B1256

Step 1: Visually inspect the ambient air temperature sensor (typically located behind front bumper or grille area) and its connector for physical damage, corrosion, water intrusion, or pin damage. Disconnect the sensor connector and inspect terminals for bent pins or corrosion.

Step 2: With sensor disconnected and ignition on, use a digital multimeter to measure voltage on the signal wire at the harness side connector. Reading should be approximately 5V reference voltage. If reading shows battery voltage (12-14V), trace wiring for short to power.

Step 3: Perform resistance test on the sensor itself by measuring across sensor terminals with multimeter. Compare readings to manufacturer specifications (typically 2k-10k ohms depending on temperature). An open circuit or very low resistance indicates sensor failure.

Step 4: Inspect wiring harness routing from sensor to BCM for areas where harness may contact sharp edges, moving components, or heat sources that could have damaged insulation. Pay special attention to areas near headlight assemblies and radiator support.

Step 5: If wiring and sensor test normal, check for voltage leakage at BCM connector pins using a multimeter with ignition off. Resistance between signal circuit and battery positive should be infinite (open circuit).

Step 6: After repairs, clear codes, perform drive cycle with multiple temperature changes, and verify ambient temperature reading matches actual conditions on scan tool live data to confirm proper operation.