Code
C1091
ALFA ROMEO
C — Chassis
Right rear discharge valve
Views:
UK: 3
EN: 6
RU: 9
AI status
Completed
Completed
100%
Causes
- Open or shorted solenoid coil in the right rear discharge valve
- Corroded, loose, or damaged connector or wiring harness to the valve
- Poor ground or supply voltage to the ABS hydraulic unit
- Contamination or internal mechanical seizure of the valve
- Faulty ABS/ESP hydraulic control unit (modulator)
- Low brake fluid or air in hydraulic circuit affecting valve operation
Symptoms
- ABS warning light (and possibly traction control light) illuminated
- ABS or traction control functions reduced or disabled
- Changes in pedal feel during ABS activation or erratic ABS operation
- Brake performance affected under ABS activation (longer stopping distance)
- Possible diagnostic trouble codes for other ABS components or wheel sensors
What to check
- Read and record all stored ABS/ESP fault codes and freeze frame data with an appropriate scan tool
- Perform a visual inspection of the right rear discharge valve connector and wiring for damage, corrosion, or chafing
- Check brake fluid level and condition; inspect for contamination or leaks at the hydraulic unit
- Compare resistance of the right rear valve solenoid to the same valve on the opposite side (if identical) or to specification
- Verify battery voltage and ground at the valve connector with ignition on
- Check for intermittent faults by wiggling wiring while monitoring live data or fault memory
Signal parameters
- Solenoid coil resistance: typically low ohms (often in the range of ~1–20 Ω) — consult the vehicle service manual for exact spec
- Connector supply voltage: approximately battery voltage with ignition on (verify at pin)
- Ground continuity: near 0 Ω between connector ground and chassis ground
- Control signal: ABS module commonly modulates valve with a PWM signal (frequency and duty vary by system) — compare waveform to spec using scope
- No high-resistance connections; voltage drop under load should be minimal
Diagnostic algorithm
- Connect a diagnostic scan tool and read all ABS/ESP codes. Note freeze frame/live data related to the right rear valve.
- Clear codes and attempt to reproduce the fault by performing ABS pump/valve actuations via the scan tool or during a road test while monitoring live data.
- Visually inspect the valve electrical connector and harness for corrosion, damage, or water ingress. Repair or clean as needed.
- With ignition off, disconnect the valve connector and measure solenoid coil resistance. Compare to specification or the opposite-side valve if appropriate.
- With connector disconnected and ignition on, verify the presence of battery voltage on the supply pin and continuity to ground on the ground pin.
- If resistance and supply/ground are good but valve is not actuating, check for a control signal from the ABS module with a scope while commanding valve operation from the diagnostic tool.
- If control signal is present but valve does not respond, suspect mechanical failure of the valve or internal hydraulic unit fault — consider replacement of the hydraulic modulator or valve assembly.
- If there is no control signal but wiring and connector are good, suspect a fault in the ABS/ESP control module or its internal driver circuits.
- After repairs, clear codes and perform a road test and diagnostic verification to confirm the fault does not return.
Likely causes
- Solenoid coil resistance out of specification (open or short)
- Damaged connector pins/corrosion at the valve electrical connector
- Broken wire or intermittent harness fault between valve and ABS module
- Mechanical blockage or debris in the valve body preventing movement
- Faulty ABS modulator electronics driving the valve
- Low brake fluid level or contaminated fluid interfering with valve action
Fault status
Status
Right rear discharge valve malfunction — ABS hydraulic control circuit or valve failure detected.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
C1091
FIAT
C — Chassis
Right rear discharge valve
Views:
UK: 4
EN: 7
RU: 9
AI status
Completed
Completed
100%
Causes
- Open or shorted solenoid coil in the right rear discharge valve
- Corroded, loose, or damaged connector or wiring harness to the valve
- Poor ground or supply voltage to the ABS hydraulic unit
- Contamination or internal mechanical seizure of the valve
- Faulty ABS/ESP hydraulic control unit (modulator)
- Low brake fluid or air in hydraulic circuit affecting valve operation
Symptoms
- ABS warning light (and possibly traction control light) illuminated
- ABS or traction control functions reduced or disabled
- Changes in pedal feel during ABS activation or erratic ABS operation
- Brake performance affected under ABS activation (longer stopping distance)
- Possible diagnostic trouble codes for other ABS components or wheel sensors
What to check
- Read and record all stored ABS/ESP fault codes and freeze frame data with an appropriate scan tool
- Perform a visual inspection of the right rear discharge valve connector and wiring for damage, corrosion, or chafing
- Check brake fluid level and condition; inspect for contamination or leaks at the hydraulic unit
- Compare resistance of the right rear valve solenoid to the same valve on the opposite side (if identical) or to specification
- Verify battery voltage and ground at the valve connector with ignition on
- Check for intermittent faults by wiggling wiring while monitoring live data or fault memory
Signal parameters
- Solenoid coil resistance: typically low ohms (often in the range of ~1–20 Ω) — consult the vehicle service manual for exact spec
- Connector supply voltage: approximately battery voltage with ignition on (verify at pin)
- Ground continuity: near 0 Ω between connector ground and chassis ground
- Control signal: ABS module commonly modulates valve with a PWM signal (frequency and duty vary by system) — compare waveform to spec using scope
- No high-resistance connections; voltage drop under load should be minimal
Diagnostic algorithm
- Connect a diagnostic scan tool and read all ABS/ESP codes. Note freeze frame/live data related to the right rear valve.
- Clear codes and attempt to reproduce the fault by performing ABS pump/valve actuations via the scan tool or during a road test while monitoring live data.
- Visually inspect the valve electrical connector and harness for corrosion, damage, or water ingress. Repair or clean as needed.
- With ignition off, disconnect the valve connector and measure solenoid coil resistance. Compare to specification or the opposite-side valve if appropriate.
- With connector disconnected and ignition on, verify the presence of battery voltage on the supply pin and continuity to ground on the ground pin.
- If resistance and supply/ground are good but valve is not actuating, check for a control signal from the ABS module with a scope while commanding valve operation from the diagnostic tool.
- If control signal is present but valve does not respond, suspect mechanical failure of the valve or internal hydraulic unit fault — consider replacement of the hydraulic modulator or valve assembly.
- If there is no control signal but wiring and connector are good, suspect a fault in the ABS/ESP control module or its internal driver circuits.
- After repairs, clear codes and perform a road test and diagnostic verification to confirm the fault does not return.
Likely causes
- Solenoid coil resistance out of specification (open or short)
- Damaged connector pins/corrosion at the valve electrical connector
- Broken wire or intermittent harness fault between valve and ABS module
- Mechanical blockage or debris in the valve body preventing movement
- Faulty ABS modulator electronics driving the valve
- Low brake fluid level or contaminated fluid interfering with valve action
Fault status
Status
Right rear discharge valve malfunction — ABS hydraulic control circuit or valve failure detected.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
C1091
Other
C — Chassis
Speed Wheel Sensor All Coherency Failure
Views:
UK: 12
EN: 22
RU: 22
AI status
Completed
Completed
100%
Causes
- Open or shorted solenoid coil in the right rear discharge valve
- Corroded, loose, or damaged connector or wiring harness to the valve
- Poor ground or supply voltage to the ABS hydraulic unit
- Contamination or internal mechanical seizure of the valve
- Faulty ABS/ESP hydraulic control unit (modulator)
- Low brake fluid or air in hydraulic circuit affecting valve operation
Symptoms
- ABS warning light (and possibly traction control light) illuminated
- ABS or traction control functions reduced or disabled
- Changes in pedal feel during ABS activation or erratic ABS operation
- Brake performance affected under ABS activation (longer stopping distance)
- Possible diagnostic trouble codes for other ABS components or wheel sensors
What to check
- Read and record all stored ABS/ESP fault codes and freeze frame data with an appropriate scan tool
- Perform a visual inspection of the right rear discharge valve connector and wiring for damage, corrosion, or chafing
- Check brake fluid level and condition; inspect for contamination or leaks at the hydraulic unit
- Compare resistance of the right rear valve solenoid to the same valve on the opposite side (if identical) or to specification
- Verify battery voltage and ground at the valve connector with ignition on
- Check for intermittent faults by wiggling wiring while monitoring live data or fault memory
Signal parameters
- Solenoid coil resistance: typically low ohms (often in the range of ~1–20 Ω) — consult the vehicle service manual for exact spec
- Connector supply voltage: approximately battery voltage with ignition on (verify at pin)
- Ground continuity: near 0 Ω between connector ground and chassis ground
- Control signal: ABS module commonly modulates valve with a PWM signal (frequency and duty vary by system) — compare waveform to spec using scope
- No high-resistance connections; voltage drop under load should be minimal
Diagnostic algorithm
- Connect a diagnostic scan tool and read all ABS/ESP codes. Note freeze frame/live data related to the right rear valve.
- Clear codes and attempt to reproduce the fault by performing ABS pump/valve actuations via the scan tool or during a road test while monitoring live data.
- Visually inspect the valve electrical connector and harness for corrosion, damage, or water ingress. Repair or clean as needed.
- With ignition off, disconnect the valve connector and measure solenoid coil resistance. Compare to specification or the opposite-side valve if appropriate.
- With connector disconnected and ignition on, verify the presence of battery voltage on the supply pin and continuity to ground on the ground pin.
- If resistance and supply/ground are good but valve is not actuating, check for a control signal from the ABS module with a scope while commanding valve operation from the diagnostic tool.
- If control signal is present but valve does not respond, suspect mechanical failure of the valve or internal hydraulic unit fault — consider replacement of the hydraulic modulator or valve assembly.
- If there is no control signal but wiring and connector are good, suspect a fault in the ABS/ESP control module or its internal driver circuits.
- After repairs, clear codes and perform a road test and diagnostic verification to confirm the fault does not return.
Likely causes
- Solenoid coil resistance out of specification (open or short)
- Damaged connector pins/corrosion at the valve electrical connector
- Broken wire or intermittent harness fault between valve and ABS module
- Mechanical blockage or debris in the valve body preventing movement
- Faulty ABS modulator electronics driving the valve
- Low brake fluid level or contaminated fluid interfering with valve action
Fault status
Status
Right rear discharge valve malfunction — ABS hydraulic control circuit or valve failure detected.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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