DTC B1249 - Ambient Air Temperature Sensor Circuit Low Input
Plain-English meaning
The Engine Control Module (ECM) has detected a low voltage input from the Ambient Air Temperature (AAT) sensor circuit, indicating a possible short to ground, sensor failure, or wiring issue.
What to check first
Inspect the Ambient Air Temperature sensor and its connector for corrosion, damage, or loose connections.
What not to replace yet
Do not replace the ECM without confirming wiring and sensor integrity first.
Stop driving when
Safe to continue driving; no immediate hazard. Repair recommended to restore proper sensor function.
Related symptoms
Incorrect ambient temperature display on climate control HVAC system behaving erratically Possible minor idle fluctuations Check Engine Light illuminated
Owner steps
Visually inspect the sensor and wiring for obvious damage. Ensure the sensor connector is fully seated and free of corrosion. Report any HVAC or temperature display abnormalities to a technician.
Likely causes
Ambient Air Temperature sensor faulty or damaged (medium)
Short circuit to ground in sensor wiring (medium)
Open or damaged wiring harness or connector (medium)
Corroded or loose connector terminals (medium)
ECM input circuit fault (medium)
Shop steps
Retrieve and confirm DTC B1249 with scan tool. Perform visual inspection of sensor, wiring, and connectors. Use a digital voltmeter to perform circuit test procedure on sensor wiring. Check sensor resistance against manufacturer specifications. Repair or replace wiring or sensor as needed. Clear codes and verify repair by test drive and scan tool data.
Follow-up questions
Is the ambient air temperature reading abnormal or missing on the climate control display?
Are there any signs of water intrusion or corrosion at the sensor connector?
Has any recent work been done near the sensor wiring or ECM connectors?
Are there any other DTCs present related to temperature sensors or HVAC?
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