Code
B1315
HUMMER
B — Body
Evaporator Inlet Temp Sensor Short Circuit
AI status
Completed
Completed
100%
Causes
- Shorted sensor element (internal thermistor failure)
- Damaged/shorted wiring harness between sensor and HVAC control/module
- Corroded or damaged sensor connector (water intrusion possible)
- Short to ground or battery on sensor circuit
- Faulty HVAC control module or input circuit (less common)
- Incorrect replacement sensor or connector miswired
Symptoms
- A/C compressor disabled or cycles abnormally
- Incorrect or unstable cabin temperature regulation
- HVAC system stuck in defrost or default mode
- HVAC warning message or DTC lamp illuminated
- Intermittent HVAC operation or loss of automatic climate control
- Possible blower or blend door behavior changes (dependent on vehicle logic)
What to check
- Read and record freeze frame and live data using a scan tool; observe evaporator inlet temp value and any rapid changes
- Visually inspect sensor and connector at evaporator inlet for corrosion, damage, or moisture
- Backprobe sensor connector and measure voltage signal with key on, engine off (or per service manual)
- Measure sensor resistance with connector disconnected and compare to expected thermistor characteristics
- Wiggle wiring harness while monitoring live data to reproduce the fault
- Check for continuity to ground and short to battery on the sensor circuit
Signal parameters
- Type: NTC thermistor (resistance decreases as temperature increases)
- Typical resistance at ~25°C: roughly 1 kΩ–10 kΩ (varies by design) — consult vehicle-specific spec
- Expected signal voltage to module (via divider): typically ~0.5–4.5 V across normal temperature range
- Short-to-ground condition: signal voltage near 0.0–0.3 V or sensor resistance very low (< a few ohms)
- Open/short-to-Vb condition: signal voltage near reference (≈4.8–5 V) or infinite/high resistance
- Sensor response: smooth, gradual change in resistance/voltage with ambient temperature changes
Diagnostic algorithm
- Connect a capable scan tool and read stored codes and live evaporator inlet temperature PID. Note abnormal values (e.g., implausible low temp or constant 0°C).
- Visually inspect the evaporator inlet sensor, harness, and connector for corrosion, water intrusion, broken wires, or pin damage. Repair or dry as needed.
- With ignition ON (engine off unless otherwise directed), backprobe the sensor connector and measure signal voltage relative to ground. Compare to expected range. A near-zero voltage suggests short to ground; near reference voltage suggests open or short to battery.
- Disconnect the sensor and measure its resistance across the thermistor terminals at ambient temperature. Compare to service specification or expected NTC curve. Very low resistance indicates internal short; infinite indicates open.
- Perform a wiggle/stress test on the wiring harness while monitoring live data to identify intermittent shorts or opens. Repair chafed wires or broken conductors.
- Check continuity from the sensor connector to the HVAC control/module connector; verify no short to ground or battery on the sensor circuit using an ohmmeter (with battery disconnected when performing continuity checks to avoid damage).
- If wiring and sensor look good but fault persists, inspect HVAC control module connector pins for corrosion or bent pins. If available, swap with a known-good module or perform module input circuit resistance checks per manufacturer service info.
- After repair or replacement (sensor or wiring), clear codes, verify proper live PID values, and perform a functional test of the A/C system. Confirm code does not return on test drive or after environmental exposure.
Likely causes
- Damaged wiring or chafed insulation causing a short to ground
- Corroded or water-damaged connector at the evaporator inlet sensor
- Failed (shorted) evaporator inlet temperature sensor
- Pinched connector or improper reassembly after service
- Rare: failed climate control module input driver
Fault status
Status
Evaporator inlet temperature sensor circuit short detected. Climate control module has set a fault and may disable compressor or limit HVAC functions until fault is cleared and the circuit is repaired.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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