Code
B1311
HUMMER
B — Body
Outside Air Temp Sensor Short Circuit
AI status
Completed
Completed
100%
Causes
- Damaged OAT sensor (thermistor) with internal short
- Wiring shorted to battery positive or ground (chafed, pinched, damaged insulation)
- Corroded or damaged connector terminals
- Faulty module input (BCM/HVAC/cluster) or internal short in harness
- Poor ground or power supply to sensor circuit
- Moisture intrusion at sensor or connector
Symptoms
- Ambient/outside temperature display incorrect (fixed value or extreme)
- HVAC automatic mode may behave improperly (wrong blending/fan behavior)
- Possible stored DTC and warning/message in instrument cluster
- Climate control may prevent proper recirculation logic or A/C behavior
What to check
- Retrieve DTCs and freeze‑frame data with a scan tool; note live OAT reading
- Visually inspect sensor and wiring from sensor to module for damage and corrosion
- Backprobe connector and monitor sensor voltage or resistance at key temperatures
- Compare displayed ambient temperature to a handheld thermometer placed near sensor
- Perform continuity checks for short to ground and short to battery (+) on the sensor circuit
- Wiggle-test harness while watching live data to see intermittent changes
Signal parameters
- Typical sensor type: NTC thermistor (resistance decreases as temperature rises)
- Expected signal: varies with ambient temperature; typical module input voltage range ≈ 0.1–4.9 V (manufacturer dependent)
- Typical resistance range (manufacturer dependent) can span from a few kΩ at warm temps to tens/hundreds of kΩ at cold temps
- Short symptoms: near 0 Ω or near battery voltage on signal line, or fixed out‑of‑range voltage
- Open symptoms: very high resistance / infinite Ω or signal floating to an open‑circuit default voltage
Diagnostic algorithm
- Verify code: clear codes and attempt to re-create or monitor live data to confirm B1311 returns.
- Record ambient reading from scan tool and compare to a handheld thermometer placed at the OAT sensor location.
- Visually inspect sensor mounting area (usually front bumper/behind grille) for damage, debris, or moisture.
- Disconnect sensor connector, inspect terminals for corrosion, pushed pins, or melted plastic.
- With ignition ON, measure voltage at the sensor connector between signal and ground; note if voltage is near battery voltage or ground (indicates short).
- Measure resistance of the sensor removed from circuit across its terminals; compare to manufacturer spec or verify it changes when placed in ice water and warm water (resistance should change smoothly).
- Check continuity between the signal wire and chassis ground and between the signal wire and battery positive to identify shorts; isolate harness sections as needed.
- If harness appears OK, check module input pin for proper operation (voltage supply and pull‑up/pull‑down behavior).
- Repair or replace damaged wiring, connector, or sensor. Protect harness routing and reseal connectors against moisture.
- After repair, clear codes and verify sensor reads correctly across normal operating temps and that code does not return.
Likely causes
- Connector or wiring insulation rubbed through and contacting body or harness
- Terminal pushed out of connector or bent, causing short
- Sensor element failed (internal short)
- Water penetration causing low resistance path
- Aftermarket equipment or recent service disturbed wiring
Fault status
Status
B1311 — Outside Air Temperature Sensor Short Circuit. The sensor circuit is reporting a short (to power or to ground) or a signal outside expected range. Inspect sensor, wiring, and connector for damage or corrosion; verify sensor resistance/voltage and repair as needed.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
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Repair manuals
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138
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