1990 Chevrolet Caprice Base, 4.3 Z, 4L60/MD8FACTORY OEM SERVICE PROCEDURE

Diagnostic Aids

If the engine is allowed to cool overnight, the coolant temperature sensor and MAT sensor should read close to each other, when measured with a "Scan" tester. A Code 25 will also result if sensor signal circuit is shorted to ground.

Fig 1: Code 25, MAT Sensor Temp Hi Ckt Diag
G110486
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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