Intake Air Temperature (IAT) Circuit Low Input
This code indicates that the PCM has detected a low voltage reading that is out of the normal range for the intake air temperature sensor circuit.
Code Set Parameters
The PCM has detected a change in the IAT sensor signal circuit that is greater than acceptable or a change which has occurred in a time period that is shorter than acceptable. In applications which utilize multiple intake air temperature sensors, any voltage or readings that exceed a predetermined number of degrees (in variation of one another), will cause a code to be stored in the PCM and a service engine soon lamp may be illuminated. Some models will require multiple failure cycles in order for a malfunction indicator lamp to be illuminated; others will actuate service engine soon lamp illumination on the initial failure.
Symptoms can range from none at all to reduced fuel efficiency and either a lean or rich condition at cold startup. A code will be stored in the PCM and service engine soon lamp illumination may also accompany these symptoms.
The most common cause of this code is an IAT sensor that has been left unplugged after replacing the air filter. Other possible causes are a faulty IAT sensor (usually near the air filter housing), faulty electrical wiring or connectors, a faulty PCM.
IAT sensor failure is rare and most problems can be contributed to a disconnected electrical connector.
- The engine is equipped with an intake air temperature sensor (usually a two or three-wire variable resistance sensor) which provides the PCM with data
- Some vehicles are equipped with multiple intake air temperature sensors
- The primary intake air temperature sensor is usually located in the intake air inlet pipe, which is between the air filter housing and the throttle body
- The secondary intake air temperature sensor is typically located in a high flow area of the intake manifold
- Temperature readings are input to the PCM where they are compared
- If the PCM detects conflicting readings between the two sensors, a code will be stored and a malfunction indicator lamp may be illuminated
The sensor/s has a voltage wire (typically it is a 5-volt reference signal) and a ground wire
- The PCM uses the reference voltage wire to monitor intake air temperature
- As intake air temperature increases (along with ambient and engine temperature), sensor resistance decreases and reference voltage increases
- When the intake air temperature is cool, sensor resistance is high, driving reference voltage to the PCM down
- The PCM receives input reference voltage readings as variations in intake air temperature and reacts accordingly
- If variations in intake air temperature are excessive (or differ greatly from manufacturer’s specifications) a code is stored and a service engine soon lamp may be illuminated.
A scanner or code reader, a digital volt ohmmeter, and access to a manufacturer’s wiring schematic will be necessary to successfully diagnose this code
Begin your diagnosis with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- After the codes are cleared, operate the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made.
Continue by unplugging the electrical connector from the intake air temperature sensor and testing for reference voltage
- This is usually 5-volts but consult your manufacturer’s service manual to be sure
- If there is a 5-volt signal present with the ignition turned to the run position, check the sensor ground wire
- If both the reference signal and the ground signal are present, test the sensor resistance using the manufacturer’s temperature to resistance chart
- Compare your findings to the manufacturer’s specifications and replace the sensor if it fails to comply
- Clear the codes and test drive the vehicle to ensure that the repair is successful
If the sensor and voltage at the sensor are within acceptable specifications, disconnect the PCM electrical connector and test circuit continuity and resistance between the sensor and the PCM
- Repair or replace system circuitry and components as required
- Clear the codes and test drive the vehicle to ensure that the repair has been completed successfully.
Should all system circuitry and sensors check out, suspect a faulty PCM but keep in mind that PCM failure is rare and PCM replacement will require reprogramming.