P009A: Intake Air Temperature/Ambient Air Temperature Correlation

After a long standstill with the engine cold, intake air temperature and ambient air temperature should be about the same. P009A is set when the two sensors disagree by more than a threshold at the next start. A detected engine block heater usually suspends the test. Several manufacturers perform this comparison under other codes; no manufacturer description naming P009A itself was found. Suspects are both sensors, an ambient sensor in a heat-affected position and contact resistance at a connector.

Symptoms

• Check engine light on
• Usually no noticeable symptoms

Most likely causes

• Intake air temperature sensor drifting or contaminated
• Ambient temperature sensor faulty or in a heat-affected position
• Contact resistance at a connector
• Engine block heater or auxiliary heater distorting the comparison

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, compare the reading with the outside temperature
2. Compare both signals at the same time in live data and check any recent installation work.
3. Check the connector
4. Measure the sensor's resistance against the manufacturer's specification
5. Check power and ground before replacing it

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P009A means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 0: Subsystem depends on the code range
• 9A: Specific fault in that system

Frequently asked questions

Can I keep driving with code P009A?

Yes, you can normally keep driving and take it to a repair shop when convenient.

What causes code P009A?

The most common causes are: intake air temperature sensor drifting or contaminated; ambient temperature sensor faulty or in a heat-affected position; contact resistance at a connector.

Related codes

• P0071Ambient Air Temperature Sensor Circuit A Range/Performance
• P0111Intake Air Temperature Sensor 1 Circuit Range/Performance Bank 1
• P00CEIntake Air Temperature Measurement System - Multiple Sensor Correlation Bank 1
• P0070Ambient Air Temperature Sensor Circuit A

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 10241746 9999
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.