Case IH Error Code 4120 — What It Means and How to Fix It

Applies to: Magnum Series, Steiger Series, Puma Series

CIH 4120Case IHManually verified

Hydraulic Oil Temperature — Over Limit

Hydraulic oil temperature has exceeded the safe operating limit. Continued operation risks seals, pump, and valve damage.

Repair difficulty

DIY — Basic tools

Repair time

30 min

Dealer cost

$250-600

Likely causes

  1. 1

    Clogged hydraulic oil cooler— Most likely

    The hydraulic cooler (usually mounted in front of the radiator) blocks up with chaff and dirt during harvest. Clean it with low-pressure air — never pressure wash from the front.

  2. 2

    Low hydraulic fluid level— Possible

    Less fluid means less thermal mass and less flow through the cooler. Check the level and look for leaks.

  3. 3

    Heavy continuous hydraulic demand— Possible

    Running large hydraulic cylinders or motors at full flow for extended periods generates heat. Allow the system to cool and check the cooler is clean.

  4. 4

    Failed hydraulic oil cooler thermostat— Less common

    Some models have a bypass thermostat in the hydraulic cooling circuit. If it sticks closed, oil bypasses the cooler entirely.

Parts needed

Tools needed

  • compressed air (low pressure)
  • fluid top-up container

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