C1108 — Air Trapped in Hydraulic System

C1108 — Air Trapped in Hydraulic System. Do not ignore C1108. If the hydraulic control feels spongy, leaks fluid, or shows changing response, have it inspected promptly. If the affected system is the brake hydraulic system, avoid driving until the concern is.

For Ford vehicles

air in hydraulic system

vehicle

Is it safe to drive?

Prompt hydraulic service recommended Do not ignore C1108. If the hydraulic control feels spongy, leaks fluid, or shows changing response, have it inspected promptly. If the affected system is the brake hydraulic system, avoid driving until the concern is corrected.

Typical symptoms

C1108 is stored as a confirmed or pending hydraulic-system fault.
Hydraulic fluid in the reservoir appears foamy or contains visible bubbles.
The affected hydraulic control feels slow, spongy, or less responsive.
The reservoir fluid level drops unexpectedly or a visible leak is present.
Operation may change after warming or during repeated hydraulic use.

Common causes

Air entered after a hydraulic line, fitting, hose, or component was opened.
A leaking fitting, hose, or seal allows air to enter the hydraulic circuit.
Low reservoir fluid level exposes the pump inlet and promotes aeration.
Foaming or contamination in the reservoir prevents air from separating from the fluid.
An incompletely bled cylinder, valve, or actuator leaves trapped air.
A worn pump or internal hydraulic valve draws air into the fluid.

How to diagnose with an OBD scanner

Confirm C1108 with a scanner Connect an ELM327 adapter or use AIScanAuto to read stored and pending codes. Confirm C1108 and review freeze-frame or live data for conditions present when the fault was recorded.
Inspect the hydraulic reservoir and lines With the system cool and depressurized, inspect the reservoir, hoses, fittings, lines, and surrounding surfaces for low fluid, leakage, contamination, foam, or visible bubbles.
Locate the source of air ingress Check the pump inlet, reservoir seals, hose connections, and recently serviced components. Repair damaged or leaking parts before attempting to bleed the system.
Bleed the hydraulic system correctly Add the specified hydraulic fluid and bleed each affected cylinder, valve, or actuator in the required sequence. Follow the vehicle-specific bleeding procedure because incorrect sequencing can leave air trapped.
Clear and verify the repair After correcting the cause and completing the bleed, use the scanner to clear C1108. Operate the hydraulic system under normal conditions and verify that the code does not return.

Approximate repair cost

A rough independent-shop estimate is USD 150-600 for hydraulic-system inspection, fluid service, and air bleeding; repairs involving a pump, valve, line, or cylinder can cost substantially more. These figures are estimates only, vary by region and vehicle, and are not verified repair quotes.

Common questions

Does C1108 always mean the hydraulic fluid is low?

No. C1108 identifies air in the hydraulic system, while low fluid can be one cause of that air. Leaks, foaming, pump problems, and incomplete bleeding must also be checked.

Can I continue driving with C1108 stored?

If the hydraulic control remains firm and no leak is present, driving cautiously to a repair facility may be reasonable. Do not drive if the response is soft, unstable, or accompanied by fluid loss.

Will clearing the C1108 code remove the air?

No. Clearing the code only erases the stored information. The air must be removed by correcting leaks or fluid conditions and properly bleeding the hydraulic system.

Can an ELM327 or AIScanAuto confirm the cause of C1108?

The scanner can confirm that C1108 is present and may provide related freeze-frame data, but it cannot identify the exact leak or air pocket. Physical inspection and a controlled bleed are still required.

C1108 — C1108 — Manufacturer Controlled DTC: Causes, Symptoms & Fix

When your check engine light comes on and a scan tool pulls code C1108, it means the vehicle's computer has detected that a sensor or actuator circuit is not behaving as expected during normal operation. C1108 falls into the manufacturer-controlled DTC category, which covers systems that vary between different makes and models. The ECU doesn't flag this code based on a single bad reading — it requires the fault to occur repeatedly under specific driving conditions before logging the code and illuminating the warning lamp. The freeze frame data stored alongside C1108 is particularly valuable for diagnosis—it captures the exact engine load, RPM, coolant temperature, and vehicle speed when the problem occurred, which helps pinpoint the specific conditions triggering the fault.

Modern vehicles rely on a complex network of sensors and actuators to monitor everything from engine performance to safety systems. When any link in this chain breaks down—whether through faulty wiring, a failed component, or a poor electrical connection—the affected module detects the abnormal behavior and sets C1108 to alert the driver. Because this code is manufacturer-controlled rather than standardized, the exact system affected differs from one vehicle to the next, making thorough investigation essential before pursuing any repairs.

Common Symptoms of C1108

Check Engine Light illuminated on the dashboard
Increased fuel consumption observed in some vehicles
Possible limp-home mode activation depending on which component is affected
The specific system tied to C1108 operates intermittently or stops working entirely

What Causes C1108?

An open circuit or shorted wiring within the affected electrical circuit
A blown fuse supplying power to the circuit
Corroded, loose, or physically damaged connector terminals
A faulty sensor or actuator within the circuit
A poor ground connection at the component or module
An internal driver fault within the control module itself

How to Diagnose C1108

Connect an OBD2 scanner and confirm C1108 is stored in the ECU memory. Save the freeze frame data—this snapshot of engine conditions when the fault occurred is your roadmap for recreating the problem during testing.
Look for related diagnostic trouble codes that may point to the underlying cause. Checking manufacturer technical service bulletins (TSB) for your specific make and model is worthwhile; many C0xxx code patterns have documented factory fixes or software updates available through the manufacturer website or NHTSA database.
Perform a detailed visual inspection of the wiring harness and connectors associated with the fault circuit. Look for damaged insulation, corrosion buildup, chafing from rubbing against bodywork, or pins that are pushed out of position.
Use a multimeter to check reference voltage, ground integrity, and signal continuity at the component connector while the system is powered up.
Conduct a wiggle test on the harness while monitoring live data on your scanner. Any signal dropouts or interruptions indicate a broken wire or intermittent connection that may not be visible during static inspection.
Clear the code from the ECU, then complete a full drive cycle that recreates the conditions recorded in the freeze frame. Verify that C1108 does not return before considering the repair complete.

How to Fix C1108

Target the most affordable and common culprits first before committing to expensive component replacement:

Replace the faulty sensor or actuator — $150–$500
Repair wiring or connectors — $80–$250
Control module repair or replacement — $300–$1,000

How Much Does It Cost to Fix C1108?

The total repair bill for C1108 depends entirely on which part of the circuit is actually at fault. Here are typical scenarios using independent shop labor rates in USD:

Replacing a failed sensor or actuator typically runs $150–$500 for parts and installation
Wiring harness repair or connector replacement generally costs $80–$250
Control module diagnosis and repair or replacement usually falls between $300–$1,000

Across all possible repair paths, fixing C1108 typically costs between $80 and $1,000. Getting an accurate diagnosis before purchasing parts is the smartest first step—the worst-case scenario is rarely where the problem actually lies.

Can You Drive with C1108?

In most situations the vehicle remains driveable, though you may notice reduced performance or a disabled auxiliary system. However, if the car exhibits stalling, a no-start condition, or warning lights related to brakes or steering, treat this as a priority repair and address it immediately.