Code
C1090
ALFA ROMEO
C — Chassis
Right rear discharge valve
Views:
UK: 6
EN: 13
RU: 7
AI status
Completed
Completed
100%
Causes
- Open or short in the right rear discharge valve wiring (connector, harness damage, corroded pins)
- Poor or intermittent ground or supply voltage to the valve
- Stuck, clogged, or mechanically failed discharge valve (internal contamination)
- Faulty right rear discharge valve solenoid
- Faulty ABS/ESC control module or driver transistor
- Low brake fluid level or air in hydraulic system affecting valve operation
Symptoms
- ABS and/or traction control warning lamp illuminated
- Reduced or altered ABS operation; ABS may be disabled for that channel
- Longer braking distances or reduced stability system performance under heavy braking
- Unusual pump activity (runs more often) or audible clicking from ABS unit when activated
- Diagnostic trouble codes stored for ABS/ESC valve circuits
What to check
- Read all ABS/ESC codes and freeze frame data with a scanner; record live data while activating ABS valves where possible
- Visual inspection of right rear valve connector and wiring for corrosion, damage, or pin push-out
- Check battery and ignition supply to ABS module (12 V present with key ON)
- Check ground continuity from valve connector to chassis/engine ground
- Measure coil resistance of the valve solenoid (compare to manufacturer spec)
- Backprobe connector while commanding the valve with a scan tool and observe voltage/PWM and ground switching
Signal parameters
- Supply voltage to ABS hydraulics/valves: ~12 V nominal with ignition ON (verify on vehicle)
- Valve coil resistance typically in the low ohm range (example 10–40 Ω) — confirm with factory spec
- Control signal often ground-switched by ABS module; when activated expect PWM or switched ground (0 V) and varying duty cycle 0–100%
- When commanded OFF the control line may be floating or at supply voltage — compare live data to known-good values
- No CAN errors present when module communicating normally
Diagnostic algorithm
- Connect a calibrated scan tool and read/store all ABS/ESC fault codes and freeze frame. Clear codes and attempt to re-create the fault under the same conditions.
- Inspect the right rear discharge valve connector and harness for visual damage, corrosion or water ingress; repair as needed.
- With ignition ON (engine OFF) backprobe the valve connector: verify supply voltage, ground continuity and compare to reference. Command the valve from the scanner and observe control signal behavior.
- Measure valve coil resistance at the connector; if out of range compared with manufacturer specifications, replace the valve.
- If electrical supply and coil resistance are OK but the valve does not respond when commanded, test for PWM/driver output at the module side of the harness. If module driver is not switching, suspect ABS module fault.
- Inspect and correct brake fluid level and condition. If contamination suspected, flush hydraulic system and replace filter/valve as required.
- If intermittent, perform wiggle tests and road-test while monitoring live data. Replace wiring or valve if intermittent connector faults are found.
- After repairs clear codes and perform system bleed/self-test procedures per manufacturer. Confirm the code does not return.
Likely causes
- Corroded/loose connector or broken wire to the right rear valve
- Valve solenoid failed or contaminated/stuck by debris
- Module driver stage (internal transistor) failed
- Low fluid or hydraulic contamination preventing valve movement
Fault status
Status
Right rear discharge valve fault — electrical/hydraulic control error detected by ABS/ESC module.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Code
C1090
FIAT
C — Chassis
Right rear discharge valve
Views:
UK: 6
EN: 12
RU: 6
AI status
Completed
Completed
100%
Causes
- Open or short in the right rear discharge valve wiring (connector, harness damage, corroded pins)
- Poor or intermittent ground or supply voltage to the valve
- Stuck, clogged, or mechanically failed discharge valve (internal contamination)
- Faulty right rear discharge valve solenoid
- Faulty ABS/ESC control module or driver transistor
- Low brake fluid level or air in hydraulic system affecting valve operation
Symptoms
- ABS and/or traction control warning lamp illuminated
- Reduced or altered ABS operation; ABS may be disabled for that channel
- Longer braking distances or reduced stability system performance under heavy braking
- Unusual pump activity (runs more often) or audible clicking from ABS unit when activated
- Diagnostic trouble codes stored for ABS/ESC valve circuits
What to check
- Read all ABS/ESC codes and freeze frame data with a scanner; record live data while activating ABS valves where possible
- Visual inspection of right rear valve connector and wiring for corrosion, damage, or pin push-out
- Check battery and ignition supply to ABS module (12 V present with key ON)
- Check ground continuity from valve connector to chassis/engine ground
- Measure coil resistance of the valve solenoid (compare to manufacturer spec)
- Backprobe connector while commanding the valve with a scan tool and observe voltage/PWM and ground switching
Signal parameters
- Supply voltage to ABS hydraulics/valves: ~12 V nominal with ignition ON (verify on vehicle)
- Valve coil resistance typically in the low ohm range (example 10–40 Ω) — confirm with factory spec
- Control signal often ground-switched by ABS module; when activated expect PWM or switched ground (0 V) and varying duty cycle 0–100%
- When commanded OFF the control line may be floating or at supply voltage — compare live data to known-good values
- No CAN errors present when module communicating normally
Diagnostic algorithm
- Connect a calibrated scan tool and read/store all ABS/ESC fault codes and freeze frame. Clear codes and attempt to re-create the fault under the same conditions.
- Inspect the right rear discharge valve connector and harness for visual damage, corrosion or water ingress; repair as needed.
- With ignition ON (engine OFF) backprobe the valve connector: verify supply voltage, ground continuity and compare to reference. Command the valve from the scanner and observe control signal behavior.
- Measure valve coil resistance at the connector; if out of range compared with manufacturer specifications, replace the valve.
- If electrical supply and coil resistance are OK but the valve does not respond when commanded, test for PWM/driver output at the module side of the harness. If module driver is not switching, suspect ABS module fault.
- Inspect and correct brake fluid level and condition. If contamination suspected, flush hydraulic system and replace filter/valve as required.
- If intermittent, perform wiggle tests and road-test while monitoring live data. Replace wiring or valve if intermittent connector faults are found.
- After repairs clear codes and perform system bleed/self-test procedures per manufacturer. Confirm the code does not return.
Likely causes
- Corroded/loose connector or broken wire to the right rear valve
- Valve solenoid failed or contaminated/stuck by debris
- Module driver stage (internal transistor) failed
- Low fluid or hydraulic contamination preventing valve movement
Fault status
Status
Right rear discharge valve fault — electrical/hydraulic control error detected by ABS/ESC module.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
Similar codes
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Code
C1090
Generic
C — Chassis
ABS pump motor circuit malfunction
Views:
UK: 1
EN: 2
RU: 2
AI status
Completed
Completed
100%
Causes
- Open or short in the right rear discharge valve wiring (connector, harness damage, corroded pins)
- Poor or intermittent ground or supply voltage to the valve
- Stuck, clogged, or mechanically failed discharge valve (internal contamination)
- Faulty right rear discharge valve solenoid
- Faulty ABS/ESC control module or driver transistor
- Low brake fluid level or air in hydraulic system affecting valve operation
Symptoms
- ABS and/or traction control warning lamp illuminated
- Reduced or altered ABS operation; ABS may be disabled for that channel
- Longer braking distances or reduced stability system performance under heavy braking
- Unusual pump activity (runs more often) or audible clicking from ABS unit when activated
- Diagnostic trouble codes stored for ABS/ESC valve circuits
What to check
- Read all ABS/ESC codes and freeze frame data with a scanner; record live data while activating ABS valves where possible
- Visual inspection of right rear valve connector and wiring for corrosion, damage, or pin push-out
- Check battery and ignition supply to ABS module (12 V present with key ON)
- Check ground continuity from valve connector to chassis/engine ground
- Measure coil resistance of the valve solenoid (compare to manufacturer spec)
- Backprobe connector while commanding the valve with a scan tool and observe voltage/PWM and ground switching
Signal parameters
- Supply voltage to ABS hydraulics/valves: ~12 V nominal with ignition ON (verify on vehicle)
- Valve coil resistance typically in the low ohm range (example 10–40 Ω) — confirm with factory spec
- Control signal often ground-switched by ABS module; when activated expect PWM or switched ground (0 V) and varying duty cycle 0–100%
- When commanded OFF the control line may be floating or at supply voltage — compare live data to known-good values
- No CAN errors present when module communicating normally
Diagnostic algorithm
- Connect a calibrated scan tool and read/store all ABS/ESC fault codes and freeze frame. Clear codes and attempt to re-create the fault under the same conditions.
- Inspect the right rear discharge valve connector and harness for visual damage, corrosion or water ingress; repair as needed.
- With ignition ON (engine OFF) backprobe the valve connector: verify supply voltage, ground continuity and compare to reference. Command the valve from the scanner and observe control signal behavior.
- Measure valve coil resistance at the connector; if out of range compared with manufacturer specifications, replace the valve.
- If electrical supply and coil resistance are OK but the valve does not respond when commanded, test for PWM/driver output at the module side of the harness. If module driver is not switching, suspect ABS module fault.
- Inspect and correct brake fluid level and condition. If contamination suspected, flush hydraulic system and replace filter/valve as required.
- If intermittent, perform wiggle tests and road-test while monitoring live data. Replace wiring or valve if intermittent connector faults are found.
- After repairs clear codes and perform system bleed/self-test procedures per manufacturer. Confirm the code does not return.
Likely causes
- Corroded/loose connector or broken wire to the right rear valve
- Valve solenoid failed or contaminated/stuck by debris
- Module driver stage (internal transistor) failed
- Low fluid or hydraulic contamination preventing valve movement
Fault status
Status
Right rear discharge valve fault — electrical/hydraulic control error detected by ABS/ESC module.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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