What this code means
P0072 may indicate the ECM is seeing the ambient air temperature signal as not plausible or outside the expected behavior for outside-air temperature information.
What the vehicle may do
- The vehicle may use a default ambient temperature value.
- A/C operation can be affected.
- The displayed outside temperature may update slowly or appear incorrect.
Possible fault areas
- Possible ambient air temperature sensor concern.
- Possible connector or terminal concern.
- Possible signal circuit or low-reference circuit concern.
- Possible ECM-side circuit concern.
Diagnostic path
Set the diagnostic frame
On this 2022 Chevrolet Silverado 2500 with the 6.6 diesel, P0072 is aimed at the ambient air temperature input. In plain language, the ECM may be seeing the outside-air temperature signal as not plausible. The truck may fall back on a default temperature value, A/C operation can be affected, and the possible fault areas are the ambient air temperature sensor, the connector, the signal and low-reference circuits, or the ECM side of the circuit. Start with the basic system checks before getting into the code path. When this fault is active, the air conditioning compressor clutch is disabled, and the control module uses default replacement values. If the scan tool has an ECM ambient air temperature calculation reset function, using it can help the displayed temperature update more quickly.
Confirm whether the code is current
Turn the ignition on with the vehicle in service mode. First, verify whether P0072 or the same ambient-temperature code family is setting. If it is set, go into circuit testing. If it is not set, check for any other ECM or temperature-related codes. If other codes are present, check what they mean first. If there are no other codes, let the vehicle completely cool to ambient temperature. Then compare the scan tool intake air temperature sensor parameter to actual ambient temperature. It should be within 15°C (27°F). If it is not, follow the intake air temperature sensor diagnosis before continuing. If it is within 15°C (27°F), compare the scan tool ECM ambient air temperature parameter to actual ambient temperature. That also should be within 15°C (27°F). If it is not, continue into circuit testing. If it is within range, this part of the path is OK, and the update can take up to 2 min.
Check the low-reference side first
For circuit testing, turn the ignition and all vehicle systems off, then disconnect the B9 ambient air temperature sensor connector. Test the low-reference circuit at terminal B, or terminal 2, to ground. You want less than 10 Ω. If the reading is 10 Ω or greater, disconnect the K20 engine control module connector and test that low-reference circuit from the component harness to the other end of the circuit. That test should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance in the circuit. If it is less than 2 Ω in that branch, the path calls for replacing the K20 engine control module. If the first low-reference test was less than 10 Ω, move on to the signal-side checks.
Check the signal response open and grounded
Turn the ignition on with the vehicle in service mode. With the ambient air temperature sensor disconnected, the scan tool ambient air temperature should read less than -34°C (-30°F). If it reads -34°C (-30°F) or warmer, turn the ignition off, disconnect the K20 engine control module connector, and test the signal circuit at terminal A, or terminal 1, at the component harness to ground. The expected result is infinite resistance. If the reading is less than infinite resistance, repair the short to ground on the circuit. If it is infinite resistance in that branch, the path calls for replacing the K20 engine control module. If the scan tool reading was -35°C (-31°F) or colder, continue with the jumper test.
Force the signal high and finish circuit checks
Connect a 3 A fused jumper wire between the signal circuit terminal A, or terminal 1, and the low-reference circuit terminal B, or terminal 2. Now the scan tool ambient air temperature should read greater than 143°C (290°F). If it reads 143°C (290°F) or colder, turn the ignition off and remove the jumper. Disconnect the K20 engine control module connector, turn the ignition back on in service mode, and test the signal circuit at the component harness to ground. It should be less than 1 V. If it is 1 V or greater, repair the short to voltage on the circuit. If it is less than 1 V, turn the ignition off and test the signal circuit from the component harness to the other end of the circuit. That should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance in the circuit. If it is less than 2 Ω in that branch, the path calls for replacing the K20 engine control module. If the jumper test produced 144°C (291°F) or warmer, the circuit response is OK and you can move back to the sensor and connector side.
Sensor check and repair verification
Apply dielectric grease to the connector terminals, then reconnect the B9 ambient air temperature sensor. Reproduce the operating conditions for the code and verify the repair corrected the DTC or symptom. If it did not, test or replace the B9 ambient air temperature sensor. For the sensor test, place the sensor in a stable, temperature-controlled area for at least 10 minutes. Then measure resistance between sensor signal terminal A, or terminal 1, and low-reference terminal B, or terminal 2. Compare that reading to the specified ambient air temperature sensor resistance. If the sensor is not in the specified range, replace the B9 ambient air temperature sensor. If it is in range, that check is OK. After any repair, verify the repair and confirm the code stays gone. The takeaway: prove the circuit response before condemning the sensor or the ECM. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0072 is often best approached by proving the ambient temperature circuit behavior first, then checking the sensor only after the circuit path makes sense.
For more guided automotive diagnostics, visit STEP Diagnostics.
