1990 Chevrolet Pickup K2500, 2D Pickup, 5.0 H, Automatic, 400/M40FACTORY OEM SERVICE PROCEDURE

Code 25: Mat Sensor Temp. High (2.5L): Notes

The ECM applies and monitors a voltage signal (4-6 volts) to MAT sensor. When manifold air is cold, the sensor resistance is high and ECM sees a high signal voltage. As air warms, resistance decreases and voltage sensed by the ECM drops. Sensor resistance can be measured at sensor terminals with harness disconnected.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1)Β  This checks if the code is a hard failure or an intermittent condition. Code 25 will set if a VSS signal is present and MAT sensor temperature is greater than 302Β°F (150Β°C) is sensed for more than 2 seconds.

Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

When to See a Mechanic

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

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

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.