Error code reference

Trane Furnace Error Code Solid ON

Internal control failure (ERR 18)

Internal control failure (ERR 18) - internal control failure within IFC.

First step from the service manual

Replace IFC.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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Step-by-step tests with expected resistance, voltage, and continuity values
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Internal control failure (ERR 18) - internal

From Service Manual 888518, p.50:

1.Replace IFC.

2.Measure control board supply voltage at the test points. Expected: 12 VDC and 5 VDC; a drop below 4.75 VDC on the logic rail points to a failed onboard regulator.

3.Inspect all connectors on the main control for corrosion, thermal stress, or backed-out pins. Reseat each connector with the power disconnected.

Part WPW10804018

Electronic control board

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First step from the service manual

Get the full diagnostic procedure for Solid ON.

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