P027C
Cylinder 1 Injector Circuit Range/PerformanceP027C is a generic OBD-II powertrain diagnostic trouble code: Cylinder 1 Injector Circuit Range/Performance. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P027C means
P027C indicates that the PCM/ECM has detected an electrical or functional anomaly in the fuel injector circuit for cylinder 1. The control module monitors injector driver current waveforms and compares them against expected parameters during normal operation. When the measured response falls outside the calibrated window, this code is stored and the MIL is illuminated.
Common causes include high-resistance connections at the injector harness connector, a partially failing injector solenoid, or a fault in the injector driver circuit within the PCM itself. Because injector timing and pulse width are tightly managed, even minor circuit degradation can affect fuel atomisation and combustion quality in cylinder 1.
The fault may be intermittent, appearing only under high fuel demand or temperature extremes. Technicians should inspect wiring and connector integrity before condemning the injector or PCM, as corrosion and chafed wiring are frequent root causes on high-mileage vehicles.
Common causes
Most-frequently reported root causes when P027C is logged.
-
1
High resistance or open circuit in the cylinder 1 injector wiring harness.
-
2
Corroded or backed-out pin at the injector electrical connector.
-
3
Faulty cylinder 1 fuel injector solenoid winding.
-
4
Short to ground or short to voltage in the injector signal wire.
-
5
Failed injector driver circuit inside the PCM/ECM.
-
6
Fuel delivery issue causing abnormal injector back-EMF signature.
-
7
Water intrusion into the injector connector causing intermittent resistance.
Symptoms drivers notice
How to diagnose P027C
A typical diagnostic flow when this code is present.
-
1
Connect a scan tool and record all stored DTCs and freeze frame data.
-
2
Inspect the cylinder 1 injector wiring harness for chafing, burns, or corrosion.
-
3
Check the injector electrical connector for backed-out pins and corrosion; clean or repair as needed.
-
4
Measure injector solenoid resistance and compare to manufacturer specification.
-
5
Using a lab scope, observe the injector driver waveform while cranking or idling to confirm circuit integrity.
-
6
Perform a cylinder contribution test with the scan tool to evaluate cylinder 1 power balance.
-
7
If wiring and connector are good and injector resistance is out of spec, replace the cylinder 1 injector.
Related powertrain codes
Frequently asked questions
Can I drive with P027C active?
Short trips are generally possible, but extended driving with a misfiring cylinder can damage the catalytic converter and should be avoided.
Is P027C always a bad injector?
No. Wiring faults and connector corrosion are equally common causes and should be ruled out before replacing the injector.
Will P027C cause a failed emissions test?
Yes. An active MIL will cause an automatic failure in most OBD-II emissions inspection programs.
Can a weak fuel pump trigger P027C?
Indirectly. Insufficient fuel pressure alters injector back-EMF, which the PCM may interpret as a circuit range fault.
Disabling P027C in software
RaceTune can permanently disable P027C — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P027C in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file