What does it mean?
On a turbocharged or supercharged engine the charge air cooler temperature sensor measures the air after the intercooler, while the intake air temperature sensor measures air entering the induction system. After a long cold soak nothing is heating the charge, so both sensors should read almost the same and both should be close to ambient. The module makes that comparison for bank 1 at the first key on and stores this code when the difference exceeds the allowed window, which indicates that one of the two has drifted. During normal driving the values legitimately separate, so the test only runs under soak conditions.
Symptoms
- MIL on, most often set on a cold morning start
- Softer boost response, since the module derates to protect against detonation
- Duller throttle and poorer fuel economy
- Charge air temperature on a scan tool that does not track the other intake readings
- Occasional knock or pinging under load on gasoline engines
- Hesitation or smoke under load on diesels
Likely causes
- Charge air cooler temperature sensor drifted, or its tip fouled with oil and soot carried into the intake
- Intake air temperature sensor drifted or heat soaked because of where it is mounted
- High resistance in a sensor signal or ground circuit shifting one of the values
- Sensor loose or not sealed in its port so it does not sit in the true air stream
- Incorrect replacement sensor with a different resistance curve
- Oil accumulation in the intercooler from a failing crankcase ventilation system coating the sensor
- Corroded terminal at one of the module inputs
How to fix it
- Read both temperatures after the vehicle has stood overnight and compare them with a measured ambient temperature
- Confirm with an infrared thermometer at the intercooler outlet and the intake duct while everything is still cold
- Check each sensor resistance or signal voltage against its temperature curve at a known temperature
- Inspect the charge air cooler temperature sensor for an oil film or soot, and check the intercooler for oil accumulation
- Measure the ground and reference circuits for voltage drop and inspect the connectors for corrosion
- Deal with the source of intake oil, such as a failing crankcase ventilation system, before fitting a new sensor
- Replace the sensor that is proven faulty with the correct part, then repeat the cold soak comparison