Code
B2147
HUMMER
B — Body
Left Front Mirror Horizontal Position Sensor Circuit High
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the left front mirror horizontal position sensor circuit
- Short to battery voltage on the sensor signal or supply
- Corroded or loose connector at the mirror or module
- Failed horizontal position sensor or potentiometer inside the mirror assembly
- Moisture/water intrusion in the mirror housing
- Faulty mirror control module or body control module (less common)
Symptoms
- Left exterior mirror horizontal position not adjusting or drifting
- Mirror position readout (if equipped) incorrect or pegged
- One or more mirror functions (fold/adjust) may be inoperative
- Illuminated body/mirror-related warning lamp or message
- Intermittent operation or codes returning after clearing
What to check
- Retrieve freeze frame and live data with a scan tool; observe mirror horizontal position sensor values while commanding mirror movement
- Visual inspection of left front mirror, harness, and connector for corrosion, damage, or water entry
- Wiggle test harness while monitoring live data to reproduce fault
- Backprobe sensor connector to check reference, signal, and ground voltages with key on and while operating mirror
- Check continuity and resistance of wiring between mirror connector and control module, and for short to battery or ground
- Inspect related fuses and grounding points
Signal parameters
- Reference (supply) voltage: typically ~5 V (varies by vehicle); check service manual
- Expected signal range: approximately 0.5–4.5 V during full sweep; mid position near ~2.5 V
- High fault threshold: signal above ~4.8–5.5 V or equal to battery voltage may set the code
- Resistance of a position potentiometer (if applicable): commonly a few kilo-ohms (check OEM spec)
- No signal/change when commanding mirror indicates open circuit or failed sensor
Diagnostic algorithm
- Read and record freeze frame and live data; clear codes and attempt to re-create the fault with the mirror commanded through its range.
- Visually inspect mirror housing, wiring, and connector for corrosion, water intrusion, pin damage, or rubbing/chafing.
- With key on (engine off), backprobe the mirror connector: verify reference voltage (5 V), sensor signal, and ground presence. Compare to expected values from vehicle manual.
- If signal is high (near battery voltage), isolate wiring: disconnect mirror assembly and re-check signal at harness side. If signal goes away, suspect mirror sensor or internal short to Vb in the mirror.
- If fault remains at harness side, check harness continuity to the control module and inspect for short to battery voltage using a DMM; repair any damaged wiring or connector faults.
- Perform wiggle testing of the harness and connectors while monitoring live data to find intermittent faults.
- If wiring and connectors are good and the mirror assembly is suspected, test or replace the mirror horizontal position sensor or the whole mirror assembly. Reconnect and verify operation.
- If a replacement mirror does not clear the code, inspect/replace the mirror control module or body control module only after confirming wiring and sensor are good. Consider reprogramming if required by manufacturer.
- After repairs, clear codes and confirm proper operation over several cycles and a road test if applicable.
Likely causes
- Corroded/loose connector at mirror (common)
- Open or shorted signal wire between mirror and module
- Failed mirror horizontal position sensor (potentiometer)
- Short to battery on signal or supply circuit
- Moisture damage inside mirror
Fault status
Status
Left Front Mirror Horizontal Position Sensor Circuit High
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Repair manuals
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138
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