Code
P1532
HUMMER
P — Powertrain
A/C Evaporator Temp. Sens. Circuit Low Voltage
Views:
UK: 8
EN: 14
RU: 11
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in evaporator temp sensor circuit (short to ground)
- Bad or corroded connector at the evaporator temperature sensor
- Failed evaporator temperature sensor (thermistor)
- Faulty HVAC control module / body control module / ECM input
- Water intrusion or mechanical damage in the evaporator area causing sensor failure
- Intermittent connector contact or bent terminals
Symptoms
- A/C compressor cycling abnormally or stuck on/off (frost protection active)
- Erratic cabin temperature control or inability to maintain set temperature
- Reduced A/C cooling performance
- Ice formation on evaporator if sensor reading too warm/too cold incorrectly
- DTC stored; possible HVAC system limp/limited operation
What to check
- Scan tool: read evaporator temp PID and confirm low voltage or unexpectedly low temperature reading
- Visually inspect evaporator sensor connector and wiring for corrosion, damage, or water ingress
- Backprobe sensor connector and measure signal voltage with key ON and A/C enabled
- Measure sensor resistance at sensor unplugged across sensor terminals and compare to expected temp vs resistance behavior (thermistor)
- Check continuity from sensor connector to HVAC/module connector and for shorts to ground or power
- Perform wiggle test on harness while monitoring signal/PID for intermittent faults
Signal parameters
- Typical thermistor-type sensor: signal range approx. 0.5–4.5 V (varies by vehicle). Low voltage = below expected range for ambient temperature.
- Approx. behavior: colder temperatures → lower or higher voltage depending on sensor type (confirm with service data).
- Expected room-temperature signal often near mid-scale (~2–3 V) — verify in factory data.
- Typical thermistor resistance varies with temperature (NTC examples: several kΩ at 25 °C); compare measured resistance to service specifications.
Diagnostic algorithm
- Read and record freeze frame data and PID value for evaporator temp with a scan tool.
- Visually inspect sensor connector and wiring at the evaporator for damage or corrosion; repair any issues.
- Backprobe sensor connector: with ignition ON and A/C request active, measure reference voltage, signal voltage and ground. Typical checks: - Verify sensor has proper reference/pull‑up and ground. - If signal is low, check for short to ground in the signal circuit.
- If wiring appears intact, unplug sensor and measure sensor resistance at ambient temperature. Compare to specification or observe expected resistance change when applying cold (ice) or warm (hand) to sensor.
- If sensor resistance and response are within spec but signal remains low at module, verify continuity from sensor connector to HVAC/ECM input and check for short to ground/power.
- If wiring and sensor check good, verify module input operation or replace sensor and retest. Clear codes and perform functional test; confirm code does not return.
- If module suspected, consult service manual for module test procedures before replacement.
- Document repairs and perform a final scan to confirm proper PID behavior and that DTC does not return.
Likely causes
- Corroded/loose connector behind dash near evaporator case
- Wire chafing to ground in harness routed through bulkhead or HVAC plenum
- Thermistor element shorted internally (sensor failure)
- Aftermarket work or prior repair disturbed harness/connector
- HVAC module providing incorrect reference/pull‑up voltage (less common)
Fault status
Status
A/C evaporator temperature sensor circuit — low voltage detected. Inspect sensor and wiring.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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