Technical Description of OBD-II Trouble Code
Intake Air Temperature Exceeds Recommended Level
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (Dodge, Chrysler, Hyundai, Jeep, Mazda, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
A stored code P0127 indicates that the powertrain control module (PCM) has detected an input signal from the intake air temperature (IAT) sensor circuit, which indicates that the temperature or circuit voltage is too high.
The PCM uses the input signals from the IAT sensor and the mass airflow (MAF) sensor to calculate fuel delivery and ignition timing. Maintaining an air/fuel ratio of 14.7:1 is crucial for engine performance and fuel efficiency, making the input from the IAT sensor critical.
The IAT sensor is usually located in the air inlet pipe or air cleaner box, but it may also be threaded directly into the intake manifold. In some cases, the IAT sensor may be integrated into the MAF sensor housing. Regardless of its design, it must be positioned in a way that allows ambient air, drawn into the intake manifold through the throttle body, to continuously and consistently flow across it while the engine is running.
The IAT sensor is typically a two-wire thermistor sensor. As the air flow varies across the cold wire element, the sensor resistance changes according to the temperature. In other words, the more air that flows across the cold-wire element, the lower the temperature and resistance it provides. OBD II equipped vehicles usually use a reference voltage (typically five volts) and a ground signal, with the IAT sensor completing the circuit. The varying resistance in the IAT sensor element causes voltage fluctuations in the input circuit. The PCM recognizes these fluctuations as variations in intake air temperature.
If the PCM detects a voltage level from the IAT sensor that exceeds the maximum allowable limit, it will store a code P0127 and may illuminate the malfunction indicator lamp (MIL).
Severity & Symptoms
The IAT sensor signal is used by the PCM to determine the fuel delivery strategy, so a code P0127 should be considered severe. Symptoms of a P0127 code may include:
Causes
Possible causes for this code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
When diagnosing a code P0127, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer, and a reliable source of vehicle information (such as All Data DIY).
I would begin by connecting the scanner to the vehicle’s diagnostic connector and retrieving the stored trouble codes and applicable freeze frame data. I recommend writing down this information in case it is needed later. Next, I would clear the codes and test-drive the vehicle. If the code is reset, proceed to the next step.
I would then visually inspect the IAT sensor-related wiring and connectors (including the air filter and air inlet pipe). Pay close attention to the sensor connector, as it is prone to corrosion due to its proximity to the battery and coolant reservoir. Check for any relevant technical service bulletins (TSB) that apply to the vehicle and the specific malfunction.
If the system wiring, connectors, and components appear to be in good working order, I would continue by connecting the scanner to the diagnostic connector and accessing the data stream. To obtain a faster response, narrow down the data stream to include only relevant data. Using an infrared thermometer, verify that the IAT reading on the scanner accurately reflects the actual intake air temperature.
If the temperatures coincide, consult your vehicle information source for IAT sensor testing recommendations. Use the DVOM to test the sensor and compare the results with the manufacturer’s specifications. If the sensor fails to meet the specifications, it must be replaced.
If the resistance test of the sensor passes, check for sensor reference voltage and ground at the sensor connector. If reference voltage and grounds are not present, repair the open or shorted circuit and retest the system. If the system reference and ground signals are present, refer to the IAT sensor voltage to temperature chart in your vehicle information source and use the DVOM to test the sensor’s output voltage. Compare the actual voltage with the temperature to voltage chart. If the actual reading deviates from the chart, replace the sensor.
If the IAT reference voltage is within specifications, disconnect the electrical connectors from all related controllers and use the DVOM to test the resistance and continuity in all system circuits. Repair or replace any circuits that are found to be open or shorted.
Additional diagnostic notes:
Related IAT sensor and circuit trouble codes: P0095, P0096, P0097, P0098, P0099, P0110, P0111, P0112, P0113, P0114
