C1090

Code

ALFA ROMEO C — Chassis

Right rear discharge valve

Brand: ALFA ROMEO

Type: C — Chassis

Views: UK: 6 EN: 13 RU: 7

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Page language: EN

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

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

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

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

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.

⚠️ 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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