Code
B0188
HUMMER
B — Body
Sunload Sensor Circuit
Views:
UK: 4
EN: 7
RU: 6
AI status
Completed
Completed
100%
Causes
- Faulty sunload (solar) sensor
- Open or shorted wiring in sensor harness
- Corroded, loose or contaminated connector at sensor or HVAC module
- Water intrusion or physical damage to sensor
- Blown fuse or loss of reference/power/ground to sensor
- Faulty HVAC control module / body control module (rare)
Symptoms
- Automatic climate control runs incorrectly (over- or under-compensates for sun load)
- Cabin temperature varies unexpectedly when sun exposure changes
- HVAC system defaults to a basic mode or displays a climate control fault
- DTC B0188 stored and may reappear after clearing
- Scan tool shows sunload sensor value stuck, zero, out-of-range or implausible
What to check
- Use a scan tool to read stored DTCs and live data for the sunload sensor (sensor value/voltage)
- Visual inspection: check sensor location on instrument panel/dash for contamination, shading, physical damage or water
- Inspect connector and pins for corrosion, bent pins, push/pull fit, moisture or debris
- With key ON (engine off as required), backprobe sensor connector to check reference voltage, signal voltage and ground
- Wiggle test harness while monitoring live data to look for intermittent faults
- Check related fuses and module grounds/power circuits
Signal parameters
- Typical reference supply: ~5 V reference (varies by vehicle); verify exact value from vehicle-specific manual
- Expected output: a variable voltage proportional to sunlight — commonly in a 0–5 V or ~0.5–4.5 V range under normal light conditions
- Short to ground: signal ≈ 0 V
- Short to battery/ref: signal ≈ reference voltage (e.g., ~5 V)
- Open circuit: signal may float to an extreme value or show no change with light
- Note: refer to vehicle-specific service data for exact voltage thresholds and units
Diagnostic algorithm
- Retrieve B0188 and any related codes with a scan tool and record freeze-frame and live sunload sensor data.
- Perform a visual inspection of the sunload sensor, mounting location, and harness for damage, contamination or shading sources.
- With ignition ON (per service manual), backprobe the sensor connector: verify reference voltage, ground continuity, and signal voltage. Compare to expected values from vehicle data.
- Lamp test: vary incident light on the sensor (cover/uncover or use a strong flashlight) while monitoring live signal to confirm the sensor output changes accordingly.
- Check for open/short: measure continuity between sensor connector pins and the HVAC/BCM connector pin to verify wiring integrity; repair any open/shorted wiring.
- Inspect and repair/clean corroded or loose connectors; reseal if water intrusion found.
- If wiring and connectors are good but the sensor output is incorrect or does not respond to light changes, replace the sunload sensor and clear codes.
- After repairs, clear codes and verify repair by cycling ignition, retesting sensor response and performing a test drive or environmental test to confirm the DTC does not return.
- If DTC returns and wiring/sensor verified, investigate HVAC/BCM input circuit or module fault per manufacturer procedures.
Likely causes
- Faulty sunload sensor
- Corroded/loose connector at the sensor
- Broken or shorted harness between sensor and HVAC/BCM
- Water intrusion in sensor area causing intermittent readings
- Loss of sensor reference voltage (fuse, wiring)
Fault status
Status
Stored when the HVAC/BCM detects an open, short, out-of-range or implausible signal from the sunload (solar) sensor circuit.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
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