C1256

Code

Other C — Chassis

ABS Inlet Valve Coil RR Circuit Short To Battery

Brand: Other

Type: C — Chassis

Views: UK: 28 EN: 43 RU: 29

AI status

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Page language: EN

Causes

Short in the RR inlet valve coil supply wire to constant battery feed
Damaged/shorted RR inlet valve coil
Corroded or damaged connector at the RR inlet valve or HCU (hydraulic control unit)
Aftermarket electrical accessory tied into the harness
Blown or incorrect fuse/relay affecting ABS power feed
Internal short in the ABS/HCU control module

Symptoms

ABS warning lamp illuminated and/or traction/stability lamp on
Possible ABS disabled or restricted functionality; longer/locked braking under ABS events
Stored DTC C1256 (may be accompanied by other ABS codes)
Possible drivability complaints during heavy braking or slippery conditions

What to check

Read ABS and vehicle fault codes and note freeze frame/store data
Perform visual inspection of RR wheel, harness and connector for damage, contamination or corrosion
Inspect and secure any aftermarket accessories or recent repairs near rear-right harness
Check fuses/relays for ABS power circuits (compare to schematic)
With ignition ON (engine off), probe the inlet valve connector for battery voltage and compare to expected states
Measure coil resistance with connector disconnected (see vehicle data)

Signal parameters

When uncommanded the coil feed should not have battery voltage present at the valve connector; when commanded the driver will supply voltage/ground per manufacturer design
Inlet valve coils are low-resistance devices (single-digit to low tens of ohms); consult factory service data for exact coil resistance and supply/drive voltages
Check for constant battery voltage on the coil feed terminal when system is off or not commanding the valve

Diagnostic algorithm

Retrieve and record all ABS codes and freeze frame. Note any related wheel speed or power-supply codes.
Visually inspect RR wheel speed sensor area and the ABS harness/connector for damage, corrosion, or moisture. Repair any obvious damage.
Disconnect the RR inlet valve connector at the HCU/valve body. With ignition ON (engine off), measure voltage at the suspected supply terminal. If battery voltage is present when it should not be, suspect a short to battery in the feed circuit or accessory splice.
With connector disconnected, measure coil resistance across valve coil pins and compare to manufacturer spec. An extremely low or near-zero reading may indicate an internal shorted coil.
Check continuity between the supply wire and battery positive with ignition OFF. Presence of continuity indicates a short to battery; trace wiring harness (inspect underbody, trunk, near chassis connections) to locate the short.
If wiring and connector are good but coil shows short, replace the RR inlet valve assembly. If coil and harness check OK, suspect the HCU driver—verify by back-probing and commanding valve operation with a scan tool and monitoring driver response.
After repair, clear codes, perform ABS actuator tests (if available) and road test to confirm repair. Re-scan to ensure C1256 does not return.
If diagnosis points to HCU internal failure, follow manufacturer procedures for module replacement or rebuild. Ensure immobilizer/vehicle programming procedures are followed if required.

Likely causes

Wiring chafe or pinched conductor contacting constant power source
Bent/water-corroded connector pin causing positive contact
Failed inlet valve coil with internal short
Incorrect repair/installation or aftermarket accessory splicing into harness
Faulty ABS/HCU driver circuit (less common)

Fault status

⚠️ Status

ABS warning lamp on. ABS module reports RR inlet valve coil circuit short to battery (DTC C1256). ABS may operate in a reduced or disabled mode until fault is repaired.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours