P0273
Cylinder 5 Injector Circuit Low
The appearance of the standard OBD2 trouble fault code P0273 is an indicator that your vehicle ECU triggered a threshold alert for "Cylinder 5 Injector Circuit Low". Understanding the root component breakdown helps avoid expensive diagnostic fees.
Driver's Summary
When your OBD2 scanner shows P0273, the engine control module has flagged an issue specifically related to cylinder 5 injector circuit low. In practice, this fault causes rough idle, severe hesitation, check engine light. This is not a code to ignore — the underlying fault can rapidly worsen and lead to costly repairs if driving continues.
Symptoms
Rough idle, severe hesitation, check engine light
Common Causes
- Short to ground in Cyl 5 injector wiring
- Failed injector coil internally
- Corroded plug
- Bad PCM
How to Fix
- 1 Repair grounded wiring
- 2 Replace Cyl 5 injector
- 3 Clean connector pins
- 4 Test PCM output
Technical Explanation
The ECM detects code P0273 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 fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
An active P0273 code under high-severity conditions means the affected system is operating outside safe parameters. Continued driving — especially under load or at highway speeds — significantly increases the risk of secondary damage to components like failed injector coil internally.
Mechanic's Pro Tip
Before replacing any component on P0273, 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