. If the code follows the part, replace the faulty part.
- If the fault remains on cylinder 3 after swapping, inspect and repair harness between the component and PCM (check continuity and short to ground/power).
- If wiring and component test good, suspect PCM driver fault. Verify PCM power/ground connections and consult manufacturer procedures for PCM testing or replacement.
- After repairs, clear codes and perform a road/in-use test to confirm fault does not return and that misfire or drivability is resolved.
Likely causes
- Faulty cylinder #3 fuel injector with internal short
- Faulty ignition coil or coil pack on cylinder #3 with internal short
- Pinched/damaged wiring between the injector/coil and PCM causing high-to-low short
- Corroded connector at the injector/coil causing unintended continuity
- PCM driver failure on cylinder #3 output
Fault status
Status
Cylinder #3 high-side to low-side short detected — electrical short between supply and driver for cylinder 3 circuit.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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