Code
B1268
ALFA ROMEO
B — Body
Defrost servo potentiometer circuit
AI status
Completed
Completed
100%
Causes
- Open or short in potentiometer signal, reference or ground circuit
- Corroded/damaged connector or wiring harness to the defrost servo
- Failed potentiometer inside the defrost servo (wear or contamination)
- Seized or mechanically damaged defrost servo causing pot damage
- Poor ground or intermittent connection at HVAC control module
- Faulty HVAC control module or software/firmware error
Symptoms
- Cannot select or hold defrost air distribution (air not directed to windshield)
- HVAC mode may stick, jump, or not move to commanded position
- HVAC control displays an error or shows incorrect flap position
- Intermittent or no response from defrost control even though blower runs
- Possible stored additional HVAC/body control fault codes
What to check
- Read and record all stored HVAC/body control module fault codes and freeze frame data
- Visually inspect defrost servo, connector, and wiring for damage, corrosion or pin push-out
- Operate HVAC mode selection while watching servo movement and connector for intermittent behavior
- Check for proper power and ground at the servo connector
- Measure potentiometer signal voltage at rest and while moving the mode lever (should vary smoothly)
- Perform continuity and resistance checks from HVAC module connector to servo connector
Signal parameters
- Reference voltage: typically +5 V (check vehicle spec)
- Potentiometer wiper signal: varies from ~0.5–4.5 V depending on position (should change smoothly with movement)
- Potentiometer total resistance: commonly in the 5 kΩ–20 kΩ range (vehicle-specific)
- Ground: near 0 V with low resistance to chassis ground
- No short to battery voltage or chassis ground on the signal wire when in any position
Diagnostic algorithm
- Retrieve freeze frame and related codes. Note any pattern (open/short/intermittent).
- Inspect connector and harness at defrost servo for corrosion, damage, or pin movement. Repair as needed.
- With ignition ON, backprobe the servo connector: verify reference voltage present, good ground, and measure wiper signal while changing mode. Confirm signal varies smoothly between end stops.
- If no reference or ground, trace and repair supply/ground circuits to HVAC control module. Check module-side connector and fuses.
- If reference and ground are good but signal is open/erratic, disconnect servo and measure resistance across pot terminals. Compare to specification and check for continuity.
- Repair any wiring faults found (splices, broken wires, corroded pins). After repair, clear codes and test HVAC operation repeatedly through full range.
- If wiring and potentiometer fail tests, replace the defrost servo (or entire actuator assembly) and retest. Verify code does not return.
- If fault persists after replacing servo and wiring, inspect/replace HVAC control module or perform module reprogramming as per manufacturer guidance.
Likely causes
- Broken wire at harness flex point or behind dash
- Corroded pins in the potentiometer connector
- Internal potentiometer wear (dirty track) causing intermittent readings
- Short to chassis ground or to battery voltage on the signal lead
- Defrost servo motor gear failure causing pot to be out of range
Fault status
Status
Defrost servo potentiometer circuit fault — electrical fault in potentiometer signal, reference, or ground. Inspect servo, connector, wiring, and HVAC control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Repair manuals
Manual library for ALFA ROMEO
89
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