P0271
Cylinder 4 Injector Circuit High
If your code reader dashboard displays the generic DTC error code P0271, your vehicle is currently experiencing an active failure related to "Cylinder 4 Injector Circuit High". Proper system troubleshooting is required to safely clear this warning.
Driver's Summary
Your vehicle's computer logged P0271 after detecting a malfunction in the cylinder 4 injector circuit high system. In practice, this fault causes misfire, rich condition, poor fuel economy. This is a serious fault — avoid extended driving and have your vehicle inspected by a mechanic as soon as possible to prevent further damage.
Symptoms
Misfire, rich condition, poor fuel economy
Common Causes
- Short to battery in Cylinder 4 circuit
- Faulty fuel injector
- Wiring harness damage
- Internal PCM failure
How to Fix
- 1 Trace short to power and repair
- 2 Replace fuel injector
- 3 Repair and wrap wiring harness
- 4 Test PCM
Technical Explanation
The ECM detects code P0271 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The PCM monitors crankshaft rotational velocity via the CKP sensor at a resolution of individual tooth gaps on the reluctor ring. A combustion event in each cylinder produces a measurable acceleration spike; its absence or weakness is flagged as a misfire event within a 200-revolution or 1000-revolution test window. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
This fault carries real mechanical risk. The root causes — including short to battery in cylinder 4 circuit — can trigger a chain reaction of component failures if the vehicle continues to be driven. Have it towed or drive directly to a shop without delay.
Mechanic's Pro Tip
Before replacing any component on P0271, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
Injector: $200 - $450; Wiring repair: $100