Yes. A P0118 code, which indicates an intake air temperature sensor circuit high input, can contribute to misfire-like symptoms by skewing the air-fuel mixture. However, this code is not a direct misfire fault; misfires are more commonly caused by ignition, fuel delivery, or compression problems. If the IAT reading is consistently too high or erratic, the engine management system may run lean or rich enough to cause rough running, hesitation, or occasional misfire under certain conditions.
What P0118 Means
P0118 stands for Intake Air Temperature Sensor Circuit High Input. It means the engine control module (ECM) is seeing a voltage or resistance that corresponds to an unusually high intake temperature reading in the IAT sensor circuit. A persistent high reading can cause the ECM to adjust fueling inappropriately, affecting performance and idle.
In modern vehicles, the IAT helps the ECM determine the density of incoming air so that the fuel injectors can meter the correct amount of fuel. If the sensor is faulty or its circuit is compromised, the resulting incorrect fuel trims can cause rough running, hesitation, and, in some cases, misfire.
Common causes of P0118 include:
- Faulty IAT sensor (stuck high, drift, or outright failure)
- Damaged or corroded wiring or connector in the IAT circuit
- Shorts to power or ground, or an open circuit in the IAT wiring
- Contamination or damage to the sensor element from oil, coolant, or dirt
- Engine or intake manifold leaking air in a way that the sensor readings are affected
If you see P0118, start with a thorough IAT sensor inspection and wiring check. Replacing a faulty sensor or repairing damaged harness typically resolves the code; however, the ECM’s fuel trims should be verified to ensure no residual misfueling remains.
Impact on Misfire: How It Manifests
P0118 can contribute to misfire-like symptoms because incorrect intake temperature readings lead to improper air-fuel ratios. In practice, you might notice hesitation during acceleration, rough idle, or reduced power, and in some cases, a misfire may occur in one or more cylinders if the fuel mixture becomes too lean for the engine under load or at idle. The presence of a misfire code (such as P0300 or P0301–P0308) is more definitive for a cylinder misfire, but P0118 can be a contributing factor.
It’s important to rule out ignition and fuel delivery faults as the primary cause of a misfire, since ignition coils, spark plugs, injectors, and pressure issues are common culprits. If the IAT system is confirmed faulty, replacing the sensor and repairing wiring often clears both the P0118 and associated running symptoms.
Diagnosing and Fixing P0118
To diagnose and fix P0118, follow a structured approach that verifies the sensor, harness, and related circuitry while ruling out other causes of misfire. The steps below provide a practical workflow.
- Use an OBD-II scanner to confirm P0118 and review freeze-frame data for the IAT reading vs ambient temperature.
- Inspect the IAT sensor and surrounding intake area for contamination, oil leaks, or damage. Clean or replace as needed.
- Check the IAT wiring harness and connector for corrosion, loose pins, breaks, or damaged insulation. Repair or replace as necessary.
- Test the IAT sensor resistance at various temperatures or compare with the service manual’s specifications to determine if the sensor is within expected range.
- Clear codes and perform a road test to see if P0118 reappears and whether engine performance improves or worsens.
- If the code persists after sensor and wiring checks, consider testing the PCM input with a professional scan tool or consulting a technician, as a faulty PCM or calibration can occasionally trigger anomalous readings.
Conclusion: Addressing the IAT circuit typically resolves P0118 and associated performance issues. If misfire symptoms persist after a repair, a comprehensive ignition and fuel system inspection should be conducted.
Summary
P0118 signals a high input on the intake air temperature sensor circuit and can affect engine fueling. While not a direct misfire code, it can contribute to rough running and hesitation that mimic misfires, especially if fuel trims are thrown off. The reliable fix is to inspect and replace the IAT sensor or repair wiring, and to verify there are no other underlying ignition, fuel, or compression problems.