Code
B1278
ALFA ROMEO
B — Body
Footwell servo potentiometer short to positive
Views:
UK: 6
EN: 6
RU: 5
AI status
Completed
Completed
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Causes
- Damaged/shorted potentiometer inside footwell servo (actuator)
- Chafed/damaged wiring harness with insulation rubbed through, contacting +12V
- Corroded/contaminated connector causing a high-voltage path
- Aftermarket accessories or recent repair that spliced into the circuit incorrectly
- Faulty body control / climate control module reporting erroneous fault
Symptoms
- HVAC footwell flap stuck in one position or not moving
- Incorrect or erratic footwell airflow or temperature control
- HVAC control display may show actuator or position feedback fault
- Possible stored climate control DTCs, no engine MIL
What to check
- Visual inspection of footwell servo connector and wiring for damage or contamination
- Backprobe the potentiometer signal wire with ignition ON and observe voltage
- Check for continuity between signal wire and battery + with ignition OFF (expect open)
- Resistance check of potentiometer pins (if serviceable)
- Inspect for recent work near wiring bundles that could have disturbed harness routing
Signal parameters
- Expected potentiometer output typically ~0.5–4.5 V (varies by model); full-scale roughly 0–5 V depending on ECU
- With ignition ON and actuator at one extreme expect voltage near end of range (model-specific)
- Potentiometer total resistance often 5 kΩ–20 kΩ (consult vehicle wiring diagram/service manual)
- Short-to-positive condition: signal wire measures battery voltage (~12 V) or near battery with respect to ground
Diagnostic algorithm
- Read and record all stored HVAC/body module DTCs and freeze frame data. Do not clear codes yet.
- Visually inspect the actuator, connector and wiring harness from the footwell actuator to the control module for chafing, pin damage, corrosion or evidence of a short to a fused +12V circuit.
- With ignition ON (accessory), backprobe the potentiometer signal wire at the actuator connector. Measure voltage to chassis ground. A short-to-positive fault will show ~battery voltage. If so, remove power before further testing.
- With ignition OFF, check continuity between the signal wire and battery + terminal. There should be high resistance/open. Direct continuity indicates a short.
- Disconnect the actuator and measure resistance between the potentiometer pins on the actuator (if serviceable). Compare to spec. If the internal potentiometer shows near-zero resistance to +12V supply terminal, it is faulty.
- If wiring appears intact at the actuator, trace wiring and disconnect intermediate connectors to isolate the short. Repair damaged wiring/replace connector as needed.
- After repairing wiring or replacing the actuator, clear codes and perform an actuator calibration/learn procedure per service manual. Re-scan and verify proper operation and that the DTC does not return.
- If wiring and actuator test good but fault persists, test/replace the climate control/body module or consult wiring diagrams for module driver tests. Consider professional diagnostic equipment for module-level checks.
Likely causes
- Wiring damage with conductor contacting fused +12V (most likely)
- Failed potentiometer in the footwell servo
- Corroded connector at actuator
- Less likely: internal module driver failure
Fault status
Status
Footwell servo potentiometer signal circuit detected short to battery positive (high voltage on position feedback).
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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