What it means
The intake air temperature and ambient air temperature readings do not correlate as expected.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The intake-air and ambient-air temperature sensors measure temperatures at different points, and the control module checks whether their readings make sense together under the current conditions. P009A sets when the two readings do not correlate as expected, which can result from either sensor being inaccurate or from a fault in either sensor's wiring.
Common causes
Most likely first.
- Intake air temperature sensor reading inaccurate
- Ambient air temperature sensor reading inaccurate
- Wiring or connector fault affecting either sensor
Symptoms
- Check engine light on
- Poor fuel economy
- Rough idle or hesitation
How to diagnose it
- Review freeze-frame data and compare live intake-air and ambient-air readings to identify which reading appears implausible for the conditions.
- After the vehicle has sat long enough to cool, compare both readings with the surrounding air temperature before the engine warms up.
- Inspect the intake-temperature and ambient-temperature sensor connectors and wiring for loose plugs, corrosion, or damage.
- Check each sensor's live-data response as conditions change, using the wiring diagram to distinguish a sensor problem from a circuit fault.
- Test the suspect sensor circuits and compare their readings with the manufacturer's specification before replacing either sensor.
Common fixes
- Reconnect a loose intake-air or ambient-air sensor connector.
- Repair damaged or corroded wiring to the sensor whose reading is implausible.
- Replace the intake-air temperature sensor if its reading fails verification.
- Replace the ambient-air temperature sensor if it is the inaccurate reading.
Can I keep driving?
If the engine runs normally, driving is generally possible, though incorrect temperature data can affect fuel economy or cause hesitation. Limit driving if rough running or hesitation makes the vehicle difficult to control.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.